Abstract:
A receive front-end module in a multi-band communication device. The communication device comprises a plurality of signal paths for receiving and transmitting communication signals in a plurality of frequency bands in GSM and W-CDMA modes. The signal paths in the receive front-end module are operatively connected to a common feed point, which is connected to one of the RF antennas of the communication device, and the signal paths are selected such that none of the frequency bands for receiving communication signals in the receive front-end module are overlapping. If the communication device also transmits the communication signal in at least one transmit frequency range partially overlapping with one of the frequency bands in the receive front-end module, switching means is provided to at least one of signal paths in the receive front-end module for providing cross-band isolation between the transmitted and received communication signals.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [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 Docket No. 944-005-016 and Docket No. 944-005-023, assigned to the assignee of the present application and filed even date herewith. 
     
    
     FIELD OF THE INVENTION  
       [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.  
       BACKGROUND OF THE INVENTION  
       [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. 1   a  and  1   b . As shown in  FIG. 1   a , 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  &amp;  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. 1   b , 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.  
       SUMMARY OF THE INVENTION  
       [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 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.  
         [0010]     Thus, according to the first aspect of the present invention, there is provided a receive front-end module for use in conjunction with a transceive front-end module in a multi-band communication device, the communication device having at least a first antenna and a second antenna electrically separated from the first antenna, wherein the transceive front-end module comprises a plurality of signal paths operatively connected to the first antenna for transmitting signals in at least a first transmit frequency band and a different second transmit frequency band. The receive front-end module comprises: 
        a feed point, operatively connected to the second antenna for receiving communication signals in the communication device; and     a plurality of receive signal paths, operatively connected to the feed point for receiving communication signals in a plurality of frequency bands, wherein said plurality of frequency bands includes at least     a first receive frequency band, which is partially overlapped with the first transmit frequency band in the transceive front-end module, and     a second receive frequency band, which is spaced from the first receive frequency band in frequency.        
 
         [0015]     The first transmit frequency band comprises a frequency range substantially from 1850 MHz to 1910 MHz, and the first receive frequency band comprises a frequency range substantially from 1805 MHz to 1880 MHz.  
         [0016]     Alternatively, the first transmit frequency band comprises a frequency range substantially from 1920 MHz to 1980 MHz, and the first receive frequency band comprises a frequency range substantially from 1930 MHz to 1990 MHz.  
         [0017]     The second receive frequency band is partially overlapped with the second transmit frequency band, and the second transmit frequency band comprises a frequency range substantially from 1850 MHz to 1910 MHz, and the second receive frequency band comprises a frequency range substantially from 1805 MHz to 1880 MHz.  
         [0018]     Alternatively, the second receive frequency band comprises a frequency range substantially from 2110 MHz to 2170 MHz. But this frequency band can also be a third frequency band.  
         [0019]     Preferably, the receive front-end module of claim  7 , wherein further comprising at least one matching circuit, operatively connected to the plurality of receive signal paths, for impedance matching.  
         [0020]     The matching circuit comprises at least one capacitive element, one inductive element or distributed element.  
         [0021]     Advantageously, the receive front-end module further comprises a plurality of filters disposed in the plurality of signal paths for filtering signals in corresponding frequency ranges. The filters can be surface acoustic wave filters, or bulk bulk acoustic wave filters.  
         [0022]     Advantageously, the receive front-end module further comprises: 
        a plurality of baluns, each balun disposed between the feed point and one of the filters. The baluns can be acoustic baluns, or they are integrated with the filters.        
 
         [0024]     The filters can also have a single-to-balanced function included therein.  
         [0025]     Advantageously, the receive front-end module further comprises: 
    at least one isolation component, operative connected to at least one of the receive signal paths, for providing cross-band isolation between the transmitted signals and the received signals. The isolation component comprises: 
        at least one switching element, such as a pin diode or a solid switching device, operatively disposed between the feed point and said at least one of the receive signal paths, for carrying out said isolation.    
       
 
         [0028]     Alternatively, the isolation component comprises: 
        a plurality of signal amplifiers disposed in the receive signal paths for isolating the communication signals.        
 
