Mimo and diversity front-end arrangements for multiband multimode communication engines

[0001] This application is related to U.S. patent application Ser. No. 10/118,657, filed Apr. 8, 2002, and assigned to the assignee of the present application. This application is also related to patent applications Ser. No. 10/688,807 and Ser. No. 10/688,275, assigned to the assignee of the present application and filed even date herewith.

[0002] The present invention relates generally to front-end topology and, more particularly, to front-end arrangement for multiband and/or multimode mobile cellular handset electronics.

[0003] The term “front-end” as used in this disclosure, means the components and functions between the antennas and the power amplifiers or RF-ASIC (radio frequency application specific integrated circuit), but some front-end modules may also include power amplifiers. The front-end in multiband, multimode engines, especially those that are designed to meet the requirement of MIMO (multiple-input, multiple-output) and/or diversity functionality, is usually very complex in construction and design. Because the front-end generally comprises many switches, it consumes a significant amount of electrical current and needs many control lines. MIMO functionality is required in new and future mobile terminals and, initially, Rx MIMO is prioritized because the downlink data rate is more important than the uplink counterpart in mobile communications. Essentially, Rx MIMO requires more than one Rx path to be provided on a particular band of operations. The outputs of these paths are then monitored and combined to give an enhanced data rate. The antenna feed to each of these paths is independent from each other.

[0004] Currently, a GSM/W-CDMA multimode engine is designed to have a separate GSM antenna and a separate W-CDMA antenna. A W-CDMA antenna is connected to a duplexer that has a passband filter for both the Rx and Tx paths of the W-CDMA mode. The GSM antenna is connected to an antenna switch module that typically first separates the 1 GHz frequencies from the 2 GHz bands using a diplexer or the like. The Rx and Tx paths of each frequency range are then separated by switches. The antenna switch module often also includes harmonic filtering for the power amplifier outputs and may include surface-acoustic wave (SAW) filters to provide filtering for the Rx paths. A typical block diagram of a typical front-end is shown in FIGS. 1a and 1b. As shown in FIG. 1a, the GSM module includes four sections: 1 GHz GSM Rx section, 1 GHz GSM Tx section, 2 GHz GSM Rx section and 2 GHz GSM Tx section. The 1 GHz GSM Rx section includes an 869–894 MHz Rx path 110, and the 925–960 MHz Rx path 130. The 1 GHz GSM Tx section, collectively denoted as path 150, includes two frequency bands of 824–849 MHz and 880–905 MHz. The 869–894 MHz Rx path 110 includes a filter 116 connected between ports 112 and a balun 122. The 925–960 MHz Rx path 130 includes a filter 136 connected between ports 132 and a balun 142. The balun functionality can be incorporated into the filters 116 & 136 depending on the filter technology. The Rx paths 110 and 130 are joined at a common node 410. These Rx paths are also joined with the port 152 of the 824–849/880–905 MHz Tx path 150 at a node 412 via a matching element 80. Here PIN diodes 42 and 44 are used for Tx-Rx switching. Alternatively, other switch technologies can be also used e.g. CMOS or GaAs p-HEMTs (Pseudomorphic High Electron Mobility Transistor). However, by using the CMOS and p-HEMT switches, the arrangement of biasing and matching elements will be slightly modified.

[0005] The 2 GHZ Rx section includes a 1805–1880 MHz Rx path 220, commonly referred to as the 1800GSM mode, and the 1930–1990 MHz Rx path 240, commonly referred to as the 1900GSM mode. The 2 GHz GSM Tx section, collectively denoted as path 260, includes two frequency bands of 1710–1758 MHz and 1850–1910 MHz. The 1805–1880 MHz Rx path 220 includes a filter 226 connected between ports 222 and a balun 232. The 1930–1990 MHz Rx path 240 includes a filter 246 connected between ports 242 and a balun 252. The Rx paths 220 and 240 are joined at a common node 414 with matching circuits or devices 84, 86. These Rx paths are also joined with the port 262 of the 1710–1758/1850–1910 MHz Tx path 260 at a node 416 via a matching element 82. Here PIN diodes 46, 48 are used for Tx-Rx switching. The 1 GHz and 2 GHZ parts are connected to a common feed point 418 of the GSM antenna 10 through a diplexer 30, which comprises harmonic filters 32, 34 for the Tx paths 150 and 260.

[0006] In FIG. 1b, the W-CDMA module has two paths: a 2110–2170 MHz Rx path 320 and a 1920–1980 MHz Tx path 340. The Rx path 320 includes a filter 326 connected between ports 322 and a balun 332. However, the balun can also be after the filter and external to the duplexer. The 1920–1980 Tx path 340 has a passband filter 346 and a port 342. The Rx path 320 is joined with the Tx path 340 at a node 420 and a common W-CDMA antenna 20 via a matching element 90.

