Hybrid balun apparatus and receiver comprising the same

[0001] This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 10-2006-0035056 filed in Korea on Apr. 18, 2006, the entire contents of which are hereby incorporated by reference.

[0002] 1. Field of the Invention

[0003] The present invention relates to a receiver, and more particularly, to a balun apparatus and a receiver comprising the same.

[0004] 2. Description of the Background Art

[0005] A circuit for processing a differential signal is essential in a highly integrated receiver to reduce the effects of external noise and switching noise generated in an inside digital circuit.

[0006] Therefore, it requires an element that transforms an input signal received through an antenna to a differential signal. Such an element is a balun.

[0007] As a typical balun, a passive balun using a transformer and an active balun using a transistor amplifier were introduced.

[0008] FIG. 1 shows a passive balun circuit in accordance with the related art.

[0009] As shown in FIG. 1, the passive balun circuit according to the related art is embodied by comprising a transformer. The passive balun circuit transforms an input signal (Single-ended; V_IN) applied at the primary coil of the transformer 100 having L_p inductance to an in-phase output signal (V_OUT+) and an inverse-phase output signal (V_OUT−) through the secondary coil of the transformer 100 having L_s inductance.

[0010] The passive balun circuit has an advantage that small amplitude error and small phase error can be achieved for the in-phase output signal (V_OUT+) and the inverse-phase output signal (V_OUT−).

[0011] However, the power of the input signal is weakened because of an imperfect coupling coefficient (k-factor) that is a typical characteristic of the practical transformer 100 in the passive balun circuit. Thus, the power of the in-phase output signal (V_OUT+) and an inverse-phase output signal (V_OUT−) become weakened compared to that of the input signal. Usually in practice, the k-factor ranges from 0.5 to 0.8 in a real environment whereas an ideal k-factor is 1.

[0012] Therefore, the passive balun circuit cannot fully transfer the power of the input signal to the output terminals. That is, the passive balun circuit suffers the power loss due to the imperfect coupling coefficient. Consequently, the signal attenuation occurs through the balun, and it will directly degrade the noise figure and the power gain of the total receiving terminal since it is the most front-end element in the total receiving terminal.

[0013] FIG. 2 shows an active balun circuit in accordance with the related art.

[0014] Referring to FIG. 2, the active balun circuit 200 according to the related art comprises an input unit 210, a feed-back unit 220, and an output unit 230.

[0015] The input unit 210 is embodied as a differential circuit that comprises a first transistor NM_2a and a second transistor NM_2b. And the gate terminal of the second transistor NM_2b is connected to the feed-back unit 220. The input signal V_IN is applied to the gate terminal of the first transistor NM_2a and the output signals V_OUT+ and V_OUT− are extracted differentially.

[0016] In FIG. 2, the input unit 210 is embodied as a common source circuit. However, the input unit 210 can be also embodied as a common gate circuit.

[0017] The active balun circuit 200 has drawbacks as follows. The active balun circuit 200 consumes greater power due to the transistors involved, and usually operates only in a narrow band due to the resonance circuit 220.

[0018] Accordingly, the present invention is conceived in order to solve the problems and disadvantages of the background art. It is an object of the present invention to provide a balun apparatus providing highly symmetrically balanced signals, consuming less power, having a low noise factor, having less power loss, and having high linearity.

[0019] It is another object of the present invention to provide a balun apparatus suitable for wideband operation.

[0020] It is still another object of the present invention to provide a wideband receiver having a simple structure, consuming low power, having a low noise factor, having high gain, and having high linearity, based on the said balun apparatus.

[0021] In accordance with an aspect of the present invention, a hybrid balun apparatus comprises a passive unit, a first active unit, and a second active unit. The passive unit receives an input signal, and outputs an in-phase signal having an identical phase compared to the input signal and an inverse-phase signal having an inverse phase compared to the input signal. The first active unit compensates the in-phase output signal of the passive unit corresponding to the input signal. The second active unit compensates the inverse-phase output signal of the passive unit in response to the input signal. The first active unit and the second active unit are voltage amplifiers to generate the compensating signals.