         [0030]     Advantageously, the receive front-end module further comprises at least one matching circuit, operatively connected to the feed point, for matching the filters.  
         [0031]     According to the second aspect of the present invention, there is provided a method of reducing reception loss in a portable communication device, the communication device having 
        a first antenna;     a second antenna electrically separated from the first antenna;     a plurality of transmit signal paths for transmitting communication signals in at least a first transmit frequency band and a different second transmit frequency band;     a plurality of receive signal paths for receiving communication signals in a plurality of frequency bands, including at least     a first receive frequency band, which is partially overlapped with the first transmit frequency band, and     a second receive frequency band spaced from the first receive frequency band in frequency. The method comprises the steps of:     operatively connected the transmit signal paths to a first antenna; and     operatively connected the receive signal paths to the second antenna so that the communication signals in the first transmit signal band and the communication signals in the first receive signal band are conveyed via different antenna.        
 
         [0040]     Advantageously, the method further comprises the step of impedance matching the plurality of receive signal paths.  
         [0041]     Advantageously, the method further comprises the step of providing a plurality of filters in the plurality of receive signal paths for filtering signals in corresponding frequency ranges.  
         [0042]     Advantageously, the method further comprises the step of providing a balun between the second antenna and each of said plurality of filters.  
         [0043]     Advantageously, the method further comprises the step of providing an isolation circuit in at least one of the receive signal paths for cross-band isolation between the transmitted communication signals and received communication signals.  
         [0044]     Advantageously, the method further comprises the step of providing a plurality of signal amplifiers in the plurality of receive signal paths for cross-band isolation between the transmitted communication signals and the receive communication signals.  
         [0045]     According to the third aspect of the present invention, there is provided a portable communication device, comprising: 
        at least a first antenna;     a second antenna electrically separating from the first antenna;     a transceive front-end module comprises a plurality of signal paths operatively connected to the first antenna for transmitting signals in at least a first transmit frequency band and a different second transmit frequency band; and     a receive front-end module comprising:     a feed point, operatively connected to the second antenna for receiving communication signals in the communication device, and     a plurality of receive signal paths, operatively connected to the feed point for receiving communication signals in a plurality of frequency bands, wherein said plurality of frequency bands includes at least     a first receive frequency band, which is partially overlapped with the first transmit frequency band in the transceive front-end module, and     a second receive frequency band, which is spaced from the first receive frequency band in frequency.        
 