[0007] To use one antenna for the GSM mode and one antenna for the W-CDMA mode, it is required that the front-end includes matching devices 80, 82, 84, 86 and other necessary components for matching and biasing, depending also on the switch technology chosen, to separate the 1805–1880 MHz GSM Rx path 220 and the 1930–1990 MHz GSM Rx path 240. The front-end architecture is complex and the additional losses in these reception paths occur.

[0008] It is advantageous and desirable to provide a front-end architecture where the complexity can be reduced.

[0009] The present invention reduces the complexity of frond-end design by combining one or more 2 GHz GSM Rx paths with one or more W-CDMA Rx paths. With such a combination, the number of matching elements and the switching components can be reduced or even eliminated. As a result, the current consumption and the losses in the front-end engines can also be reduced. Preferably, the front-end engine comprises one or more receive front-end modules, each module having at least two feed points operatively connected to at least two antennas for receiving communication signals. The modules can be the same or different.

[0010] Thus, according to the present invention, there is provided a receive front-end module for use in a multi-band, multi-mode communication device, the communication device having a plurality of electrically separated antennas. The receive front-end module comprises:

[0011] at least two feed points, separately connected to at least two of said plurality of antennas for receiving communication signals in the communication device;

[0012] a plurality of signal paths, operatively connected to the feed points for simultaneously receiving communication signals in a plurality of frequency bands, wherein each signal path has a filter for filtering the communication signals in the corresponding frequency band; and

[0013] at least one isolation component, disposed in the signal paths, for providing cross-band isolation between at least two of the signal paths.

[0014] The isolation component comprises at least one signal amplifier.

[0015] The two antennas comprise a first antenna and a second antenna, and the two feed points comprises a first feed point operatively connected to the first antenna, and a second feed point operatively connected to the second antenna, and wherein said plurality of signal paths comprises:

[0016] a first signal path having a first filter for filtering the communication signals in the first frequency band, the first signal path operatively connected to the first feed point;

[0017] a second signal path having a second filter for filtering the communication signals in the second frequency band, the second signal path operatively connected to the second feed point;

[0018] a third signal path having a third filter for filtering the communication signals in the third frequency band, the third signal path operatively connected to the second feed point, wherein the third frequency band is different from the second frequency band; and

[0019] means, for matching the second and third filters.

[0020] Advantageously, the receive front-end module further comprises:

[0021] a first balun disposed in the first signal path between the first filter and the first feed point;

[0022] a second balun disposed in the second signal path between the second filter and the second feed point; and

[0023] a third balun disposed in the third signal path between the third filter and the second feed point.

[0024] The isolation component comprises:

[0025] a first signal amplifier disposed in the first signal path, operatively connected to the first filter;

[0026] a second signal amplifier disposed in the second signal path, operatively connected to the second filter; and

[0027] a third signal amplifier disposed in the third signal path, operatively connected to the third filter.

[0028] The first frequency band substantially covers a frequency range of 1805–1880 MHz, the second frequency band substantially covers a frequency range of 1930–1930 MHz, and the third frequency band substantially covers a frequency range between 2110 MHz and 2170 MHz.

[0029] The communication signal received in the first signal path is transmitted in a GSM mode;

[0030] the communication signal received in the second signal path is transmitted either in a GSM mode or a W-CDMA mode; and

[0031] the communication signal received in the third signal path is transmitted in a CDMA mode.

[0032] Alternatively, the first and second frequency bands substantially cover a frequency range between 2110 MHz and 2170 MHz, and the third frequency band substantially covers a frequency range between 1805 MHz and 1880 MHz; and

[0033] The communication signal received in the third signal path is transmitted in a GSM mode; and the communication signals received in the first and the second signal paths are transmitted in a W-CDMA mode.

[0034] Advantageously, the receive front-end module further comprises:

[0035] a first balun disposed in the first signal path between the first filter and the first feed point;

[0036] a second balun disposed in the second signal path between the second filter and the second feed point; and

[0037] a third balun disposed in the third signal path between the third filter and the second feed point.

[0038] The isolation component comprises:

[0039] a first signal amplifier disposed in the first signal path, operatively connected to the first filter;

[0040] a second signal amplifier disposed in the second signal path, operatively connected to the second filter; and

[0041] a third signal amplifier disposed in the third signal path, operatively connected to the third filter.