[0022] In accordance with another aspect of the present invention, a receiver comprises a passive unit, a first active unit, and a second active unit. The passive unit comprises a primary coil and a secondary coil. An input signal is applied to the primary coil. The secondary coil outputs an in-phase signal and an inverse-phase signal through an in-phase output terminal and an inverse-phase output terminal, respectively, in response to the input signal applied to the primary coil. Herein, the in-phase signal has an identical phase compared to the input signal, and the inverse-phase signal has an inverted phase compared to the input signal. The first active unit comprises a first transistor for outputting an in-phase compensating signal having an identical phase compared to the in-phase signal in response to the input signal. The second active unit comprises a second transistor for outputting an inverse-phase compensating signal having an identical phase compared to the inverse-phase signal in response to the input signal.

[0023] The first transistor may be configured as a source-follower amplifier, and the second transistor may be configured as a common-source amplifier.

[0024] The first active unit and the second active unit may be combined to be a single differential amplifier that can differentially amplify the input signal to create the in-phase and inverse-phase compensating signals.

[0025] The secondary coil may be tapped in its center terminal.

[0026] The in-phase signal output terminal of the secondary coil and the output terminal of the first transistor may be connected to the in-phase output terminal, and the inverse-phase signal output terminal of the secondary coil and the output terminal of the second transistor may be connected to the inverse-phase output terminal.

[0027] In accordance with still another aspect of the present invention, a receiver comprises a hybrid balun apparatus.

[0034] Preferred embodiments of the present invention will be described in a more detailed manner with reference to the drawings.

[0035] Hereinafter, a balun apparatus in accordance with the present invention and a receiver comprising the same will be described in detail with reference to the drawings in accordance with an embodiment of the present invention.

[0036] FIG. 3 is a block diagram illustrating a hybrid balun in accordance with an embodiment of the present invention.

[0037] As shown in FIG. 3, the hybrid balun according to the present embodiment comprises a passive unit 310, a first active unit 320 and a second active unit 330.

[0038] The input terminal of the passive unit 310 is connected to a first node {circle around (1)}, the in-phase output terminal of the passive unit 310 is connected to a second node {circle around (2)}, and the inverse-phase output terminal of the passive unit 310 is connected to a third node {circle around (3)}.

[0039] The input terminal of the first active unit 320 is connected to a first node {circle around (1)}, and the output terminal of the first active unit 320 is connected to a second node {circle around (2)}.

[0040] The input terminal of the second active unit 330 is connected to a first node {circle around (1)}, and the output terminal of the second active unit 330 is connected to a third node {circle around (3)}.

[0041] An input signal (single-ended: V_IN) is applied to a first node {circle around (1)}. An in-phase signal V_OUT+ is taken at a second node {circle around (2)}, and an inverse-phase output signal V_OUT− is taken at a third node {circle around (3)}.

[0042] The passive unit 310 receives the input signal V_IN and outputs an in-phase signal 322 that has an identical phase compared to the input signal V_IN.

[0043] The first active unit 320 receives the input signal V_IN and outputs an in-phase compensating signal 321 that has an identical phase compared to the input signal V_IN.

[0044] The in-phase compensating signal 321 is a signal for compensating the loss of the in-phase signal 322 caused by the passive unit 310. The in-phase compensating signal 321 has an identical phase and different amplitude compared to the in-phase signal 322.

[0045] According to the structure described above, the in-phase output signal V_OUT+ is formed by adding the in-phase signal 322 of the passive unit 310 applied to a second node {circle around (2)} and the in-phase compensating signal 321 of the first active unit 320 applied to a second node {circle around (2)}.

[0046] The passive unit 310 receives the input signal V_IN and outputs an inverse-phase signal 332 that has an inversed phase compared to the input signal V_IN.

[0047] The second active unit 330 receives an input signal V_IN and outputs an inverse-phase compensating signal 331 having an inversed phase compared to the input signal V_IN.

[0048] The inverse-phase compensating signal 331 is a signal for compensating the loss of the inverse-phase signal 332 caused by the passive unit 310. The inverse-phase compensating signal 331 has an identical phase and different amplitude compared to the inverse-phase signal 332.

