Balanced high-frequency device and balance-characteristics improving method and balanced high-frequency circuit using the same

[0001] 1. Field of the Invention

[0002] The present invention relates to a balanced high-frequency device such as an surface acoustic wave filter or a high-frequency amplifier, a balanced high-frequency circuit using the balanced high-frequency device, a phase circuit, and a balance-characteristic improving method.

[0003] 2. Related Art of the Invention

[0004] Because mobile communication has recently advanced, improvement of performances of and downsizing of a device used are expected. Moreover, to improve noise characteristics to crosstalk between devices, balancing of a filter and a semiconductor device used for RF stage is progressed and a preferable balance-characteristic is requested. For a filter, an surface acoustic wave filter is more widely used. Particularly, in the case of a longitudinally coupled mode surface acoustic wave filter, balance-unbalance conversion can be easily realized because of the configuration of an IDT electrode and small loss, high attenuation, and preferable balance-characteristic are expected for an RF-stage filter having balanced input and output terminals.

[0005] A conventional balanced high-frequency device is described below. FIG. 28 shows a configuration of a conventional balanced high-frequency device 2801. The balanced high-frequency device 2801 is constituted by an input terminal IN serving as a unbalanced input/output terminal and output terminals OUT1 and OUT2 serving as balanced input/output terminals.

[0006] Moreover, in the case of a balanced high-frequency device, impedance matching is necessary. FIGS. 29(a) and 29(b) shows configurations of a conventional balanced high-frequency devices respectively having a matching circuit. In FIG. 29(a), a balanced high-frequency device 2901 is constituted by an input terminal IN serving as an unbalanced input/output terminal and output terminals OUT1 and OUT2 serving as balanced input/output terminals. Moreover, a matching circuit 2902 is connected between the output terminals OUT1 and OUT2. Moreover, in FIG. 29(b), a balanced high-frequency device 2903 is constituted by an input terminal IN serving as an unbalanced input/output terminal and output terminals OUT1 and OUT2 serving as balanced input/output terminals. Furthermore, matching circuits 2904 and 2905 are connected between the output terminals OUT1 and OUT2 and ground planes respectively. This type of the matching circuit is used to match a balanced high-frequency device with the characteristic impedance of a balanced input/output terminal.

[0007] As an example of the above balanced high-frequency device, a conventional surface acoustic wave filter is described below. FIG. 30 shows a block diagram of an surface acoustic wave filter 3001 having a balanced input/output terminal. In FIG. 30, the surface acoustic wave filter 3001 is constituted on a piezoelectric substrate 3002 by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode) 3003, 3004, and 3005 and first and second reflector electrodes 3006 and 3007. One-hand electrode finger of the first IDT electrode 3003 is connected to an output terminal OUT1 and the other-hand electrode finger of the first IDT electrode 3003 is connected to an output terminal OUT2. Moreover, one-hand electrode fingers of the second and third IDT electrodes 3004 and 3005 are connected to an input terminal IN and the other-hand electrode fingers of the electrodes 3004 and 3005 are grounded. By using the above configuration, it is possible to realize an surface acoustic wave filter having an unbalanced-balanced input/output terminal. Moreover, in the case of the surface acoustic wave filter in FIG. 30, impedances of the input and output terminals are respectively designed as 50 Ω.

[0008] Moreover, a conventional surface acoustic wave filter is described below as an example of a balanced high-frequency device having a matching circuit. FIG. 31 shows a block diagram of an surface acoustic wave filter 3101 having a matching circuit. In FIG. 31, the surface acoustic wave filter 3101 is constituted on a piezoelectric substrate 3102 by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode) 3103, 3104, and 3105 and first and second reflector electrodes 3106 and 3107. The first IDT electrode 3103 is divided into two divided IDT electrodes. One electrode finger of a first divided IDT electrode 3108 is connected to an output terminal OUT1, one electrode finger of a second divided IDT electrode 3109 is connected to an output terminal OUT2, and the other-hand electrode fingers of the first and second divided IDT electrodes are electrically connected. Moreover, one-hand electrode fingers of the second and third IDT electrodes 3104 and 3105 are connected to an input terminal IN and the other-hand electrode fingers of the electrodes 3104 and 3105 are grounded. Furthermore, an inductor 3110 is connected between output terminals as a matching circuit. By using the above configuration, it is possible to realize an surface acoustic wave filter having an unbalanced-balanced input/output terminal. Furthermore, in the case of the surface acoustic wave filter in FIG. 31, impedances of input and output terminals are designed as 50 Ω for the input side and as 150 Ω for the output side. Therefore, the filter has an impedance conversion function.

[0009] FIGS. 32(a) to 32(c) show characteristic diagrams of a conventional surface acoustic wave filter of a 900-MHz band shown in FIG. 30. In FIGS. 32(a) to 32(c), FIG. 32(a) shows a passing characteristic, FIG. 32(b) shows an amplitude balance-characteristic in a pass band (from 925 up to 960 MHz), and FIG. 32(c) shows a phase balance-characteristic in a pass band. From FIG. 32, it is found that the amplitude balance-characteristic greatly deteriorates from −0.67 dB to +0.77 dB and the phase balance-characteristic greatly deteriorates from −6.3° to +9.4° in each pass band.

[0010] In this case, the amplitude balance-characteristic denotes the difference between the signal amplitude of the input terminal IN and output terminal OUT1 and the signal amplitude of the input terminal IN and output terminal OUT2. When the difference becomes zero, the balance-characteristic does not deteriorate. Moreover, the phase balance-characteristic denotes a shift of the difference between the signal phase of the input terminal IN and output terminal OUT1 and the signal phase of the input terminal IN and output terminal OUT2 from 180°. When the difference becomes zero, the balance-characteristic does not deteriorate.

[0011] However, the above-described balanced high-frequency device and the surface acoustic wave filter described as an example of the device have a problem that the balance-characteristic which is one of important electrical characteristics is greatly deteriorated.

[0012] It is an object of the present invention to provide a balanced high-frequency device having a preferable balance-characteristic, a balanced high-frequency circuit, a phase circuit, and a balance-characteristic improving method by considering a deterioration cause about the balanced high-frequency device and thereby deriving a balance-characteristic improving method.

[0013] The 1st aspect of the present invention is a balanced high-frequency device comprising:

[0014] a balanced device having input terminals for inputting signals and output terminals for outputting signals; and

[0015] a phase circuit; wherein:

[0016] at least said input terminals or said output terminals are balanced input terminals or balanced output terminals;

[0017] said phase circuit is electrically connected between said balanced input terminals or said balanced output terminals; and

[0018] said phase circuit reduces common-mode signal components of said signals.

[0019] The 2nd aspect of the present invention is the balanced high-frequency device according to the 1st aspect, in which

[0020] said phase circuit is a resonant circuit which resonates at a predetermined frequency.

[0021] The 3rd aspect of the present invention is the balanced high-frequency device according to the 2nd aspect, in which

[0022] said resonant circuit is a series resonant circuit which series-resonates to a ground plane to common-mode signal components of said signals.

[0023] The 4th aspect of the present invention is the balanced high-frequency device according to the 2nd aspect, in which

[0024] said resonant circuit is a parallel resonant circuit which parallel-resonates to a ground plane to differential-mode signal components of said signals.

[0025] The 5th aspect of the present invention is the balanced high-frequency device according to any one of the 2nd to the 4th aspects, in which

[0026] said phase circuit includes a matching circuit to differential-mode signal components of said signals.

[0027] The 6th aspect of the present invention is the balanced high-frequency device according to any one of the 2nd to the 4th aspects, in which

[0028] said phase circuit includes a transmission line.

[0029] The 7th aspect of the present invention is the balanced high-frequency device according to the 6th aspect, in which

[0030] the length of said transmission line ranges between (λ/4+nλ) and (3λ/4nλ) when assuming λ as a wavelength and n as an integer.

[0031] The 8th aspect of the present invention is the balanced high-frequency device according to the 7th aspect, in which

[0032] the length of said transmission line ranges between (3λ/8+nλ) and (5λ/8nλ) when assuming λ as a wavelength and n as an integer.

[0033] The 9th aspect of the present invention is the balanced high-frequency device according to the 8th aspect, in which

[0034] the length of said transmission line is substantially equal to λ/2.

[0035] The 10th aspect of the present invention is the balanced high-frequency device according to the 9th aspect, in which

[0036] said phase circuit operates substantially as a series resonant circuit of a opened λ/4 line for common-mode signal components of said signals and as a parallel resonant circuit of a shorted λ/4 line for differential-mode signal components of said signals.