[0042] Alternatively, the two antennas comprise a first antenna and a second antenna, and said at least two feed points comprise a first feed point operatively connected to the first antenna, and a second feed point operatively connected to the second antenna, and wherein said plurality of signal paths comprises:

[0043] a first signal path having a first filter for filtering the communication signals in the first frequency band, the first signal path operatively connected to the first feed point, and

[0044] a second signal path having a second filter for filtering the communication signals in the second frequency band, the second signal path operatively connected to the second feed point, and wherein said plurality of antennas further comprising a third antenna electrically separated from the first and second antenna. The module further comprises:

[0045] a third feed point, operatively connected to the third antenna for receiving communication signals in the communication device;

[0046] a third signal path, operatively connected to the third feed points for receiving communication signals in a third frequency bands; and

[0047] further means, disposed in the third signal path, for providing cross-band isolation between the third signal path and at least one of said at least two signal paths.

[0048] The communication signal received in the first and second signal paths is transmitted in a frequency band substantially between 2110 MHz and 2170 MHz, and the communication signal received in the third signal path is transmitted in a frequency band substantially between 1930 MHz and 1990 MHz.

[0049] Advantageously, the receive front-end module further comprises:

[0050] a first balun disposed in the first signal path between the first filter and the first feed point;

[0051] a second balun disposed in the second signal path between the second filter and the second feed point; and

[0052] a third balun disposed in the third signal path between the third filter and the second feed point.

[0053] Advantageously, the isolation component comprises:

[0054] a first signal amplifier disposed in the first signal path, operatively connected to the first filter; and

[0055] a second signal amplifier disposed in the second signal path, operatively connected to the second filter, and wherein said further isolation means comprises

[0056] a third signal amplifier disposed in the third signal path, operatively connected to the third filter.

[0057] Advantageously, the receive front-end module further comprises a fourth signal path operatively connected to a different one of said plurality of antennas for receiving communication signals in a frequency band substantially between 1930 MHz and 1990 MHz.

[0058] The received communication signals in first and second signal paths are transmitted in one of the following modes: W-CDMA (EU) and W-CDMA (US2). The received communication signals in the third and fourth signal paths are transmitted in one of the following modes: W-CDMA (US1) and 1900GSM.

[0059] The received communication signals in the third signal path are transmitted in W-CDMA (US1) mode, and the received communication signals in the fourth signal path are transmitted in one of the following modes: W-CDMA (US1) and 1900GSM.

[0060] Advantageously, the baluns are integrated in a sub-module, and the signal amplifiers are integrated in a sub-module.

[0061] Preferably, the receive front-end module comprises:

[0062] a first sub-module for disposing the first, second and third feed points and the first, second and third signal paths; and

[0063] a second sub-module for disposing the fourth signal path.

[0064] Advantageously, the receive front-end module further comprises:

[0065] a further antenna having a further feed point;

[0066] a fourth signal path, operatively connected to the further feed point, for receiving a communication signal in a fourth frequency band;

[0067] a fifth signal path, operatively connected to the further feed point, for receiving a communication signal in a fifth frequency band different from the fourth frequency band, wherein each of the fourth and fifth signal paths has

• • [0068] an input end and an output end, the input end operatively connected to the further feed point,
  • [0069] a balun disposed at the input end,
  • [0070] a signal amplifier disposed at the output end, and
  • [0071] a filter disposed between the signal amplifier and the balun; and

[0072] means, operatively connected to the further feed point, for matching the filters in the fourth and fifth signal paths.

[0073] The communication signals received in the first and second signal paths are transmitted in a frequency band substantially between 2110 MHz and 2170 MHz in a W-CDMA mode, and the communication signals received in the third and fourth signal paths are transmitted in a frequency band substantially between 1930 MHz and 1990 MHz in either a W-CDMA mode or a GSM mode.

[0074] The communication signals received in the fifth signal path are transmitted in the fifth frequency band substantially between 1805 MHz and 1880 MHz.

[0075] Alternatively, the receive front-end comprises:

[0076] a first sub-module for disposing the first, second and third signal paths and the first, second and third feed points, and

[0077] a second sub-module for disposing the fourth and fifth signal paths and the further feed point.

[0078] The receive front-end module further comprises a sixth signal path, operatively connected to the further feed point, for receiving a communication signal in a sixth frequency band different from the fourth and the fifth frequency band, the sixth signal path having

[0079] an input end and an output end, the input end operatively connected to the further feed point,

[0080] a balun disposed at the input end,

[0081] a signal amplifier disposed at the output end,

[0082] a filter disposed between the signal amplifier and the balun for filtering the communication signal in the sixth frequency band, wherein

[0083] the matching means is also used for matching the filter in the sixth signal path.

[0084] The communication signals received in the first, second and sixth signal paths are transmitted in a frequency band substantially between 2110 MHz and 2170 MHz in a W-CDMA mode,

[0085] the communication signals received in the third and fourth signal paths are transmitted in a frequency band substantially between 1930 MHz and 1990 MHz in either a W-CDMA mode or a GSM mode, and

[0086] the communication signals received in the fifth signal path are transmitted in the fifth frequency band substantially between 1805 MHz and 1880 MHz.