[0049] According to the structure described above, the inverse-phase output signal V_OUT− is formed by adding the inverse-phase signal 332 of the passive unit 310 applied to a third node {circle around (3)} and the inverse-phase compensating signal 331 of the second active unit 330 applied to a third node {circle around (3)}.

[0050] That is, the first active unit 320 and the second active unit 330 behaves as a balanced circuit that simultaneously receives the input signal V_IN, differentially amplifies them and outputs the in-phase compensating signal 321 and the inverse-phase compensating signal 331.

[0051] The internal circuits of the passive unit 310, the first active unit 320 and the second active unit 330 will be described in detail with reference to FIGS. 4A through 4C.

[0052] FIGS. 4A through 4C illustrate a hybrid balun apparatus in accordance with an embodiment of the present invention.

[0053] As shown in FIG. 4A, the hybrid balun apparatus according to the present embodiment includes a passive unit 310, a first active unit 320 and a second active unit 330.

[0054] Hereinafter, the structure of the hybrid balun apparatus 300 according to the present embodiment will be described.

[0055] The passive unit 310 comprises a transformer 311 and a fifth capacitor C₃₃ for bypassing AC (alternating current) signal.

[0056] The transformer 311 comprises a primary coil and a secondary coil. A center tap terminal is formed at the middle of the second coil for balanced output signals.

[0057] The first active unit 320 comprises a first transistor NM_3a and a first capacitor C₃₁₊.

[0058] The second active unit 330 comprises a second transistor NM_3b and a second capacitor C₃₁₋.

[0059] The hybrid balun apparatus 300 comprises a third capacitor C₃₂₊ for removing the DC (direct current) component of the in-phase output signal V_OUT+, a fourth capacitor C₃₂₋ for removing the DC component of the inverse-phase output signal V_OUT−, and a fifth capacitor C₃₃ for bypassing AC component from the tap terminal of the transformer 311 to the ground.

[0060] Hereinafter, the connecting relations of constitutional elements in the hybrid balun apparatus 300 according to the present embodiment will be described.

[0061] The one end of the primary coil of the transformer 311 is connected to a first node {circle around (1)}, and the other end of the primary coil is connected to the ground. The in-phase output terminal of the secondary coil of the transformer 311 is connected to a second node {circle around (2)}, and an inverse-phase output terminal of the secondary coil is connected to a third node {circle around (3)}. The center tap terminal of the inverse-phase output terminal is connected to a sixth node {circle around (6)}.

[0062] The one end of the fifth capacitor C₃₃ is connected to a sixth node (, and the other end of the fifth capacitor C33 is connected to the ground.

[0063] The one end of the first capacitor C31+ is connected to a first node (, and other end of the first capacitor C31+ is connected to a fourth node (.

[0064] The gate terminal of the first transistor NM_3a is connected to a fourth node {circle around (4)}. A power supply voltage V_DD is connected to the drain terminal of the first transistor NM_3a, and the source terminal of the first transistor NM_3a is connected to a second node {circle around (2)}.

[0065] The one end of a third capacitor C₃₂₊ is connected to a second node {circle around (2)}, and the other end of the third capacitor C₃₂₊ outputs an in-phase output signal V_OUT+.

[0066] The one end of a second capacitor C₃₁₋ is connected to a first node {circle around (1)}, and the other end of the second capacitor C₃₁₋ is connected to a fifth node 5.

[0067] The gate terminal of the second transistor NM_3b is connected to a fifth node 5. The drain terminal of the second transistor NM_3b is connected to a third node {circle around (3)}, and the source terminal of the second transistor NM_3b is connected to the ground.

[0068] The one end of the fourth capacitor C₃₂₋ is connected to a third node {circle around (3)}, and the other end of the fourth capacitor C₃₂₋ outputs an inverse-phase output signal V_OUT−.

[0069] Hereinafter, the operations of the hybrid balun apparatus 300 according to the present embodiment will be described with reference to FIGS. 4B and 4C.

[0070] When an input signal V_IN is applied to a first node {circle around (1)}, the supplied input signal V_IN is applied simultaneously to the input terminal of the passive unit 310, the input terminal of the first active unit 320, and the input terminal of the second active unit 330.