         [0054]     The portable communication device can be a mobile terminal, a communicator device or the like.  
         [0055]     The present invention will become apparent upon reading the description taken in conjunction with  FIGS. 2   a  to  9 . 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0056]      FIG. 1   a  is a block diagram illustrating a GSM part of a prior art front-end module.  
         [0057]      FIG. 1   b  is a block diagram illustrating a W-CDMA part of the same prior art front-end module.  
         [0058]      FIG. 2   a  is a block diagram illustrating a GSM part of an embodiment of the front-end module, according to the present invention.  
         [0059]      FIG. 2   b  is a block diagram illustrating a mixed GSM/W-CDMA part of the front-end module of  FIG. 2   a.    
         [0060]      FIG. 3  is a block diagram illustrating a different embodiment of the GSM part of the front-end module, according to the present invention.  
         [0061]      FIG. 4   a  is a block diagram illustrating a mixed GSM/W-CDMA 2 GHz Tx module in combination with a 1 GHz GSM Tx/Rx module, according to the preferred embodiment of the present invention.  
         [0062]      FIG. 4   b  is a block diagram illustrating a mixed GSM/W-CDMA 2 GHz Rx module, according to the preferred embodiment of the present invention.  
         [0063]      FIG. 5   a  is a block diagram illustrating a different embodiment of the GSM/W-CDMA 2 GHz Rx module.  
         [0064]      FIG. 5   b  is a block diagram illustrating another embodiment of the GSM/W-CDMA 2 GHz Rx module.  
         [0065]      FIG. 6   a  is a schematic representation showing the Tx-Rx antenna isolation in GSM/W-CDMA front-end, according to the present invention.  
         [0066]      FIG. 6   b  is a frequency chart showing the overlapping in GSM and W-CDMA frequencies.  
         [0067]      FIG. 7   a  is a block diagram illustrating the use of switches to solve the cross-band isolation problem in the GSM/W-CDMA 2 GHz Rx module in a transceiver.  
         [0068]      FIG. 7   b  is a block diagram illustrating the use of low noise amplifier to solve the cross-band problem in the GSM/W-CDMA 2 GHz Rx module in a transceiver.  
         [0069]      FIG. 7   c  is a block diagram illustrating the single-antenna receive module of  FIG. 7   b  in a “WORLD” WCDMA EU/US2/IUS1 &amp; 1800/1900 GSM Rx combination.  
         [0070]      FIG. 8  is a block diagram illustrating a Diversity combination of two identical Rx modules.  
         [0071]      FIG. 9  is a schematic representation showing a mobile terminal having a transceiver front-end, according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0072]     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. 9 , 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 an antenna  20 . The second module  8  may have one or more antenna  20 ′ for Rx MIMO/diversity purposes.  
         [0073]     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. 2   a , 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. 1   a ) can be eliminated. The 1800GSM Rx path  220  shares the upper band antenna  20  of the W-CDMA module, as shown in  FIG. 2   b . 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. 1   a ). It should be noted that the switching as shown in  FIG. 2   a  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.  
         [0074]     A further improvement for reducing the losses of the 1900GSM Rx and the 1800 &amp; 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 (1850-1901 MHz). As such, the switching elements  46 ,  48  and  82  (see  FIG. 2   a ) 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.  
         [0075]     Moreover, the 1920-1980 MHz W-CDMA path  340  in the  FIG. 2   b  and the 1900GSM Rx path  240  in  FIG. 3  can change places, as shown  FIGS. 4   a  and  4   b . As shown in  FIG. 4   a , 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. 2   b ). As shown in  FIG. 4   b , 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.  
         [0076]     In the arrangement as shown in  FIGS. 4   a  and  4   b , 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. 2   a , the matching elements in  FIG. 4   a  can be replaced by CMOS or p-HEMT switches.  
         [0077]     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.  
         [0078]     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. 4   a  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. 4   b  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.  
         [0079]      FIGS. 5   a  and  5   b  shows different embodiments of the 2 GHz Rx module as shown in  FIG. 4   b . 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. 5   a , 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.  
         [0080]     When separate baluns  232 ,  252 ,  332  are used, as shown in  FIG. 4   b , 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. 5   b . 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. 4   b  and  5   a , 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 1 GHz 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.  
         [0081]     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 modern 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. 6   a  and  6   b  for the case involving 1800GSM, 1900GSM and the European W-CDMA.  
         [0082]     As shown in  FIG. 6   a , the upper band Tx chain connected to the antenna  10  includes 1800GSM Tx — 3 (1710-1785 MHz): 1900GSM Tx — 4 (1850-1910 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. 6   b . 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.  
         [0083]     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. 7   a . 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. 7   a , 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 .  
         [0084]     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.  
         [0085]     Cross-band isolation using LNAs is shown in  FIG. 7   b . 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.  
         [0086]     If the baluns in the Rx modules are not acoustic baluns, as those shown in  FIGS. 5   a ,  7   a  and  7   b , 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. 7   c . The receive module as shown in  FIG. 7   c  is a single-antenna module in a “WORLD” W-CDMA EU/US2/US1 and 1800/1900GSM Rx combination.  
         [0087]     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.  
         [0088]     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.  
         [0089]     In diversity, the only requirement is the duplicating of the module. For example, two identical Rx modules  601  can be used side-by-side, as shown in  FIG. 8 . In such case, only one Tx module ( FIG. 4   a , for example) is necessary.  
         [0090]     In the modules that contain upper band Tx paths, such as 1800 &amp; 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. 2   a , 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 4   a , 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. 4   a . 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.  
         [0091]     The 1GHz 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.  
         [0092]     The advantages of this invention are many (some may depend on the specific band combination and implementation): 
        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     Separate Rx and Tx antennas: for free Tx to Rx isolation, less stringent filtering requirements (especially in CDMA applications), smaller number of components.     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).     Modules having common footprint, I/O allocation may be used with only the internal die selected, depending on the build required.     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.     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.        
 
         [0099]     It should be noted that the W-CDMA modes have been described as W-CDMA EU, US1 and US2. However, the present invention is also applicable to any other W-CDMA modes currently existing and those to be developed in the future.  
         [0100]     Thus, 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.