[0087] Alternatively, the two antennas comprise a first antenna and a second antenna, and the two feed points comprise:

[0088] a first feed point, operatively connecting a first signal path to the first antenna, for receiving communication signals in a first frequency band, and

[0089] a second feed point, operatively connecting a second signal path to the second antenna, for receiving communication signals in the second frequency band, and said plurality of antenna further comprising a fourth antenna, a fifth antenna, and a sixth antenna, and the receive front-end module further comprises:

[0090] a fourth feed point, operatively connecting a fourth signal path to the fourth antenna, for receiving communication signals in the fourth frequency band;

[0091] a fifth feed point, operatively connecting a fifth signal path to the fifth antenna, for receiving communication signals in the fifth frequency band; and

[0092] a sixth feed point, operatively connecting a sixth signal path to the sixth antenna, for receiving communication signals in the sixth frequency band, and wherein the receive front-end module comprises a first sub-module for disposing the first, second and third signal paths, and a second sub-module for disposing the fourth, fifth and sixth signal paths, and the

communication signals in at least two of the six signal paths are transmitted in the same frequency band and transmission mode.

[0093] Advantageously, the first and fourth signal paths in which the received communication signals are transmitted substantially in a frequency range between 2110 MHz and 2170 MHz;

[0094] the second and third signal paths in which the received communication signals are transmitted substantially in a frequency range between 1930 MHz and 1990 MHz; and

[0095] the fifth and sixth signal paths in which the received communication signals are transmitted substantially in a frequency range between 1805 and 1880 MHz.

[0096] According to the second aspect of the present invention, there is provided a method of enhancing reception of communication signals in a multi-band, multi-mode communication device, the communication device having a plurality of electrically separated antennas, and a plurality of signal paths for receiving communication signals in a plurality of frequency bands. The method comprises the steps of:

[0097] providing at least a first feed point and a second feed point separately connected to at least two of said plurality of antennas;

[0098] operatively connecting at least one of said plurality of signal paths to the first feed point, and at least a different one of said plurality of signal paths to the second feed point, each of the signal paths connected to the first and second feed points has a filter for filtering the communication signals in the corresponding frequency band; and

[0099] providing means, in at least some of the signal paths, for providing cross-band isolation between at least two of said plurality of signal paths, wherein

[0100] the communication signals received in at least one of the signal path connected to the first feed point and the communication signals received in at least one the signal path connected to the second feed point are transmitted in the same frequency band and transmission mode.

[0101] According to the third aspect of the present invention, there is provided a multi-band, multi-mode communication device, comprising:

[0102] a plurality of electrically separated RF antennas, including a first antenna and a second antenna, and

[0103] a front-end module comprising:

• • [0104] at least a first feed point and a second feed point separately connected to the first and second antennas, and
  • [0105] a plurality of signal paths operatively connected to the first and second feed points for receiving communication signals in a plurality of frequency bands, each signal path having a filter for filtering the communication signals in the corresponding frequency band, wherein

[0106] the communication signals received in at least one of the signal path connected to the first feed point and the communication signals received in at least one the signal path connected to the second feed point are transmitted in the same frequency band and transmission mode.

[0107] The portable communication device can be a mobile terminal, a communicator device or the like.

[0108] The present invention will become apparent upon reading the description taken in conjunction with FIGS. 2a to 10.

[0131] The upper (2 GHz) GSM band Rx and Tx performance in a multiband, multimode mobile terminal (or a communicator device and the like) can be improved by relocating some of the GSM and W-CDMA paths in the front-end of the engine. The mobile terminal 1 is schematically shown in FIG. 10, which shows a transceiver front-end 2 comprising a first module 4 operatively connected to an antenna 10, and a second module 8 operatively connected to one or more antennas 20.

[0132] According to one embodiment of the present invention, the 1800GSM Rx (1805–1880 MHz) is moved from the antenna switch to the W-CDMA duplexer. As shown in FIG. 2a, the 2 GHz part of the GSM module has only one Rx path 240: 1900GSM Rx (1930–1990 MHz). As such, the matching elements 84 and 86 (see FIG. 1a) can be eliminated. The 1800GSM Rx path 220 shares the upper band antenna 20 of the W-CDMA module, as shown in FIG. 2b. Because of the different operation modes between the W-CDMA duplexer (Rx path 320 and Tx path 340) and the GSM, the 1800GSM Rx path 220 can be directly connected to the node 422, without the need of switches. Only one matching element 92 is used to match one of the filters. This arrangement reduces the losses of this specific Rx band up to 2 dB due by avoiding the losses caused by the switches for Tx-Rx switching and the diplexer 30 or the like (see FIG. 1a). It should be noted that the switching as shown in FIG. 2a is accomplished by PIN diodes in a series (48)/shunt (46) configuration, requiring a λ/4 transmission line or a 90 degree phase shifter (82). However, there are also other alternatives: both of the diodes could be in series, and the diodes can also be replaced by CMOS switches, p-HEMT switches or the like.