[0071] When the input signal is applied to the one end of the primary coil of the transformer 311 of the passive unit 310, the secondary coil that is magnetically coupled to the primary coil becomes excited, and the output signal is generated at the secondary coil.

[0072] Therefore, the transformer 311 outputs the in-phase signal 322 that has an identical phase compared to the input signal V_IN to a second node {circle around (2)} through the in-phase output terminal of the secondary coil along an in-phase signal path 322a.

[0073] Also, the transformer 311 outputs an inverse-phase signal 332 that has an inverse phase compared to the input signal V_IN to the third node {circle around (3)} through an inverse-phase output terminal of the secondary coil along an inverse-phase signal path 332a.

[0074] However, the transformer 311 usually causes signal power loss during the signal conversion process from the single-ended input signal V_IN to the differential signals 322 and 332.

[0075] The transformer 311 has such a characteristic because a coupling coefficient (k-factor) of the transformer 311 is typically less than 1.

[0076] In order to overcome such a drawback, the hybrid balun apparatus 300 according to the present embodiment comprises the first active unit 320 for generating an in-phase compensating signal 321 that compensates the in-phase signal 322 of the transformer 311, and a second active unit 330 for generating an inverse-phase compensating signal 331 that compensates the inverse-phase signal 332 of the transformer 311.

[0077] The first active unit 320 removes the DC component of the input signal V_IN applied to the input terminal of the first active unit 320 by using the first capacitor C₃₁₊.

[0078] The DC-removed input signal V_IN is applied to the gate terminal of the first transistor NM_3a along the in-phase compensating signal path 321a. And the in-phase compensating signal 321 is generated with an identical phase and a smaller amplitude compared to the input signal V_IN, and supplied to the second node {circle around (2)}.

[0079] That is, the in-phase output signal V_OUT+ is formed of the sum of the in-phase signal 322, which is provided through the in-phase signal path 322a of the passive unit 310, and the in-phase compensating signal 321, which is provided through the in-phase compensating signal path 321a of the first active unit 320.

[0080] According to the structure described above, the loss of the input signal V_IN at the passive unit 10 is compensated by the first active unit 320 in the hybrid balun apparatus 300 according to the present embodiment.

[0081] Using same method, the second active unit 330 removes the DC component of the input signal V_IN supplied to the input terminal of the second active unit 330 by using the second capacitor C₃₁₋.

[0082] The DC-removed input signal V_IN is applied to the gate terminal of the second transistor NM_3b along the inverse-phase compensating signal path 331a. And the inverse-phase compensating signal 331 is generated with an inverse-phase and a smaller amplitude compared to the input signal V_IN, and supplied to the third node {circle around (3)}.

[0083] That is, the inverse-phase output signal V_OUT− is formed of the sum of the inverse-phase signal 332, which is provided through the inverse-phase signal path 332a of the passive unit 310, and the inverse-phase compensating signal 331, which is provided through the inverse-phase compensating signal path 331a of the second active unit 330.

[0084] According to the structure described above, the loss of the input signal V_IN at the passive unit 310 is compensated by the second active unit 330 in the hybrid balun apparatus 300 according to the present embodiment.

[0085] Also, the hybrid balun apparatus 300 according to the present embodiment has less power consumption, wideband characteristic, and better linearity compared to the conventional active balun due to its simple circuit structure and no resonating element. Also, the hybrid balun apparatus 300 according to the present embodiment has higher power gain and lower noise factor compared to the conventional passive balun due to the active compensating parts.

[0086] Also, the first active unit 320 and the second active unit 330 can be embodied as a fully symmetric differential amplifier circuit that provides the in-phase compensating signal 321 and the inverse-phase compensating signal 331 by differentially amplifying the input signal V_IN.

[0087] Table 1 compares the characteristics of a passive balun circuit and a hybrid balun apparatus 300 according to the present invention.