[0037] The 11th aspect of the present invention is the balanced high-frequency device according to any one of the 2nd to the 4th aspects, in which

[0038] said phase circuit includes at least three impedance elements, and

[0039] impedances of common-mode signal components of said signals to a ground plane is set lower than the impedance of differential-mode signal components of said signals to a ground plane for impedances of said balanced input terminals or balanced output terminals with a ground plane.

[0040] The 12th aspect of the present invention is the balanced high-frequency device according to the 11th aspect, in which

[0041] a first impedance element is connected between one of said balanced input terminals or one of said balanced output terminals and a ground plane,

[0042] a second impedance element is connected between the other of said balanced input terminals or the other of said balanced output terminals and a ground plane,

[0043] a third impedance element is connected between said balanced input terminals or said balanced output terminals, and

[0044] imaginary parts of impedances of said first and second impedance elements are different from the imaginary part of the impedance of said third impedance element in polarity.

[0045] The 13th aspect of the present invention is the balanced high-frequency device according to the 12th aspect, in which

[0046] said first impedance element and said third impedance element on one hand and said second Impedance element and said third impedance element on the other respectively form a parallel resonant circuit to a ground plane at a predetermined frequency for differential-mode signal components of said signals.

[0047] The 14th aspect of the present invention is the balanced high-frequency device according to the 12th aspect, in which

[0048] the impedance between one of said balanced input terminals or one of said balanced output terminals and a ground plane and the impedance between the other of said balanced input terminals or the other of said balanced output terminals and a ground plane are respectively substantially equal to or less than 2×Z0 when assuming a characteristic impedance as Z0.

[0049] The 15th aspect of the present invention is the balanced high-frequency device according to the 14th aspect, in which

[0050] impedances of the common-mode signal components of said signal to a ground plane is substantially equal to or less than 0.5×Z0 when assuming a characteristic impedance as Z0.

[0051] The 16th aspect of the present invention is the balanced high-frequency device according to the 11th aspect, in which

[0052] a first impedance element and a second impedance element are connected between balanced input terminals or balanced output terminals in series,

[0053] the portion between said first impedance element and said second impedance element are grounded through a third impedance element, and

[0054] imaginary parts of impedances of said first and second impedance elements are different from the imaginary part of the impedance of said third impedance element in polarity.

[0055] The 17th aspect of the present invention is the balanced high-frequency device according to the 16th aspect, characterized in that

[0056] said first impedance element and said third impedance element on one hand and said second impedance element and said third impedance element on the other respectively form a series resonant circuit to a ground plane at a predetermined frequency about common-mode signal components of said signals.

[0057] The 18th aspect of the present invention is the balanced high-frequency device according to any one of the 1st to the 4th aspects, in which

[0058] said balanced device is an surface acoustic wave filter,

[0059] said surface acoustic wave filter has a piezoelectric substrate and a plurality of IDT electrodes (inter-digital transducer electrodes) formed on said piezoelectric substrate, and

[0060] at least one of said IDT electrodes is connected to a balanced input terminal or balanced output terminal.

[0061] The 19th aspect of the present invention is the balanced high-frequency device according to the 18th aspect, in which

[0062] said surface acoustic wave filter is a longitudinally coupled-mode surface acoustic wave filter obtained by arranging at least first, second, and third IDT electrodes along the propagative direction of an elastic surface-wave,

[0063] said second and third IDT electrodes are arranged at the both sides of said first IDT electrode,

[0064] said first IDT electrode is the balanced type and one and the other electrode fingers constituting said first IDT electrode are respectively connected to a balanced input terminal or balanced output terminal.

[0065] The 20th aspect of the present invention is the balanced high-frequency device according to the 18th aspect, in which

[0066] said surface acoustic wave filter is a longitudinally coupled-mode surface acoustic wave filter obtained by arranging at least first, second, and third IDT electrodes along the propagative direction of an elastic surface-wave,

[0067] said second and third IDT electrodes are arranged at the both sides of said first IDT electrode,

[0068] said first IDT electrode is constituted by a plurality of divided IDT electrodes, and

[0069] at least two of said divided IDT electrodes are respectively connected to a balanced input terminal or a balanced output terminal.

[0070] The 21st aspect of the present invention is the balanced high-frequency device according to the 18th aspect, in which

[0071] said surface acoustic wave filter is a longitudinally coupled mode surface acoustic wave filter obtained by arranging at least first, second, and third IDT electrodes along the propagative direction of an elastic surface-wave,

[0072] said second and third IDT electrodes are arranged at the both sides of said first IDT electrode,

[0073] said second IDT electrode is connected to one of balanced input terminals or one of balanced output terminals,

[0074] said third IDT electrode is connected to the other of said balanced input terminals or the other of said balanced output terminals.

[0075] The 22nd aspect of the present invention is the balanced high-frequency device according to any one of the 1st to 4th aspects, in which

[0076] said balanced device is a semiconductor device.

[0077] The 23rd aspect of the present invention is the balanced high-frequency device according to the 22nd aspect, in which

[0078] said semiconductor device is an amplifier constituted by a plurality of transistors.

[0079] The 24th aspect of the present invention is the balanced high-frequency device according to any one of the 1st to the 4th aspects, in which

• • [0080] at least a part of said phase circuit is constituted so as to be included in a laminated device formed by forming electrode patterns on a plurality of dielectric layers and laminating said dielectric layers.

[0081] The 25th aspect of the present invention is the balanced high-frequency device according to the 24th aspect, in which

• • [0082] said laminated device has at least one circuit function and said balanced high-frequency device and laminated device are compounded.

[0083] The 26th aspect of the present invention is a balanced high-frequency circuit comprising the balanced high-frequency device according to any one of the 1st to the 4th aspects.

[0084] The 27th aspect of the present invention is the balanced high-frequency circuit according to the 26th aspect, in which

[0085] a transmitting filter and/or a receiving filter which constitute or constitutes said balanced high-frequency circuit use or uses the balanced high-frequency device according to the 18^th aspect.

[0086] The 28th aspect of the present invention is the balanced high-frequency circuit according to the 26th aspect, in which

[0087] a transmitting amplifier and/or a receiving amplifier which constitute or constitutes said balanced high-frequency circuit use or uses the balanced high-frequency device according to the 22nd aspect.

[0088] The 29th aspect of the present invention is a balanced high-frequency circuit comprising:

[0089] a circuit substrate; and

[0090] balanced transmission lines set to said circuit substrate, in which

[0091] the phase circuit according to any one of the 1st to 4th aspects is connected between said balanced transmission lines.

[0092] The 30th aspect of the present invention is a phase circuit comprising:

[0093] a phase-circuit section having an output terminal electrically connected between balanced input terminals or balanced output terminals of a balanced device which has input terminals for inputting signals and output terminals for outputting signals and in which at least said input terminals or said output terminals are said balanced input terminals or said balanced output terminals to reduce common-mode signal components of said signals.

[0094] The 31st aspect of the present invention is a balance-characteristics improving method comprising:

[0095] an in-phase-signal-component reducing step of reducing in-phase signal components of signals between balanced input terminals or balanced output terminals of a balanced device which has input terminals for inputting signals and output terminals for outputting signals and in which at least said input terminals or said output terminals are balanced input terminals or balanced output terminals.