[0133] A further improvement for reducing the losses of the 1900GSM Rx and the 1800 & 1900GSM Tx can be realized by using separate passband filters in the (1710–1758)/(1850–1910) GSM Tx path 260. As shown in FIG. 3, a separate matching circuit 270 and a separate passband filter 266 are used for the 1800GSM Tx (1710–1785 MHz), and a separate matching circuit 272 and a passband filter 268 are used for the 1900GSM Tx (1850–1910 MHz). As such, the switching elements 46, 48 and 82 (see FIG. 2a) and the harmonic filter 34 are eliminated and replaced by selective Tx passband filters 266, 268. These two passband filters are matched at both ends with circuits 270, 272, which are passive elements that can be integrated into the module, for example. The removal of the switches and the diplexer/harmonic filter renders it possible to match all three filters to one single antenna feed point 510 without switching. In this arrangement, the 1900GSM Rx filter 246 and the corresponding 1900GSM Tx filter 268 act like a duplexer. Thus, insertion loss can be reduced.

[0134] Moreover, the 1920–1980 MHz W-CDMA path 340 in the FIG. 2b and the 1900GSM Rx path 240 in FIG. 3 can change places, as shown FIGS. 4a and 4b. As shown in FIG. 4a, the 1920–1980 MHz W-CDMA Tx path 340 is directly connected to the antenna feed point 510 without the need of the matching element 92 (see FIG. 2b). As shown in FIG. 4b, although there are three Rx paths 220, 240, 320 connected to the antenna 20 with one antenna feed point 520, only one matching circuit 274 is needed for matching one of the filters. Such arrangement provides additional benefits.

[0135] In the arrangement as shown in FIGS. 4a and 4b, all the upper band Rx and Tx paths are separated. The upper band Rx paths are connected to the antenna 20, while the upper band Tx paths are connected to the antenna 10. As such, the Rx and Tx antennas 10, 20 can be unbalanced antennas, with each antenna in a separate module. Furthermore, each module has three filters for the upper band that are matched to one single feed point with one matching element. As with the switching elements 48, 46, 82 in FIG. 2a, the matching elements in FIG. 4a can be replaced by CMOS or p-HEMT switches.

[0136] The separate antennas for the Rx and Tx paths provide some “for free” Tx to Rx attenuation. The term “for free” in this context means that, in order to have more than one antenna that are not too much influenced by each other (loading conditions at antenna port etc), there must be a certain amount of isolation between the antennas, typically 10 dB being a minimum requirement. This is the case even in the conventional GSM vs W-CDMA antenna arrangement. This means that, with a proper Rx and Tx arrangement, the 10 to 20 dB of isolation can be used to attain some of the required Tx to Rx isolation as well. This results in some relaxation in the duplexing requirements. Furthermore, the Rx antenna 20 can now be optimized for omni-directionality. Likewise, the upper band Tx antenna 10 can be optimized to achieve as low SAR (specific absorption rate) as possible for low radiation mobile phones. Moreover, because the impedance level of the Rx chain is typically higher than that of the Tx counterpart, the antenna impedance can be designed to suit the upper band Rx and upper band Tx only, when the Rx and Tx chains are connected to different antennas.

[0137] The methods as discussed above can be used in a front-end engine for U.S. current or future W-CDMA frequencies, or in a front-end engine having mixed use of European and U.S. W-CDMA frequencies. More particularly, the present invention is applicable to any given set of at least three frequency bands that are close, but not overlapping in frequency. For example, the 2 GHz GSM Tx path 260 as shown in FIG. 4a can also be used for the current U.S. W-CDMA (US1, Tx 1850–1910 MHz) and the new U.S. W-CDMA (US2, Tx 1710–1755 MHz). These modes share the same antenna 10 with the EU W-CDMA Tx path 340. Likewise, the 1900GSM Rx path 240 as shown in FIG. 4b can also used for the current U.S. W-CDMA (US1, Rx 1930–1990 MHz), and the European W-CDMA Rx path 320 can also be used for the new U.S. W-CDMA (US2, Rx 2110–2155 MHz). It should be noted that the W-CDMA US2 Rx has a smaller bandwidth than the European counterpart (2110–2170 MHz). Furthermore, not all of the GSM and W-CDMA bands have to be implemented on a Tx/Rx system. In order to accommodate different W-CDMA standards, the relevant filters must be designed to have different passband frequencies.