[0088]

	TABLE 1
	Passive	Hybrid
Operating frequency	2.4 GHz	2.4 GHz
Gain error/Phase error	0.07 dB/	0.57 dB/1.93°
	2.79°
Maximum gain (+S11 < −18 dB)	−2.75 dB	0.45 dB
Minimum noise factor (*S11 < −18 dB)	2.75 dB	2.4 dB
Input 1-dB compression point	Infinity	+12 dBm/+15.4
(P1dB)/Input referred third-order		dBm
intercept point (IIP3)
DC power consumption	0 mW	1.2 V × 0.68 mA =
		0.82 mW

[0089] Table 1 shows the representative results of prototype measurements of a hybrid balun according to the present embodiment that is manufactured using a 0.18 μm radio frequency (RF) complementary metal-oxide semiconductor (CMOS) manufacturing process. As shown in Table 1, the hybrid balun apparatus according to the present invention has about 0.57 dB amplitude error and about 1.93° phase error at 2.4 GHz. The gain of the hybrid balun is improved as much as about 3.2 dB, and the noise factor is improved as much as about 0.35 dB compared to the conventional passive balun.

[0090] Also, the hybrid balun apparatus 300 according to the present embodiment consumes about 0.68 mA at about 1.2V, and the overall power consumption is about 0.82 mW.

[0091] A bias voltage V_BIAS+ is supplied to the gate terminal of the first transistor NM_3a which is a fourth node {circle around (4)}, and a bias voltage V_BIAS− is supplied to the gate terminal of the second transistor NM_3b which is a fifth node {circle around (5)}.

[0092] As shown in FIG. 4B, the DC bias voltage V_BIAS is supplied to a sixth node {circle around (6)} in order to bias the first transistor NM_3a and the second transistor NM_3b at an appropriate point to generate a proper gain.

[0093] The third capacitor C₃₂₊ blocks the DC not to be included in the in-phase output signal V_OUT+, and the fourth capacitor C₃₂₋ blocks the DC not to be included in the inverse-phase output signal V_OUT−.

[0094] The fifth capacitor C₃₃ is used for AC-ground for RF signals.

[0095] The DC bias current flows through the first transistor NM_3a and the second transistor NM_3b. Since the bias current flows along the current path 312, the DC current is reused by the first active unit 320 and the second active unit 330.

[0096] FIG. 5 shows a receiver comprising a hybrid balun apparatus in accordance with an embodiment of the present invention.

[0097] As shown in FIG. 5, the receiver 400 according to the present embodiment comprises the hybrid balun apparatus 410, a variable-gain low-noise amplifier 420, a down-conversion mixer 430, a low-pass filter 440, a variable gain amplifier 450 and an oscillator 460.

[0098] Table 2 compares the overall noise factors and gains of a receiver 400 comprising the hybrid balun apparatus 410 shown in FIG. 3 through FIG. 4C and a receiver 400 with a conventional passive balun 100 instead of the hybrid balun apparatus 410.

[0099] As shown in Table 2, the hybrid balun apparatus 410 improves the overall noise factor of the receiver as much as about 1.8 dB and the overall gain of the receiver as much as 3.2 dB.

[0100] Therefore, the improvement of the noise factor significantly improves the receiving sensitivity of the receiver.

[0101]

	TABLE 2
				Overall
			Frequency	performance
		Low-noise	down-	of
	Balun	amplifier	converter	receiver
Passive	Noise factor (dB)	2.75	2	10	6.7
balun	Gain (dB)	−2.75	10	5	12.25
Hybrid	Noise factor (dB)	2.4	2	10	4.88
balun	Gain (dB)	0.45	10	5	15.45

[0102] As described above, the hybrid balun apparatus provides very symmetric differential outputs over a wideband, consumes less DC power, lowers the noise factor, enhances the signal gain, and hardly suffers the linearity problems according to the structure of the present invention.

[0103] Also, the receiving band of the balun apparatus becomes broader compared to the conventional active balun apparatus.

[0104] Furthermore, if the balun apparatus according to the present invention is applied into the receiver, the overall noise factor is lowered, the overall signal gain is improved, the DC power consumption is reduced, and the receiving band becomes wider.

[0105] The foregoing exemplary embodiments and aspects of the invention are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.