• [0128] 101 Balanced high-frequency device
• [0129] 102 Balanced device
• [0130] 103 Phase circuit
• [0131] 201 Surface acoustic wave filter
• [0132] 202 Ideal surface acoustic wave filter
• [0133] 203, 204 Capacity component
• [0134] 501 Balanced high-frequency device
• [0135] 502 Balanced device
• [0136] 503, 504 Phase circuit
• [0137] 601 Balanced high-frequency device
• [0138] 602 Balanced device
• [0139] 603 Phase circuit
• [0140] 604 Transmission line
• [0141] 801 Balanced high-frequency device
• [0142] 802 Balanced device
• [0143] 803 Phase circuit
• [0144] 805, 806 Impedance element
• [0145] 901 Phase circuit
• [0146] 902, 903 Capacitor
• [0147] 904 Inductor
• [0148] 905 Virtual ground point
• [0149] 1001 Phase circuit
• [0150] 1002, 1003 inductor
• [0151] 1004 Capacitor
• [0152] 1005 Virtual ground point
• [0153] 1101 Balanced high-frequency device
• [0154] 1102 Balanced device
• [0155] 1103 Phase circuit
• [0156] 1104, 1105, 1106 Impedance element
• [0157] 1201 Phase circuit
• [0158] 1202, 1203 Inductor
• [0159] 1204 Capacitor
• [0160] 1205 Connection point
• [0161] 1301 Phase circuit
• [0162] 1302, 1303 Capacitor
• [0163] 1304 Inductor
• [0164] 1305 Connection point
• [0165] 1401 Balanced high-frequency device
• [0166] 1402 Surface acoustic wave filter
• [0167] 1403 Phase circuit
• [0168] 1404 Piezoelectric substrate
• [0169] 1405 First IDT electrode
• [0170] 1406 Second IDT electrode
• [0171] 1407 Third IDT electrode
• [0172] 1408 First reflector electrode
• [0173] 1409 Second reflector electrode
• [0174] 1601, 1801, 2001 Maximum value of amplitude balance-characteristic deterioration of conventional surface acoustic wave filter
• [0175] 1602, 1802, 2002 Minimum value of amplitude balance-characteristic deterioration of conventional surface acoustic wave filter
• [0176] 1603, 1803, 2003 Maximum value of phase balance-characteristic deterioration of conventional surface acoustic wave filter
• [0177] 1604, 1804, 2004 Minimum value of phase balance-characteristic deterioration of conventional surface acoustic wave filter
• [0178] 2101, 2102 Region showing vicinity of band pass frequency
• [0179] 2201 Phase circuit
• [0180] 2202 Capacitor
• [0181] 2301 Balanced high-frequency device
• [0182] 2302 Phase circuit
• [0183] 2304, 2305 Capacitor
• [0184] 2306 Inductor
• [0185] 2307 Inductor serving as matching circuit
• [0186] 2308 Virtual ground point
• [0187] 2309 Combined inductor
• [0188] 2401 Balanced high-frequency device
• [0189] 2402 Surface acoustic wave filter
• [0190] 2403 Phase circuit
• [0191] 2404 Piezoelectric substrate
• [0192] 2405 First IDT electrode
• [0193] 2406 Second IDT electrode
• [0194] 2407 Third IDT electrode
• [0195] 2408 First reflector electrode
• [0196] 2409 Second reflector electrode
• [0197] 2410 First divided IDT electrode
• [0198] 2411 Second divided IDT electrode
• [0199] 2501 Balanced high-frequency device
• [0200] 2502 Surface acoustic wave filter
• [0201] 2503 Phase circuit
• [0202] 2504 Piezoelectric substrate
• [0203] 2505 First IDT electrode
• [0204] 2506 Second IDT electrode
• [0205] 2507 Third IDT electrode
• [0206] 2508 First reflector electrode
• [0207] 2509 Second reflector electrode
• [0208] 2601 Balanced high-frequency device
• [0209] 2602 Semiconductor device
• [0210] 2603 Phase circuit
• [0211] 2604a, 2604b, 2605a, 2605b Bipolar transistor
• [0212] 2606a, 2606b Inductor
• [0213] 2607 DC-cut capacitor
• [0214] 2608 Bypass capacitor
• [0215] 2609a, 2609b DC-cut capacitor
• [0216] 2610, 2611 Bias circuit
• [0217] 2612a, 2612b Choke inductor
• [0218] 2701 Balanced high-frequency circuit on substrate
• [0219] 2702 Transmitting amplifier
• [0220] 2703 Transmitting filter
• [0221] 2704 Switch
• [0222] 2705 Antenna
• [0223] 2706 Receiving filter
• [0224] 2707 Receiving amplifier
• [0225] 2708, 2709 Balanced transmission line
• [0226] 2801, 2901 Balanced high-frequency device
• [0227] 2902, 2904, 2905 Matching circuit
• [0228] 2903 Balanced high-frequency device
• [0229] 3001 Surface acoustic wave filter
• [0230] 3002 Piezoelectric substrate
• [0231] 3003 First IDT electrode
• [0232] 3004 Second IDT electrode
• [0233] 3005 Third IDT electrode
• [0234] 3006 First reflector electrode
• [0235] 3007 Second reflector electrode
• [0236] 3101 Surface acoustic wave filter
• [0237] 3102 Piezoelectric substrate
• [0238] 3103 First IDT electrode
• [0239] 3104 Second IDT electrode
• [0240] 3105 Third IDT electrode
• [0241] 3106 First reflector electrode
• [0242] 3107 Second reflector electrode
• [0243] 3108 First divided IDT electrode
• [0244] 3109 Second divided IDT electrode
• [0245] 3110 Inductor

[0246] Embodiments of the present invention are described below by referring to the accompanying drawings.

[0247] A balanced high-frequency device of embodiment 1 of the present invention is described below by referring to the accompanying drawings. FIG. 1 shows a configuration of a balanced high-frequency device 101 of the embodiment 1 of the present invention. In FIG. 1, the balanced high-frequency device 101 is constituted by a balanced device 102 and a phase circuit 103. Moreover, in the case of a balanced device 102, the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and the output-side terminals are output terminals OUT1 and OUT2 serving as balanced input/output terminals. Furthermore, a phase circuit 103 is connected between the output terminals. By using the above configuration, it is possible to realize a balanced high-frequency device having an unbalanced-balanced input/output terminal.

[0248] First, a balance-characteristic deterioration cause of the balanced high-frequency device is studied by using an surface acoustic wave filter. The conventional surface acoustic wave filter 201 shown in FIG. 30 has a problem that a balance-characteristic deteriorates. In this case, the balance-characteristic is analyzed by the configuration shown in FIG. 2. In FIG. 2, the surface acoustic wave filter 201 is constituted by an ideal surface acoustic wave filter 202 whose balance-characteristic is not deteriorated and capacitive components 203 and 204. Combination by the parasitic component of the surface acoustic wave filter 201 is assumed by connecting the capacitive components 203 and 204 between the input side and output side of the ideal surface acoustic wave filter 202.

[0249] FIGS. 3(a) and 3(b) show filter characteristics when setting these capacitive components 203 and 204 to substantially 0.1 pF in which FIG. 3(a) shows an amplitude balance-characteristic in a pass band and FIG. 3(b) shows a phase balance-characteristic in a pass band. A result of analyzing the balance-characteristic in FIG. 3 very well coincides with the measured characteristic of the conventional surface acoustic wave filter shown in FIG. 32 as a trend of balance-characteristic deterioration. Therefore, combination of the input terminal and output terminal of a balanced device is considered as a main factor of balance-characteristic deterioration.

[0250] Operations of the balanced high-frequency device of the embodiment 1 of the present invention are described below by referring to the accompanying drawings. FIG. 4 shows the outline of operations of the balanced high-frequency device 101 of the embodiment 1 of the present invention. Combination due to a parasitic component between an input terminal and an output terminal is estimated as a main factor of deterioration of the balance-characteristic of the balanced high-frequency device 101. It is considered that the above mentioned can be explained by showing a signal component flowing through balanced input and output terminals by an common-mode signal component and a differential-mode signal component. Here, common-mode signal component means in-phase signal component, and differential-mode signal component means opposite-phase signal component. That is, a signal component i input from the input terminal IN is differentially output as differential-mode signal components id1 and id2 by the balanced device 102. However, the combination by a parasitic component is not made differential by the output terminal OUT1 or OUT2 but it is superimposed as common-mode signal components ic1 and ic2 and the common-mode signal components ic1 and ic2 cause the balance-characteristic to deteriorate.

[0251] Therefore, in the case of an embodiment of the present invention, it is possible to reduce the common-mode components ic1 and ic2 when the phase circuit 103 operates as a resonant circuit at a predetermined frequency to make impedances of the common-mode signal components ic1 and ic2 when viewing the output-terminal side from the balanced device 102 lower than impedances of the differential-mode signal components id1 and id2 when viewing the output-terminal side from the balanced device 102.

[0252] As described above, the balanced high-frequency device 101 of the present invention realizes a balanced high-frequency device excellent in balance-characteristic by reducing the common-mode signal components ic1 and ic2 by the phase circuit 103.

[0253] In the case of this embodiment, it is described that the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal, the output-side terminals are output terminals OUT1 and OUT2 serving as balanced input/output terminals, and the phase circuit 103 is connected between the output terminals. However, this embodiment is not restricted to the above case. It is also allowed that the input-side terminal is an input terminal serving as a balanced input/output terminal, the output-side terminal is an output terminal serving as an unbalanced input/output terminal, and the phase circuit 103 is connected between input terminals.

[0254] A balanced high-frequency device of embodiment 2 of the present invention is described below by referring to the accompanying drawings. FIG. 5 shows a configuration of a balanced high-frequency device 501 of the embodiment 2 of the present invention. In FIG. 5, the balanced high-frequency device 501 is constituted by a balanced device 502 and phase circuits 503 and 504. Moreover, in the case of the balanced device 502, the input-side terminal is an input terminal IN serving as a balanced input/output terminal and the output-side terminals are output terminals OUT1 and OUT2 serving as balanced input/output terminals. By using the above configuration, it is possible to realize a balanced high-frequency device having balanced-balanced input and output terminals.

[0255] Also in the case of the balanced high-frequency device 501 of the present invention, it is possible to realize a balanced high-frequency device excellent in balance-characteristic because the phase circuit 503 operates as a resonant circuit at a predetermined frequency and makes impedances of common-mode signal components ic1 and ic2 when viewing the input-terminal side from the balanced device 502 lower than those of differential-mode signal components id1 and id2 when viewing the input-terminal side from the balanced device 502 and the phase circuit 504 operates as a resonant circuit at a predetermined frequency and makes impedances of the common-mode signal components ic1 and ic2 when viewing the output-terminal side from the balanced device 502 lower than those of the differential-mode signal components id1 and id2 when viewing the output-terminal side from the balanced device 502 and thereby, reduces the common-mode signal components ic1 and ic2.

[0256] A balanced high-frequency device of embodiment 3 of the present invention is described below by referring to the accompanying drawings. A more specific circuit configuration is shown below as a phase circuit. FIG. 6 shows a configuration of a balanced high-frequency device 601 of the embodiment 2 of the present invention. In FIG. 6, the balanced high-frequency device 601 is constituted by a balanced device 602 and a phase circuit 603. Moreover, in the case of the balanced device 602, the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT1 and OUT2 serving as balanced input/output terminals. Furthermore, the phase circuit 603 is constituted by a transmission line 604 and set between output terminals. The transmission line 604 has a length of λ/2 (in this case, λ denotes a wavelength) which corresponds to a phase shift of 180°. Furthermore, in this case, λ is equal to a frequency in a pass band or nearby the pass band. By using the above configuration, it is possible to realize a balanced high-frequency device having an unbalanced-balanced input/output terminal.

[0257] Operations of the balanced high-frequency device 601 are described by referring to the accompanying drawings. As shown in FIG. 7(a), when a signal component i is input to the balanced device 602 from the input terminal IN, common-mode signal components ic1 and ic2 and differential-mode signal components id1 and id2 are output from the balanced device. A transmission line 604 set between output terminals performs operations different from each other for the common-mode signal components ic1 and ic2 and differential-mode signal components id1 and id2. That is, as shown in FIG. 7(b), for the common-mode signal components ic1 and ic2, a configuration is realized in which a opened λ/4 line is connected to the output terminals OUT1 and OUT2 respectively and operates as a series resonant circuit, impedances of the output terminals to a ground plane almost becomes short, and the common-mode signal component id1 or ic2 is not propagated to the output terminal OUT1 or OUT2.

[0258] Moreover, for the differential-mode signal components id1 and id2, a configuration is realized in which shorted λ/4 line is connected to the output terminals OUT1 and OUT2 respectively because a virtual setting plane is formed at the middle point of the transmission line 604, operates as a parallel resonant circuit, and impedances of the output terminals to ground planes almost become open, and thereby the differential-mode signal components id1 and id2 are propagated to the output terminals OUT1 and OUT2.

[0259] As described above, the balanced high-frequency device of the embodiment 3 of the present invention makes it possible to reduce common-mode signal components by using the transmission line 604 as a phase circuit and thus, it is possible to realize a balanced high-frequency device excellent in balance-characteristic.

[0260] In the case of this embodiment, the phase circuit is constituted by the transmission line. However, the configuration of the phase circuit is not restricted to the above configuration. By using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained.

[0261] Moreover, it is allowed that a phase circuit is formed on a circuit substrate by using a transmission line and a chip component or integrated on a substrate with a balanced device mounted or in a package. Furthermore, it is allowed to form a part of the phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating the laminated device with a balanced high-frequency device of the present invention as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device.

[0262] In the case of this embodiment, an input terminal is described as the unbalanced type and an output terminal is described as the balanced type. However, it is allowed that an input terminal is the balanced type and an output terminal is the unbalanced type. Moreover, it is allowed that both input terminal and output terminal are the balanced type.

[0263] A balanced high-frequency device of embodiment 4 of the present invention is described below by referring to the accompanying drawings. A more specific circuit configuration is shown below as a phase circuit. FIG. 8 shows a configuration of a balanced high-frequency device of the embodiment 4 of the present invention. In FIG. 8, the balanced high-frequency device 801 is constituted by a balanced device 802 and a phase circuit 803. In the case of the balanced device 802, the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT1 and OUT2 serving as balanced input/output terminals.

[0264] The phase circuit 803 is constituted by impedance elements 804, 805, and 806. In this case, the output terminals OUT1 and OUT2 are grounded through impedance elements 804 and 805, the impedance element 806 is connected between the output terminals, and the phase circuit 803 is also connected between the output terminals. In this case, the impedance elements 804 and 805 substantially have the same impedance and the imaginary part of the impedance of the impedance element 806 is reverse to that of the impedances of the impedance elements 804 and 805 in polarity. By using the above configuration, a balanced high-frequency device having unbalanced-balanced input and output terminals can be obtained.

[0265] Then, operations of the balanced high-frequency device of the embodiment 4 of the present invention are described below by using a specific impedance element. FIGS. 9(a) and 9(b) are illustrations for explaining operations of the balanced high-frequency device of the embodiment 4 of the present invention. As shown in FIG. 9(a), a phase circuit 901 is constituted by capacitors 902 and 903 and an inductor 904. As shown in FIG. 9(a), when a signal component i is input to the balanced device 802 from the input terminal IN, common-mode signal components ic1 and ic2 and differential mode signal components id1 and id2 are output from the balanced device. In this case, the inductor 904 connected between output terminals forms a virtual ground point 905 on the differential-mode signal components id1 and id2.

[0266] FIG. 9(b) shows the equivalent circuit of the phase circuit 901 on the differential-mode signal components id1 and id2. Because the inductor 904 forms the virtual ground point 905 on the differential-mode signal components id1 and id2, the capacitor 902 and a part of the inductor 904 form a parallel resonant circuit to a ground plane at the output terminal OUT1 and the capacitor 903 and a part of the inductor 904 form a parallel resonant circuit to a ground plane at the output terminal OUT2. By designing parallel resonant frequencies of the parallel resonant circuits so as to be kept in a pass band or nearby the pass band, impedances of the differential-mode signal components id1 and id2 at a predetermined frequency to a ground plane approach infinity and transferred to the output terminals without being shorted to a ground plane. That is, on the differential-mode signal components, operations substantially same as those shown in FIG. 7(c) are executed. FIG. 9(c) shows the equivalent circuit of the phase circuit 901 on the common-mode signal components ic1 and ic2. OUT1 and OUT2 have almost equal potentials on the common-mode signal components, the inductor 904 does not form a virtual ground point on the common-mode signal components ic1 and ic2, and OUT1 and OUT2 are substantially open. In this case, a part of the inductor 904 denotes a range up to the virtual ground point 905 {refer to FIG. 9(b)}.

[0267] Thus, by designing impedances of the capacitors 902 and 903 serving as impedance elements arranged between the balanced input/output terminals OUT1 and OUT2 and ground planes to sufficiently small values, the common-mode signal components ic1 and ic2 are shorted to ground planes and therefore, they are not transferred to the balanced input/output terminals.

[0268] Moreover, it is allowed that the phase circuit of the embodiment 4 of the present invention has the configuration shown in FIG. 10. FIGS. 10(a) to 10(c) are illustrations for explaining operations of the balanced high-frequency device of the embodiment 4 of the present invention. As shown in FIG. 10(a), a phase circuit 1001 is constituted by inductors 1002 and 1003 and a capacitor 1004. As shown in FIG. 10(a), when a signal component i is input to a balanced device 802 from an input terminal IN, common-mode signal components ic1 and ic2 and differential-mode signal components id1 and id2 are output from the balanced device. In this case, the capacitor 1004 connected between output terminals forms a virtual ground point 1005 on differential-mode signal components id1 and id2.

[0269] FIG. 10(b) shows the equivalent circuit of the phase circuit 1001 on the differential-mode signal components id1 and id2. As shown in FIG. 10(b), because the capacitor 1004 forms a virtual ground point 1005 on the differential-mode signal components id1 and id2, the inductor 1002 and a part of the capacitor 1004 form a parallel resonant circuit to a ground plane at the output terminal OUT1 and the inductor 1003 and a part of the capacitor 1004 form a parallel resonant circuit to a ground plane at the output terminal OUT2. Therefore, by designing parallel resonant frequencies of the parallel resonant circuits so that they are kept in a pass band or nearby the pass band, impedances of the differential-mode signal components id1 and id2 at desired frequencies to a ground plane approach infinity and the components are transferred to the output terminals without being shorted to ground planes. That is, operations substantially same as those shown in FIG. 7(c) are executed on the differential-mode signal components id1 and id2. FIG. 10(c) shows the equivalent circuit of the phase circuit 1001 on the common-mode signal components ic1 and ic2. OUT1 and OUT2 have almost equal potential on the common-mode signal components, the capacitor 1004 does not form a virtual ground point on the common-mode signal component ic1 or ic2, and OUT1 and OUT2 substantially become open. In this case, a part of the capacitor 1004 denotes a range up to the virtual ground point (refer to FIG. 10(b)).

[0270] Therefore, by designing impedances of the inductors 1002 and 1003 serving as impedance elements arranged between the balanced input/output terminals OUT1 and OUT2 and ground planes to sufficiently small values, the common-mode signal components id1 and ic2 are shorted to ground planes and therefore, they are not transferred to the balanced input terminals.

[0271] As described above, in the case of the balanced high-frequency device of the embodiment 4 of the present invention, it is possible to reduce common-mode signal components by using three impedance elements as phase circuits and thus, realize a balanced high-frequency device excellent in balance-characteristic.

[0272] In the case of this embodiment, the numbers of and configurations of inductors and capacitors serving as impedance elements constituting a phase circuit are not restricted to the above case. Moreover, though device values of the impedance elements 804 and 805 are substantially equal to each other, it is not always necessary that they are equal to each other. They are optimally selected in accordance with a circuit configuration. By using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained.

[0273] Moreover, it is allowed that a phase circuit is formed on a circuit substrate by using a transmission line and a chip component or integrated on a substrate with a balanced device mounted or in a package. Furthermore, it is allowed to form a part of the phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating the laminated device with a balanced high-frequency device of the present invention as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device.

[0274] Furthermore, in the case of this embodiment, it is described that an input terminal is the unbalanced type and an output terminal is the balanced type. However, it is allowed that the input terminal is the balanced type and the output terminal is the unbalanced type. Furthermore, it is allowed that both the input terminal and output terminal are the balanced type.

[0275] A balanced high-frequency device of embodiment 5 of the present invention is described below by referring to the accompanying drawings. A more specific circuit configuration is shown below as a phase circuit. FIG. 11 shows a configuration of a balanced high-frequency device 1101 of the embodiment 5 of the present invention. In FIG. 11, the balanced high-frequency device 1101 is constituted by a balanced device 1102 and a phase circuit 1103. Moreover, in the case of the balanced device 1102, the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT1 and OUT2 serving as balanced terminals.

[0276] The phase circuit 1103 is constituted by impedance elements 1104, 1105, and 1106. The impedance elements 1104 and 1105 are connected between the output terminals in series and the middle point 1107 between the impedance elements 1104 and 1105 is grounded through the impedance element 1106 and the phase circuit 1103 is connected between the output terminals. In this case, the imaginary part of the impedance of the impedance element 1106 is opposite to imaginary parts of impedances of the impedance elements 1104 and 1105 in polarity. Moreover, the impedance elements 1104 and 1105 have the substantially same value. By using the above configuration, it is possible to obtain a balanced high-frequency device having an unbalanced-balanced input/output terminal.

[0277] Then, operations of a balanced high-frequency device of the present invention are described below by using a specific impedance element. FIGS. 12(a) to 12(c) are illustrations for explaining operations of the balanced high-frequency device of the present invention. As shown in FIG. 12(a), a phase circuit 1201 is constituted by inductors 1202 and 1203 and a capacitor 1204. As shown in FIG. 12(a), when a signal component i is input from an input terminal IN to the balanced device 1102, common-mode signal components ic1 and ic2 and differential-mode signal components id1 and id2 are output from the balanced device 1102. FIG. 12(b) shows the equivalent circuit of the phase circuit 1201 on the differential-mode signal components. As shown in FIG. 12(b), the connection point 1205 between the inductors 1202 and 1203 serves as a virtual ground point on the differential-mode signal components id1 and id2. Therefore, by sufficiently increasing values of the inductors 1202 and 1203, it is possible to increase an impedance to a ground plane and the differential-mode signal components id1 and id2 are transferred to output terminals OUT1 and OUT2.

[0278] Moreover, FIG. 12(c) shows the equivalent circuit of the phase circuit 1201 on common-mode signal components. As shown in FIG. 12(c), the connection point 1205 between the inductors 1202 and 1203 does not serve as a virtual ground point on the common-mode signal components ic1 and ic2. Therefore, by designing the inductor 1202 and a part of the capacitor 1204 and the inductor 1203 and a part of the capacitor 1204 so that they form a series resonant circuit at a predetermined frequency, common-mode signal components are shorted to ground planes and therefore, they are not transferred to the output terminal OUT1 or OUT2. In this case, a part of the capacitor 1204 denotes one hand equivalently becoming parallel connection (refer to FIG. 12(c)).

[0279] Furthermore, it is allowed that a phase circuit of the present invention has the configuration shown in FIGS. 13(a) to 13(c). FIGS. 13(a) to 13(c) are illustrations for explaining operations of the balanced high-frequency device of the present invention. As shown in FIG. 13(a), a phase circuit 1301 is constituted by capacitors 1302 and 1303 and an inductor 1304. As shown in FIG. 13(a), when a signal component i is input from an input terminal IN to the balanced device 1102, common-mode signal components ic1 and ic2 and differential-mode signal components id1 and id2 are output from the balanced device 1102. FIG. 13(b) shows the equivalent circuit of the phase circuit 1301 on the differential-mode signal components id1 and id2. As shown in FIG. 13(b), the connection point 1305 between the capacitors 1302 and 1303 serves as a virtual ground point on the differential-mode signal components id1 and id2. Therefore, by sufficiently decreasing values of the capacitors 1302 and 1303, it is possible to increase an impedance to a ground plane and the differential-mode signal components are transferred to the output terminals OUT1 and OUT2.

[0280] FIG. 13(c) shows the equivalent circuit of the phase circuit 1301 on the common-mode signal components ic1 and ic2. As shown in FIG. 13(c), the connection point 1305 between the capacitors 1302 and 1303 does not serve as a virtual ground point on the common-mode signal components id1 and ic2. Therefore, by designing the capacity 1302 and a part of the inductor 1304 and the capacitor 1303 and a part of the inductor 1304 so that they respectively form a series resonant circuit at a predetermined frequency, common-mode signal components are shorted to ground planes and therefore, they are not transferred to the output terminal OUT1 or OUT2. In this case, a part of the inductor 1304 denotes one hand equivalently becoming parallel connection (refer to FIG. 13(c)).

[0281] As described above, the balanced high-frequency device of the embodiment 5 of the present invention can reduce common-mode signal components by using three impedance elements as phase circuits and therefore, it is possible to realize a balanced high-frequency device excellent in balance-characteristic.

[0282] Moreover, in the case of this embodiment, the numbers of and configurations of inductors and capacitors serving as impedance element constituting a phase circuit are not restricted to the above case. Furthermore, though devices values of the impedance elements 1104 and 1105 are substantially equal to each other, it is not always necessary that the values are equal to each other but the values are optimally selected in accordance with a circuit configuration. Therefore, by using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained.

[0283] Furthermore, it is allowed that a phase circuit is formed on a circuit substrate by using a transmission line and a chip component or formed on a substrate with a balanced device mounted or in a substrate. Furthermore, it is allowed to form a part of the phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating the laminated device with a balanced high-frequency device of the present invention as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device.

[0284] In the case of this embodiment, it is described that an input terminal is the unbalanced type and an output terminal is the balanced type. However, it is also allowed that the input terminal is the balanced type and the output terminal is the unbalanced type. Furthermore, it is allowed that both the input terminal and output terminal are the balanced type.

[0285] Then, a balanced high-frequency device of embodiment 6 of the present invention is described below by referring to the accompanying drawings. A specific configuration of the balanced high-frequency device is described below on a case of using an surface acoustic wave filter as a balanced device. FIG. 14 shows a configuration of a balanced device of the present invention. In FIG. 14, a balanced high-frequency device 1401 is constituted by an surface acoustic wave filter 1402 and a phase circuit 1403 respectively serving as a balanced device. Moreover, in the case of the surface acoustic wave filter 1402, the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT1 and OUT2 serving as balanced input/output terminals. Moreover, the phase circuit 1403 is connected between the output terminals.

[0286] The surface acoustic wave filter 1402 is constituted on a piezoelectric substrate 1404 by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode) 1405, 1406, and 1407 and first and second reflector electrodes 1408 and 1409. One-hand electrode finger of the first IDT electrode 1405 is connected to the output terminal OUT1 and the other-hand electrode finger of the first IDT electrode 1405 is connected to the output terminal OUT2. Moreover, one-hand electrode fingers of the second and third IDT electrodes 1406 and 1407 are connected to the input terminal IN and the other-hand electrode fingers of them are grounded. By using the above configuration, it is possible to obtain a balanced high-frequency device having an unbalanced-balanced input/output terminal.

[0287] Then, specific characteristics of the balanced high-frequency device of this embodiment are described below. FIGS. 15(a) to 15(c) show characteristics of the balanced high-frequency device 1401 when using the phase circuit 603 shown in FIG. 6 as the phase circuit 1403. In this case, the transmission line 604 constituting the phase circuit 603 has substantially a length of λ/2 which corresponds to a phase shift of 180°. FIG. 15(a) shows a passing characteristic, FIG. 15(b) shows amplitude balance-characteristic of a pass band, and FIG. 15(c) shows a phase balance-characteristic of a pass band. The balance-characteristics in FIGS. 15(b) and 15(c) are greatly improved compared to conventional characteristics shown in FIG. 31 and are almost close to an ideal characteristic. Moreover, in the case of the passing characteristic, the attenuation at the high pass-band side is improved by approx. 5 dB.

[0288] Then, a case of changing the length of the transmission line 604 is evaluated. FIGS. 16(a) and 16(b) show balance-characteristics when changing the length of the transmission line 604. FIG. 16(a) shows amplitude balance-characteristics and FIG. 16(b) shows phase balance-characteristics. Moreover, symbols 1601 and 1602 denote the maximum value and minimum value of deteriorations in the amplitude balance-characteristic in a pass band of the surface acoustic wave filter of this embodiment. Symbols 1603 and 1604 denote the maximum value and minimum value of deteriorations in the phase balance-characteristics in the bass band of the surface acoustic wave filter of this embodiment. Furthermore, broken lines show the maximum value and minimum value of deteriorations in the balance-characteristics of a conventional surface acoustic wave filter. From FIGS. 16(a) and 16(b), it is found that the balance-characteristics are improved when the transmission line length ranges substantially between λ/4 and 3λ/4. Moreover, it is found that a more preferable balance-characteristic is obtained when the amplitude balance-characteristic ranges between substantially −5 dB and +5 dB and the phase balance-characteristic ranges between substantially −0.5° and +0.5° by keeping a phase angle in substantially the range between 3λ/8 and 5λ/8.

[0289] Then, characteristics when using a phase circuit of another configuration are shown. FIGS. 17(a) to 17(c) show characteristics of the balanced high-frequency device 1401 when using the phase circuit 901 shown in FIG. 9 as the phase circuit 1403. In this case, capacitances Cg1 and Cg2 of the capacitors 902 and 903 are substantially equal to each other so that impedances of the capacitors 902 and 903 respectively become 3 Ω at the frequency in a pass band. Moreover, the inductance Lb of the inductor 904 is designed so that parallel resonant frequencies between Cg1 and Lb/2 and between Cg2 and Lb/2 are kept in a pass band.

[0290] FIG. 17(a) shows a passing characteristic, FIG. 17(b) shows an amplitude balance-characteristic of a pass band, and FIG. 17(c) shows a phase balance-characteristic of a pass band. The balance-characteristics are greatly improved compared to those shown in FIG. 31 and are almost close to an ideal state. Moreover, in the case of the passing characteristics, the attenuation at the high pass-band side is improved by approx. 5 dB.

[0291] Then, a case in which impedances of the capacitors 902 and 903 are changed is evaluated. FIGS. 18(a) and 18(b) show balance-characteristics to standardized impedances obtained by dividing impedances of the capacitors 902 and 903 by the characteristic impedance of a terminal. In this case, because the characteristic impedance of a balanced output terminal is equal to substantially 50 Ω, it is assumed that the characteristic impedance of each terminal is equal to substantially 25 Ω. FIG. 18(a) shows amplitude balance-characteristics and FIG. 18(b) shows phase balance-characteristics. Moreover, symbols 1801 and 1802 denote the maximum value and minimum value of deteriorations in the amplitude balance-characteristics in the pass band of the surface acoustic wave filter of this embodiment and 1803 and 1804 denote the maximum value and minimum value of deteriorations in the phase balance-characteristics in the pass band of the surface acoustic wave filter of this embodiment. From FIGS. 18(a) and 18(b), it is found that the balance-characteristics are improved when standardized impedances are equal to or less than 2.

[0292] Then, characteristics when using a phase circuit of another configuration are described below. FIGS. 19(a) to 19(c) show characteristics of the balanced high-frequency device 1401 when using the phase circuit 1001 shown in FIG. 10 as the phase circuit 1403. In this case, inductance values Lg1 and Lg2 of the inductors 1002 and 1003 are substantially equal to each other and the inductors 1002 and 1003 are designed so that impedances of the inductors are respectively equal to substantially 3 Ω at the frequency in a pass band. Moreover, the capacitance Cb of the capacitor 1004 is designed so that parallel resonant frequencies between Lg1 and 2Cb and between Lg2 and 2Cb are kept in a pass band.

[0293] FIG. 19(a) shows a passing characteristic, FIG. 19(b) shows an amplitude balance-characteristic of a pass band, and FIG. 19(c) shows a phase balance-characteristic of a pass band. The balance-characteristics are greatly improved compared to conventional characteristics shown in FIG. 31 and are almost close to an ideal state. Moreover, in the case of the passing characteristic, the attenuation at the high pass band side is improved by approx. 5 dB.

[0294] Then, a case is evaluated in which impedances of the inductors 1002 and 1003 are changed. FIGS. 20(a) and 20(b) show balance-characteristics to standardized impedances obtained by dividing the impedances of the inductors 1002 and 1003 by the characteristic impedance of a terminal. In this case, because the characteristic impedance of a balanced output terminal is substantially equal to 50 Ω, the characteristic impedance of each terminal is set to substantially 25 Ω. FIG. 20(a) shows amplitude balance-characteristics and FIG. 20(b) shows phase balance-characteristics. Moreover, symbols 2001 and 2002 denote the maximum value and minimum value of deteriorations in the amplitude balance-characteristics in the pass band of the surface acoustic wave filter of this embodiment and 2003 and 2004 denote the maximum value and minimum value of deteriorations in the phase balance-characteristics in the bass band of the surface acoustic wave filter of this embodiment.

[0295] From FIG. 20, it is found that the phase balance-characteristics are improved when the standardized impedance is substantially 2 or less. Moreover, the amplitude balance-characteristics are improved when the standardized impedance is substantially 0.5 or less. Therefore, it is preferable to keep the standardized impedance at substantially 2 or less. More preferably, by preferably keeping the standardized impedance at substantially 0.5 or less, it is possible to improve the balance-characteristics.

[0296] As described above, in the case of the balanced high-frequency device 1401 of the embodiment 6 of the present invention, it is possible to reduce common-mode components by using three impedance elements as phase circuits and thereby realize a balanced high-frequency device excellent in balance-characteristic.

[0297] Moreover, though this embodiment is described by using a transmission line as a phase circuit, it is preferable that the transmission line substantially has a length of λ/2. This is because the phase circuit more frequently operates as an inductor or capacitor as the transmission-line length is shifted from λ/2 and the impedance of the pass-band frequency 2102 when viewing a balanced device from the output-terminal side is shifted from a matching state. For example, when the length of a transmission line is equal to 3λ/8, the impedance of the passing band 2101 becomes inductive as shown in FIG. 21(a). In this case, as shown in FIG. 22, it is only necessary to connect the transmission line 604 as a phase circuit and a capacitor 2202 serving as a matching circuit between output terminals of a phase circuit 2201 in parallel. As shown in FIG. 21(b), by using the above configuration, the impedance of a pass-band vicinity 2102 when viewing a balanced device from the output-terminal side becomes the center of Smith chart and it is possible to realize impedance matching. Thus, it is allowed to constitute a phase circuit so as to include a matching circuit for performing impedance matching.

[0298] Moreover, the fact that the length of a transmission line is equal to 3λ/8 is equivalent to the fact that the phase angle is 135° and approaches 180° by adding the above matching circuit and the length of the transmission line substantially approaches λ/2. Therefore, by adding the matching circuit, it is possible to decrease the length of the transmission line and downsize the configuration.

[0299] In the case of this embodiment, the phase circuit is constituted by using the transmission line or three impedance elements. However, the configuration of a phase circuit is not restricted to the above case. Moreover, the numbers of and configurations of inductors and capacitors serving as impedance elements are not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained.

[0300] Moreover, it is allowed to form a phase circuit on a circuit substrate by using a transmission line and a chip component. It is also allowed to constitute a phase circuit on a substrate with a balanced device mounted or in a package. Moreover, it is allowed to form a part of a phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating a balanced high-frequency device of the present invention with the laminated device as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device.

[0301] Though it is described that an input terminal is the unbalanced type and an output terminal is the balanced type in the case of this embodiment, it is allowed that the input terminal is the balanced type and the output terminal is the unbalanced type or both the input terminal and output terminal are the balanced type.

[0302] A balanced high-frequency device of embodiment 7 of the present invention is described below by referring to the accompanying drawings. A specific configuration when a matching circuit is included in a phase circuit is described below. FIG. 23(a) shows a configuration of the balanced high-frequency device of the embodiment 7 of the present invention. In FIG. 23(a), a balanced high-frequency device 2301 is constituted by a balanced device 2302 and a phase circuit 2303. Moreover, in the balanced device 2302, the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT1 and OUT2 serving as balanced input/output terminals. Moreover, the phase circuit 2303 is connected between the output terminals.

[0303] The phase circuit 2303 is constituted by capacitors 2304 and 2305 and an inductor 2306 serving as impedance elements and an inductor 2307 serving as a matching circuit. In this case, the output terminals OUT1 and OUT2 are grounded through the capacitors 2304 and 2305 respectively, the inductor 2306 is connected between the output terminals, and the phase circuit 2303 is connected between the output terminals. Moreover, the inductor 2307 serving as a matching circuit is included in the phase circuit 2303.

[0304] The inductor 2306 forms a virtual ground point 2308 on a differential-mode signal component. Therefore, the capacitor 2304 and a part of the inductor 2306 form a parallel resonant circuit to a ground plane at the output terminal OUT1 and the capacitor 2305 and a part of the inductor 2306 form a parallel resonant circuit to a ground plane at the output terminal OUT2. By designing parallel resonant frequencies of the parallel resonant circuits so that they are kept in a passing band or nearby the passing band, the impedance of a differential-mode signal component at a predetermined frequency approaches infinity to a ground plane and transferred to an output terminal without being shorted to the ground plane. That is, operations substantially same as those shown in FIG. 7(c) are executed on the differential-mode signal component.

[0305] Moreover, the inductor 2306 does not form a virtual ground point on an common-mode signal component. Therefore, by designing impedances of the capacitors 2304 and 2305 serving as impedance elements arranged between the balanced input/output terminals OUT1 and OUT2 and ground planes to sufficiently small values, the common-mode signal component is shorted to a ground plane and thereby, it is not transferred to a balanced input/output terminal.

[0306] As described above, in the case of the phase circuit 2303 of this embodiment, a resonant circuit at a predetermined frequency is constituted by the capacitors 2304 and 2305 and the inductor 2306 and the inductor 2307 serving as a matching circuit is included. Also in this case, common-mode signal components are reduced and it is possible to realize a balanced high-frequency device having excellent balance-characteristics.

[0307] Moreover, it is possible to incorporate the inductor 2307 into the inductor 2306. That is, it is enough to use a combined inductance 2309 of the inductors 2306 and 2307. In this case, because the inductors 2306 and 2307 are connected in parallel, the expression Lt=(Lb×Lm)/(Lb+Lm) is effectuated when assuming inductances of the inductors 2306 and 2307 and combined inductor 2309 as Lb, Lm, and Lt respectively. Thus, it is possible to decrease values of the inductances. Moreover, it is possible to decrease the number of devices and downsize a circuit configuration.

[0308] In this case, however, the meaning of a predetermined frequency differs. That is, when assuming capacitances of the capacitors 2304 and 2305 as Cg1 and Cg2, parallel resonant frequencies f1 and f2 of differential-mode signal components at each output terminal in a matching state formed by the capacitors 2304 and 2305 and inductor 2306 become f1=1/{2π×√(Lb/2)×√(Cg1)} and f2=1/{2π×√(Lb/2)×√(Cg2)}. In this case, by including the inductor 2307 serving a matching circuit, the whole parallel resonant frequencies f1t and f2t become f1t=1/{2π×√(Lt/2)×(Cg1)} and f2t=1/{2π×√(Lt/2)×√(Cg2)} and thus, they are apparently shifted from predetermined frequencies.

[0309] That is, the whole parallel resonant frequency of the phase circuit 2303 is shifted from a pass band or the vicinity of the pass band by a value equivalent to the inductor Lm. However, the effect that common-mode signal component can be reduced is the same when the capacitor 2304 and a part of the inductor 2306 form a parallel resonant circuit to a ground plane at the output terminal OUT1 and the capacitor 2305 and a part of the inductor 2306 form a parallel resonant circuit to a ground plane in a matching state and the impedance to ground planes of the capacitors 2304 and 2305 are sufficiently small. In this case, a part of the inductor 2306 denotes a range up to a virtual ground plane.

[0310] However, the circuit configuration of this embodiment is not restricted to the above case. As long as operations of a matching circuit and operations of a resonant circuit are substantially the same as the case of the present invention, it is possible to realize a balanced high-frequency device having excellent balance-characteristics similarly to the case of the present invention.

[0311] Moreover, though values Cg1 and Cg2 of capacitors serving as impedance elements are assumed to be substantially the same and values Lg1 and Lg2 of inductors serving as impedance elements are assumed to be substantially the same, it is not always necessary that these values are the same but they are optimally selected in accordance with a circuit configuration.

[0312] A balanced high-frequency device of embodiment 8 of the present invention is described below by referring to the accompanying drawings. Specific characteristics of the balanced high-frequency device are described below on a case of using an surface acoustic wave filter as a balanced device. FIG. 24 shows a configuration of a balanced high-frequency device 2401 of the present invention. In FIG. 24, the balanced high-frequency device 2401 is constituted by an surface acoustic wave filter 2402 serving as a balanced device and a phase circuit 2403. Moreover, in the case of the surface acoustic wave filter 2402, the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT1 and OUT2 serving as balanced input/output terminals. Moreover, the phase circuit 2403 is connected between the output terminals.

[0313] The surface acoustic wave filter 2402 is formed on a piezoelectric substrate 2404 by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode) 2405, 2406, and 2407 and first and second reflector electrodes 2408 and 2409. The first IDT electrode 2405 is divided into two divided IDT electrodes and one-hand electrode fingers of the first and second divided IDT electrodes 2410 and 2411 are connected to the output terminals OUT1 and OUT2. The other-hand electrode fingers of the first and second divided IDT electrodes 2410 and 2411 are electrically connected and virtually grounded. Moreover, one-hand electrode fingers of the second and third IDT electrodes 2406 and 2407 are connected to the input terminal IN and the other-hand electrode fingers of them are grounded. By using the above configuration, it is possible to obtain a balanced high-frequency device having an unbalance-balanced input/output terminal.

[0314] Also in the case of the balanced high-frequency device 2401 of the embodiment 8 of the present invention, it is possible to reduce common-mode signal components by using the phase circuit 2403 and realize a balanced high-frequency device excellent in balance-characteristic.

[0315] In the case of this embodiment, it is also allowed to constitute a phase circuit by using a transmission line or three impedance elements. Moreover, a configuration of the phase circuit is not restricted to the above one. By using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained. Moreover, the numbers of and configurations of inductors and capacitors serving as impedance elements are not restricted to the above mentioned. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained.

[0316] Moreover, it is allowed to form a phase circuit on a circuit substrate by using a transmission line and a chip component or form the phase circuit on a substrate with a balanced device mounted or in a package. Furthermore, it is allowed to form a part of the phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating the laminated device with a balanced high-frequency device of the present invention as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device.

[0317] Though it is described that an input terminal is the unbalanced type and an output terminal is the balanced type in the case of this embodiment, it is allowed that the input terminal is the balanced type and the output terminal is the unbalanced type. Moreover, it is allowed that both the input and output terminals are the balanced type.

[0318] A balanced high-frequency device of embodiment 9 of the present invention is described below by referring to the accompanying drawings. Specific characteristics of the balanced high-frequency device are described below on a case of using an surface acoustic wave filter as a balanced device. FIG. 25 shows a configuration of a balanced high-frequency device 2501 of the embodiment 9 of the present invention. In FIG. 25, the balanced high-frequency device 2501 is constituted by an surface acoustic wave filter 2502 serving as a balanced device and a phase circuit 2503. Moreover, in the case of the surface acoustic wave filter 2502, the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT1 and OUT2 serving as balanced terminals. Furthermore, the phase circuit 2503 is connected between the output terminals.

[0319] The surface acoustic wave filter 2502 is formed on a piezoelectric substrate 2504 by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode) 2505, 2506, and 2507 and first and second reflector electrodes 2508 and 2509. One-hand electrode finger of the first IDT electrode is connected to the input terminal IN and the other-hand electrode finger of it is grounded. One-hand electrode fingers of the second and third IDT electrodes 2506 and 2507 are connected to the output terminals OUT1 and OUT2 and the other-hand electrode fingers of them are grounded. By using the above configuration, a balanced high-frequency device having an unbalanced-balanced input/output terminal is obtained.

[0320] Also in the case of the balanced high-frequency device 2501 of the present invention, it is possible to reduce common-mode signal components by using the phase circuit 2503 and therefore, realize a balanced high-frequency device excellent in balance-characteristic.

[0321] In the case of this embodiment, a phase circuit is provided by using a transmission line or three impedance elements. Moreover, a configuration of the phase circuit is not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained. Furthermore, the numbers of and configurations of inductors and capacitors serving as impedance elements are not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained.

[0322] Furthermore, a phase circuit may be formed on a circuit substrate by using a transmission line or a chip component or integrate the phase circuit on a substrate with a balanced device mounted or in a package. Furthermore, a part of the phase circuit may be formed in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by forming the laminated device so as to have another circuit function and integrating a balanced high-frequency device of the present invention with the laminated device as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device.

[0323] Though it is described that an input terminal is the unbalanced type and an output terminal is the balanced type in the case of this embodiment, the input terminal may be the balanced type and the output terminal the unbalanced type. Moreover, both the input and output terminals may be the balanced type.

[0324] A balanced high-frequency device of embodiment 10 of the present invention is described below by referring to the accompanying drawings. FIG. 26 shows a configuration of a balanced high-frequency device 2601 of the embodiment 10 of the present invention. For FIG. 26, a specific configuration of the balanced high-frequency device is described on a case of using a semiconductor device as the balanced device. In FIG. 26, the balanced high-frequency device 2601 is constituted by a semiconductor device 2602 serving as a balanced device and phase circuits 2603 and 2608. Moreover, in the case of the semiconductor device 2602, input-side terminals are input terminals IN1 and IN2 serving as balanced input/output terminals and output-side terminals are output terminals OUT1 and OUT2 serving as balanced terminals. Furthermore, the phase circuit 2603 is connected between the input terminals and the phase circuit 2608 is connected between the output terminals.

[0325] Then, a configuration of the semiconductor device 2602 is described below. Symbols 2604a, 2604b, 2605a, and 2605b denote bipolar transistors and 2606a and 2606b denote inductors. The input terminal IN1 is connected to the base of the bipolar transistor 2604a through a DC-cut capacitor 2607a and the input terminal IN2 is connected to the base of the bipolar transistor 2604b through a DC-cut capacitor 2607b. Collectors of the bipolar transistors 2604a and 2604b are connected to emitters of the bipolar transistors 2605a and 2605b respectively and collectors of the bipolar transistors 2605a and 2605b are connected to the output terminals OUT1 and OUT2 through DC-cut capacitors 2609a and 2609b respectively. Emitters of the bipolar transistors 2604a and 2604b are grounded through the inductors 2606a and 2606b respectively. A bias circuit 2610 supplies a bias current to bases of the bipolar transistors 2604a and 2604b. A bias circuit 2611 supplies a bias current to bases of the bipolar transistors 2605a and 2605b. A power-source voltage Vcc is supplied to collectors of the bipolar transistors 2605a and 2605b through choke inductors 2912a and 2912b respectively. By using the above configuration, a balanced semiconductor device operates as an amplifier.

[0326] Also in the case of the balanced high-frequency device 2601 of the embodiment 10 of the present invention, it is possible to reduce common-mode signal components by using the phase circuits 2603 and 2608 and therefore, realize a balanced high-frequency device excellent in balance-characteristic.

[0327] In this embodiment, a phase circuit may be formed by using a transmission line or three impedance elements. Moreover, a configuration of the phase circuit is not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained. Furthermore, the numbers of and configurations of inductors and capacitors serving as impedance elements are not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained.

[0328] A phase circuit may be formed on a circuit substrate by using a transmission line or a chip component or integrate the phase circuit on a substrate with a balanced device mounted or in a package. Moreover, a part of the phase circuit may be formed in a laminated device by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by forming the laminated device so as to have another circuit function and integrating a balanced high-frequency device of the present invention with the laminated device as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device.

[0329] Furthermore, in the case of this embodiment, it is described that input and output terminals are the balanced type. However, either of the input and output terminals may be the unbalanced type and the other of them is the balanced type.

[0330] Furthermore, in the case of this embodiment, a semiconductor device is formed by four bipolar transistors. However, a configuration of the semiconductor device is not restricted to the above case.

[0331] Furthermore, for this embodiment, a case is described in which the semiconductor device 2602 is an amplifier. However, the semiconductor device 2602 is not restricted to an amplifier. The semiconductor device 2602 may be a mixer or oscillator. In short, the semiconductor device 2602 is permitted as long as it is a semiconductor device having a balanced terminal.

[0332] A balanced high-frequency circuit of embodiment 11 of the present invention is described below by referring to the accompanying drawings. FIG. 27 is a block diagram of a balanced high-frequency circuit 2701 using a balanced device of the present invention. In FIG. 27, an output signal output from a transmitting circuit is transmitted from an antenna 2705 through a transmitting amplifier 2702, a transmitting filter 2703 and a switch 2704. Moreover, an input signal received through the antenna 2705 is input to a receiving circuit through the switch 2704, a receiving filter 2706, and a receiving amplifier 2707. In this case, because the transmitting amplifier 2702 is the balanced type and the switch 2704 is the unbalanced type, the transmitting filter 2703 is constituted so as to have an unbalanced-balanced input/output terminal. Furthermore, because the receiving amplifier 2707 is the balanced type and the switch 2704 is the unbalanced type, the receiving filter 2706 is constituted so as to have an unbalanced-balanced input/output terminal.

[0333] By applying a balanced device of the present invention to the transmitting filter 2703 or receiving filter 2706 of the balanced high-frequency circuit 2701 and a balanced high-frequency device of the present invention to the transmitting amplifier 2702 or receiving amplifier 2707, it is possible to prevent modulation accuracy deterioration at the time of transmission due to deterioration of a balance-characteristic and sensitivity deterioration at the time of reception due to deterioration of a balance-characteristic and realize a high-performance balanced high-frequency circuit.

[0334] Moreover, when the switch 2704 is the balanced type and the transmitting amplifier 2702 or receiving amplifier 2707 is the unbalanced type, the same advantage is obtained by replacing balanced-type and unbalanced-type input/output terminals of the transmitting filter 2703 or receiving filter 2706 with each other.

[0335] Though means of switching transmission and reception is described by using the switch 2704 in the case of the balanced high-frequency circuit 2701, the means may use a shared unit.

[0336] Moreover, a phase circuit of the present invention may be formed on a circuit substrate in the case of the balanced high-frequency circuit of this embodiment. For example, in FIG. 27, by forming the phase circuit between balanced transmission lines 2708 and 2709 on the circuit substrate, it is possible to prevent balance-characteristic deterioration due to the crosstalk of common-mode signal components and realize a excellent balanced high-frequency circuit.

[0337] Furthermore, embodiments of the present invention are described by using an surface acoustic wave filter or semiconductor device as a balanced high-frequency device. However, the present invention can be applied not only to the above case but also to another device which balance-operates.

[0338] Furthermore, on a device for handling a high-frequency signal, parasitic components increase as frequency rises, common-mode signal component increase due to crosstalk, and deterioration of balance-characteristics increases. Therefore, advantages of a balanced high-frequency device of the present invention increase as a frequency rises and it is possible to downsize a transmission line and an impedance element for forming a phase circuit.

[0339] As described above, the present invention makes it possible to provide a balanced high-frequency device having preferable balance-characteristics, balanced high-frequency circuit, phase circuit, and balance-characteristics improving method.