[0138] FIGS. 5a and 5b shows different embodiments of the 2 GHz Rx module as shown in FIG. 4b. The filters 226, 246 and 326 in these different embodiments are either fully balanced and each is associated with a balun in front thereof, or each of filters has a single to balanced function included therein (acoustic balun). As shown in FIG. 5a, the balun and the filter in each path are integrated into a filter that includes the single to balanced transformation. The filters that have the single to balanced transformation in the Rx paths 220, 240 and 320 are denoted by reference numerals 228, 248 and 328, respectively.

[0139] When separate baluns 232, 252, 332 are used, as shown in FIG. 4b, each of them covers the frequency range of the corresponding filter (226, 246, 326). Alternatively, one balun 334 is used for all three paths 220, 240 and 320, as shown in FIG. 5b. In this case, the balun 334 covers the entire frequency ranges of the three filters 226, 246 and 326, and one matching element 276 is used to match one of the filters. The filters can be either SAW (surface acoustic wave) filters or BAW (bulk acoustic wave) filters. With three filters in one Rx module, as shown in FIGS. 4b and 5a, only the filter with the frequency that lies between the lowest and the highest frequency bands needs a matching element, which can be typically implemented with one capacitor and one or more inductors. The matching can also be carried out using striplines or different arrangements of coils and capacitors. The matching of at least three filters to a single point is generally possible if the frequency separation among these filters is not too small (the matching with a frequency separation of 1GHz or 2 GHz is straightforward). The limit of the frequency separation depends on the filter technology and selectivity requirements, but a typical minimum is around 1% of the center frequency (i.e. filters close to 2 GHz, for example the GSM 1800 and 1900, W-CDMA 2110. Rx filters, are possible to match since the separation between the upper passband edge of 1800 and the lower edge of 1900 have a separation of 20 MHz and a larger separation to the W-CDMA Rx). In the above example, the three different frequency ranges are 1805–1880 MHz, 1930–1990 MHz and 2110–2170 MHz.

[0140] The separation of Rx and Tx antennas in the upper bands together with the steep Rx filters provides sufficient Tx to Rx isolation to render any additional Tx/Rx switching unnecessary. Furthermore, it is possible to design the filters so that they are selective enough to achieve Tx to Rx isolation. However, the problem of cross band isolation remains to be solved. This problem arises from the fact that even though the Tx and Rx bands of a given standard do not overlap, there may be, in a multiband engine, overlapping between Tx frequencies of one standard and Rx frequencies of another standard. For example the 1900GSM standard has its Tx mode at 1850–1910 MHz and the corresponding Rx mode at 1930–1990 MHz (thereby having a separation of 20 MHz). The Tx mode does partially overlap with the 1800GSM Rx, which is operated at 1805–1880 MHz. This means that even when the signal from the Tx antenna is correctly attenuated in the 1900GSM Rx filter, the signal is able to pass trough the 1800GMS Rx filter. From the system point of view this is problematic because the next element in the Rx chain is usually an LNA (low noise amplifier), which is already integrated on to an RF-ASIC. Even though the LNA for the 1800GSM would be in the OFF state, sufficiently high signal levels may exist at the input to the RF-ASIC die, e.g. the bondwires, causing interference in the operation of the RF-ASIC. This is especially true for modem RF-ASIC that operates on very low supply voltages like 1.2V. In such a case, a high level input signal may even damage the RF-ASIC itself. Moreover, the only attenuation in these cross band situations is provided by the separate antennas and is about 10–15 dB. This attenuation is not enough. These potential cross band frequencies are shown in FIGS. 6a and 6b for the case involving 1800GSM, 1900GSM and the European W-CDMA.

[0141] As shown in FIG. 6a, the upper band Tx chain connected to the antenna 10 includes 1800GSM Tx_—3 (1710–1785 MHz): 1900GSM Tx_—4 (1850–1901 MHz) and W-CDMA (EU) Tx_—7 (1920–1980 MHz), and the upper band Rx chain connected to the antenna 20 includes 1800GSM Rx_—3 (1805–1880 MHz), 1900GSM Rx_—4 (1930–1990 MHz) and W-CDMA (EU) Rx_—7 (2110–2170 MHz). Thus, the frequency overlap in these chains is: Tx_—4-Rx_—3 (30 MHz, from 1850 to 1880 MHz), and Tx_—7-Rx_—4 (50 MHz, from 1930 to 1980 MHz). The cross band problems are also illustrated in FIG. 6b. If the maximum output power at the antenna in Tx mode is 30 to 33 dBm (depending on system standard) and a typical isolation that can be achieved between two separate antennas is between 10 to 20 dBm, for example, then the power level at the Rx antenna is from 13 to 23 dBm. In such a case, the antennas do provide some free Tx to Rx isolation, but for the crossband this is not sufficient, since a typically acceptable maximum power level at the Rf-ASIC input (Rx path) is around 0 dBm during Tx time slot (i.e. LNAs in ASIC are off). Therefore, some means of providing additional attenuation in these cross band cases is needed.

[0142] Sufficient cross band isolation can be achieved in a multiband engine by basically two methods: either implementing switching in the Rx paths that are problematic, or moving some or all of the LNAs from the ASIC to the Rx module. The switches provide adequate increase in isolation, but also increase the insertion loss (the switches can have different arrangement, e.g. in shunt to ground). Cross-band isolation in the 2 GHz Rx module using switches is shown in FIG. 7a. For example, a PIN diode 50 is used as a switch in the 1800GSM Rx path 220 such that the PIN diode 50 is switched off when the 1900GSM Tx mode is used in order to provide good isolation to the 1800GSM Rx path 220. Likewise, a PIN diode 52 is used as a switch in the 1900GSM Rx path 240 such that the PIN diode 52 is switched off when the European W-CDMA Tx mode is used in order to provide good isolation to the 1900GSM Rx path 240. As shown in FIG. 7a, the passive elements including the baluns 232, 252, 332, the matching element 274 and the switches 50, 52 can be integrated into a sub-module 610. The filters 226, 246 and 326 are separately fabricated as discrete sub-modules 620, 622 and 624. All these sub-modules can be assembled into an Rx module 600.

[0143] The LNAs method can, in principle, provide this isolation as a bonus, since an unbiased (=OFF) LNA has very good isolation (from input to output) and hence the signal level at the output of a LNA in the OFF state is small enough for the RF-ASIC. Moving the LNAs out from the RF-ASIC to the filter module also has several other benefits that are discussed later.

[0144] Cross-band isolation using LNAs is shown in FIG. 7b. As shown, three low noise amplifiers 224, 244 and 324 are used, respectively, in the 1800GSM Rx path 220, 1900GSM Rx path 240 and W-CDMA Rx path 320. The low noise amplifiers 224, 244 and 324 are integrated in a sub-module 630. The passive elements including the baluns 232, 252, 332 and the matching element 274 are integrated into a sub-module 612. The filters 226, 246 and 326 are separately fabricated as discrete sub-modules 620, 622 and 624. All these sub-modules can be assembled into an Rx module 601. When operating at 1900GSM Rx mode, only the LNA 244 is ON, and the 1800GSM LNA 224 is OFF in order to provide necessary isolation. Similarly, when operating at W-CDMA (EU or US2) with the Rx path 320, only the LNA 324 is ON. The 1900GSM LNA 244 is OFF. The advantages of such an arrangement include that the LNA at the OFF-state provides isolation “for free” and it works as a switch, and that the matching between the filters and the LNAs can be designed to achieve optimal performances. It should be noted that only the bipolar process is required for the low noise amplifiers. An RF-ASIC can be made of CMOS.

[0145] If the baluns in the Rx modules are not acoustic baluns, as those shown in FIGS. 5a, 7a and 7b, they can be integrated with passive matching elements on e.g. very small silicon chips. It should be noted that the 1900GSM Rx path 240 is also used for the current U.S. W-CDMA (US1) Rx mode, and the European W-CDMA Rx path 320 is also used for the new U.S. W-CDMA (US2) Rx mode, as shown in FIG. 7c. The receive module as shown in FIG. 7c is a single-antenna module in a “WORLD” EU/US2/US1 and 1800/1900GSM Rx combination. However, it is preferred that two antennas are disposed on an Rx module 602, as shown in FIG. 8a.

[0146] An additional benefit of separating the upper band RX and Tx is that the front-end architecture is well suited to support Rx-MIMO/diversity functionality.

[0147] In a MIMO receive module, at least two of the signal paths connected to two different antennas are used simultaneously to receive signals of the same mode in the same frequency band. For example, in the W-CDMA EU/US2 MIMO and 1800GSM Rx combination shown in FIG. 8b, the W-CDMA EU/US2 paths 320 are separately connected to two antennas 22 and 24. The second antenna 24 is also matched to the 1800GSM Rx path 220.

[0148] It is also possible to connect the receive signal paths to three separate antennas in an Rx module, as shown in FIG. 8c. As shown in the figure, the Rx module 603 has two identical signal paths 320, separately connected to two antennas 22 to achieve W-CDMA EU/US2 MIMO requirement. The third signal path 240 is used for the W-CDMA US1 and 1900GSM Rx combination. It should be noted that, in the Rx module 603, it is not necessary to include the LNAs 324 and 244. The module can also have switches to take care of the cross-band isolation problem.

[0149] In diversity, the only requirement is the duplicating of the module. For example, two identical Rx modules (601 in FIG. 7b or 601′ in FIG. 7c, for example) can be used side-by-side, as shown in FIG. 8d. In such case, only one Tx module (FIG. 4a, for example) is necessary.

[0150] The Rx modules, as shown in FIGS. 7b, 7c, 8a, 8b and 8c, can be combined or used together to achieve further MIMO and Diversity variant requirements. For example, the MIMO Rx modules 603, as shown in FIG. 8c, and the Rx module 601, as shown in FIG. 7c, can be used together to achieve Rx antenna diversity. As shown in FIG. 8e, the Rx modules 603 and 601 are used together to provide three W-CDMA (EU/US2) Rx paths 320 (via Antenna 1, Antenna 3 and Antenna 4), two W-CDMA (US1/1900GSM) Rx paths 240 (via Antenna 2 and Antenna 4) and one 1800GSM Rx path 220 (via Antenna 4). In this arrangement, both the 240 paths can be used for 1900GSM Rx diversity. Alternatively, one of the 240 paths is normally used for W-CDMA US1 Rx, but can also be used for monitoring 1900GSM Rx signals. Optionally, one of the W-CDMA Rx paths 320 can be omitted so that only two W-CDMA (EU/IUS2) paths 320 are made available. The Rx modules 601 and 603 can be combined into one module, or they are used as two modules.

[0151] With the upper band Rx paths being separated from the upper band Tx paths, the Rx module with three antennas can be used to achieve GSM Rx antenna diversity. As shown in FIG. 9a, one antenna is linked to a single W-CDMA (EU/US2) Rx path 320. Two antennas are separately linked to two 1800GSM Rx paths 220 to achieve 1800GSM diversity. Similarly, two antennas can be separately linked to two 1900GSM Rx paths 240 to achieve 1900GSM diversity, as shown in FIG. 9b.

[0152] In the modules that contain upper band Tx paths, such as 1800 & 1900GSM Tx paths 260 and/or W-CDMA (EU) Tx path 340, the 1800GSM Tx band and the 1900GSM Tx band, in most cases, are provided from one common power amplifier (PA). Thus, the Tx filtering of the upper band GSM Tx path can be done with one harmonic filter, such as filter 34 in FIG. 2a, that has a wide enough passband to cover both GSM Tx bands. Alternatively, Tx filtering is achieved by using two passband filters, such as filters 266, 268 in FIGS. 3 and 4a, that are matched to each other at both the output end and the input end. The W-CDMA Tx path 340 requires a separate filter, such as passband filter 346 in FIG. 4a. Any of the harmonic filter 34, passband filters 266, 268 and 346 can be a balanced filter, or a filter that performs a single to balance transformation, depending on whether any of the power amplifiers has a differential output.

[0153] The 1 GHz GSM bands 110, 130, 150 are either connected to the Tx or the Rx antenna using a conventional antenna switch approach. That is, one of the antennas has to be designed such that it also has a resonance at 1 GHz. The main reason for this is that the 1 GHz antenna is the largest one and it is seen, therefore, as not feasible to have separate Tx and Rx antennas for the lower bands.

[0154] The advantages of this invention are many (some may depend on the specific band combination and implementation):

• • [0155] The reduction of number of switches: lower insertion loss, less control lines, smaller current consumption (one PIN diode draws from 4 to 10 mA of current). Switch associated bias components reduction
  • [0156] Separate Rx and Tx antennas: for free Tx to Rx isolation, less stringent filtering requirements (especially in CDMA applications), smaller number of components.
  • [0157] LNAs in the Rx module (or on the module, where the Rx filters are): OFF-state LNA provides for free cross band isolation (no need for switches), matching between the filters and LNA can be designed ideally with no unknown factors from various engine board designs (routing etc), only bi-polar needed, system level noise figure in most cases improved and has less variation, in MIMO applications the whole Rx module can be duplicated and due to LNAs in the module even longer connections to RF-ASIC cause only small variations in noise figure and gain (equal noise figure in the different Rx-branches is important in a MIMO receiver).
  • [0158] Modules having common footprint, I/O allocation may be used with only the internal die selected, depending on the build required.
  • [0159] The filtering of GSM Tx with truly selective filters obviate the need for switches, since at least three filters with no over lap in frequency can be matched to one single feed point.
  • [0160] The Rx antenna 20 can be optimized for omni-directionality, whilst the upper band Tx antenna 10 can be optimized to achieve as low SAR (specific absorption rate) as possible for low radiation from the mobile terminal.

[0161] Although the invention has been described with respect to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention.