Abstract:
A communication system for communicating CDMA and GSM transmit and receive RF information signals through one or more antennas is disclosed. The communication system is comprised of a transmitting unit, a receiving unit, and at least one antenna. The transmitting unit modulates and upconverts a transmit baseband information signal to generate a CDMA transmit RF information signal and a GSM transmit RF information signal. The receiving unit downconverts and demodulates a CDMA receive RF information signal and a GSM receive RF information signal to generate a receive baseband information signal. One or more antennas are coupled to the transmitting unit and receiving unit for transmitting the CDMA transmit RF information signal and the GSM transmit RF information signal, and receiving the CDMA receive RF information signal and the GSM receive RF information signal. The transmitting unit comprises a modulator for modulating a transmit IF LO frequency with the transmit baseband information signal to generate a transmit IF information signal. It also includes a plurality of upconverters for upconverting the transmit IF information signal with a GSM transmit RF LO frequency to generate a GSM transmit RF information signal, and for upconverting the transmit IF information signal with a CDMA transmit RF LO frequency to generate at least one CDMA transmit RF information signal. The receiving unit comprises a downconverter for downconverting a CDMA receive RF information signal with a receive RF LO frequency to generate a receive IF information signal, and for downconverting at least one GSM receive RF information signal with the receive RF LO frequency to generate a receive IF information signal. It also includes a demodulator for demodulating the receive IF information signal with a receive IF LO frequency to generate a receive baseband information signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates, generally, to communication systems and processes which use radio frequency (RF) transmitters and receivers (transceivers), and, in particular embodiments, to systems and processes for multi-mode, multi-band Code Division Multiple Access (CDMA) and Global System for Mobile (GSM) communication transceivers that share functional blocks to minimize size, weight, complexity, power consumption, and cost. 
     2. Description of Related Art 
     It has become increasingly important to minimize the size, weight, complexity, power consumption, and cost of various electronic devices, especially personal communication devices such as cellular telephones, personal pagers, cordless telephones, and the like. One way to minimize such characteristics is to minimize the number of components and functions required in the electronic device, or to perform multiple functions using the same components. However, personal communication devices such as cellular telephones often require complex circuitry with a number of power-inefficient components for performing particular functions. This is especially true in modern cellular communications, where several different communication standards are employed worldwide, and cellular telephones with the flexibility to operate under multiple communications standards are highly desirable from a consumer and manufacturing perspective. 
     For example, the GSM communication standard is a world-wide mode of digital cellular communication operating over three different frequency bands. GSM-900 operates in the 900 MHz frequency band and is currently used in Europe and Asia. DCS is another digital cellular standard based on GSM technology, operating in the 1800 MHz frequency band and also currently used in Europe and Asia. The United States uses PCS, a third digital cellular standard similar to DCS, but operating in the 1900 MHz band. GSM is currently used in approximately 154 countries, including the geographic areas of North Africa, India, China, Europe, the Middle East, and Taiwan. 
     However, GSM is not the only mode of cellular communication. CDMA is another mode of digital cellular communication operating in either the 900 or 1900 MHz band. CDMA is one of the most widely used modes of cellular communication in the United States, and is the most widely used mode of cellular communication in Korea. CDMA is also being used in China, India, and Taiwan. 
     With improved voice and data communications and political climates continuing to expand the world market, a “world telephone” capable of operating in many different countries would be of interest to international business travelers. Multi-mode, multi-band cellular telephones with shared functionality and an optimized architecture capable of operating under all of these standards afford consumers widespread applicability and allow manufacturers to benefit from the cost-efficiency of a common design. 
     However, multi-mode, multi-band cellular telephones such as combined CDMA/GSM telephones present a number of design challenges. Conventional single-band transmitters typically require two separate frequencies, a fixed intermediate frequency (IF) for modulation and a tunable RF for upconversion. Conventional single-band receivers also typically require two separate frequencies, a tunable RF for downconversion and a fixed IF for demodulation. Thus, a single-band cellular telephone may require as many as four different frequency sources. CDMA/GSM multi-band and multi-mode cellular telephones exacerbate the problem because the modulation, upconversion, downconversion, and demodulation processes for each band and mode may operate at different frequencies and amplitudes. Furthermore, the frequencies and amplitudes employed by each band and mode may require different filters and amplifiers for the transmit and receive function of each band. The design challenge of producing cellular telephones of minimal size, weight, complexity, power consumption, and cost is thus compounded by multi-mode, multi-band cellular telephones. 
     SUMMARY OF THE DISCLOSURE 
     Therefore, it is an object of embodiments of the present invention to provide a system and process for a multi-mode, multi-band CDMA and GSM communication transceiver that shares functional blocks to minimize size, weight, complexity, power consumption, and cost. 
     These and other objects are accomplished according to a communication system for communicating CDMA and GSM transmit and receive RF information signals through one or more antennas. The communication system is comprised of a transmitting unit, a receiving unit, and at least one antenna. The transmitting unit modulates and upconverts a transmit baseband information signal to generate a CDMA transmit RF information signal and a GSM transmit RF information signal. The receiving unit downconverts and demodulates a CDMA receive RF information signal and a GSM receive RF information signal to generate a receive baseband information signal. One or more antennas are coupled to the transmitting unit and receiving unit for transmitting the CDMA transmit RF information signal and the GSM transmit RF information signal, and receiving the CDMA receive RF information signal and the GSM receive RF information signal. 
     The transmitting unit comprises a modulator for modulating a transmit IF local oscillator frequency (LO) with the transmit baseband information signal to generate a transmit IF information signal. It also includes a plurality of upconverters for upconverting the transmit IF information signal with a GSM transmit RF LO to generate the GSM transmit RF information signal, and for upconverting the transmit IF information signal with a CDMA transmit RF LO to generate the CDMA transmit RF information signal. 
     The receiving unit comprises a downconverter for downconverting the CDMA receive RF information signal with a receive RF LO to generate a receive IF information signal, and for downconverting the GSM receive RF information signal with the receive RF LO to generate a receive IF information signal. It also includes a demodulator for demodulating the receive IF information signal with a receive IF LO to generate the receive baseband information signal. 
     A transmit IF variable gain amplifier is coupled between the modulator and the plurality of upconverters for amplifying the transmit IF information signal. The plurality of upconverters includes a translation loop for upconverting the transmit IF information signal with the GSM transmit RF LO, and an upconverter mixer for upconverting the transmit IF information signal with the CDMA transmit RF LO. 
     These and other objects, features, and advantages of embodiments of the to invention will be apparent to those skilled in the art from the following detailed description of embodiments of the invention, when read with the drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is block diagram representation of a system environment according to an example embodiment of the present invention. 
     FIG. 2 is a more detailed block diagram representation of the modulator in the system of FIG.  1 . 
     FIG. 3 is a block diagram representation of a shared functional block CDMA-1900 and GSM-900 communication transceiver according to an embodiment of the present invention. 
     FIG. 4 is a block diagram representation of a shared functional block CDMA-900 and GSM-900 communication transceiver according to an embodiment of the present invention. 
     FIG. 5 is a block diagram representation of a shared functional block CDMA-1900 and PCS communication transceiver according to an embodiment of the present invention. 
     FIG. 6 is a block diagram representation of a shared functional block CDMA-1900 and PCS communication transceiver according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following description of preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the preferred embodiments of the present invention. 
     Cellular communication systems employ several different communication standards worldwide and utilize several different frequency bands. For example, the GSM communication standard operates over three different bands, 900 MHz, 1800 MHz, and 1900 MHz, while the CDMA communication standard operates over two different bands, 900 MHz and 1900 MHz. Multi-mode, multi-band cellular telephones, with the flexibility to operate under multiple communications standards, afford consumers widespread applicability and allow manufacturers to benefit from the cost-efficiency of a common design. 
     To realize a cost-efficient design, multi-mode, multi-band cellular telephones must minimize size, weight, complexity, and power consumption. Embodiments of the present invention therefore relate to multi-mode, multi-band cellular communication transceivers that share frequency sources, amplifiers, and mixers between bands and modes. It should be noted, however, that transceivers according to embodiments of the present invention are not unique to cellular communications and may be employed in a variety of communications electronics, including wireless transmission systems as well as wired systems. Thus, embodiments of the invention described herein may involve various forms of communications systems. However, for purposes of simplifying the present disclosure, preferred embodiments of the present invention are described herein in relation to personal wireless communications systems, including, but not limited to digital mobile telephones, digital cordless telephones, digital pagers, combinations thereof, and the like. Such personal communications systems typically include one or more portable or remotely located receiver and/or transmitter units. 
     Regardless of the form of the communication system, embodiments of the present invention combine two communication modes, GSM and CDMA. In CDMA-900, frequency bands are allocated such that a mobile subscriber unit will transmit signals over a transmit band of about 824-849 MHz and receive signals over a receive band of about 869-894 MHz. In CDMA-1900, frequency bands are allocated such that a mobile subscriber unit will transmit signals over a transmit band of about 1850-1910 MHz and receive signals over a receive band of about 1930-1990 MHz. Note that CDMA functional blocks employed in embodiments of the present invention should conform to Telecommunications Industry Association (TIA)/Electronic Industry Association (EIA)/Interim Standard (IS) “CDMA-900” (TIA/EIA/IS-95-A and TIA/EIA/IS-98-A), and American National Standards Institute, Inc. (ANSI) “CDMA-1900” (J-STD-018), standards that are well understood by those skilled in the art. These standards are incorporated herein by reference. 
     GSM is used herein to refer generally to three different applications of the GSM communication standard, GSM-900, DCS, and PCS. In GSM-900, frequency bands are allocated such that a mobile subscriber unit will transmit signals over a transmit band of between about 890 and 915 MHz and will receive signals over a receive band of between about 935 to 960 MHz. The transmit band is broken up into 125 channels, each channel separated by 200 kHz. In DCS, frequency bands are allocated such that a mobile subscriber unit will transmit signals over a transmit band of between about 1710 and 1785 MHz and will receive signals over a receive band of between about 1805 and 1880 MHz. The transmit band is broken up into 375 channels, each channel separated by 200 kHz. In PCS, frequency bands are allocated such that a mobile subscriber unit will transmit signals over a transmit band of between about 1850 and 1910 MHz and will receive signals over a receive band of between about 1930 and 1990 MHz. The transmit band is broken up into 300 channels, each channel separated by 200 kHz. It should be noted that GSM functional blocks employed in embodiments of the present invention conform to European Telecommunications Standards Institute (ETSI) “GSM-900 &amp; DCS-1800” (GSM 05.05, GSM 11.10-1, and TBR  5 ) and American National Standards Institute, Inc. (ANSI) “GSM-1900” (J-STD-007 Volumes 0-7), standards that are well understood by those skilled in the art. These standards are incorporated herein by reference. 
     Thus, embodiments of the present invention include the following GSM/CDMA combinations: CDMA-900 and CSM-900, CDMA-900 and DCS, CDMA-900 and PCS, CDMA-1900 and CSM-900, CDMA-1900 and DCS, and CDMA-1900 and PCS. It should be noted, however, that although the illustrated embodiments are limited to dual-mode, dual-band transceivers, alternative embodiments of the present invention include multi-mode, multi-band transceivers such as a combined CDMA-1900, PCS, and DCS transceiver. In such an embodiment, the PCS and DCS transmit and receive paths may contain paralleled filters to accommodate the relatively slight frequency differences between PCS and DCS. 
     A generalized representation of a communication system according to an embodiment of the present invention is shown in FIG. 1, wherein a transceiver  10  includes a transmitting unit  12  and a receiving unit  14 , coupled for communication over a communication channel  42 . Transmitting unit  12  includes a modulator  16  coupled to receive a transmit baseband information signal  18  from a signal source (not shown in FIG.  1 ). In one representative embodiment, the signal source may include, for example, a microphone for converting sound waves into electronic signals and sampling and analog-to-digital converter electronics for sampling and converting the electronic signals into digital signals representative of the sound waves. In other embodiments, the signal source may include any suitable device for producing digital data signals for communication over channel  42 , such as, but not limited to, a keyboard, a digital voice encoder, a mouse or other user input device, a sensor, monitor or testing apparatus, or the like. 
     Modulator  16  provides a transmit IF information signal  32  as an output to a transmitter  20 . A transmit RF information signal  26  is produced by transmitter  20  for transmission from an antenna  22 . Receiving unit  14  includes a receiver  24  coupled to an antenna  22  to process a receive RF information signal  44 . Receiver  24  provides a modulated receive IF information signal  34  to a demodulator  28 , which demodulates receive IF information signal  34  and generates receive baseband information signals  46 . 
     The demodulated receive baseband information signals  46  from demodulator  28  may be provided to signal processing electronics, sound producing electronics or the like, depending upon the nature of use of the transceiver  10 . The transmitting and receiving units  12  and  14  include further components, power supplies, and the like, well known in the art for effecting transmission and reception of signals and for carrying out other functions specific to the nature and application of use of the transceiver  10 . 
     In preferred transceiver embodiments, such as cellular telephone embodiments or cordless telephone embodiments, each transmitting unit  12  and receiving unit  14  is configured to function as both a transmitting unit and a receiving unit. In one system embodiment, transmitting unit  12  and receiving unit  14  transmit and receive signals directly therebetween. In other system embodiments, transmitting unit  12  and receiving unit  14  communicate through one or more additional transceiver stations  30  (such as repeaters, base or cell stations, or the like). 
     As illustrated in the modulator  16  of FIG. 2, in digital cellular telephone or to cordless telephone system embodiments transmit baseband information signal  18  provides sampled voice (or sound) signals in the form of baseband I and Q channel signals to an encoder  36 . In one preferred cellular telephone embodiment, encoder  36  comprises a Phase Shift Key encoder, such as, but not limited to, a π/4-shift Quadrature Phase Shift Key mapper with differential encoder (π/4 DQPSK), and shaping filters  38  comprise pulse shaping filters for smoothing the encoder output signal. An example of a π/4 DQPSK and pulse shaping electronics is described in the article titled: “π/4-shift QPSK Digital Modulator LSIC for Personal Communication Terminals,” by Tetsu Sakata, Kazuhiko Seki, Shuji Kubota and Shuzo Kato, Proc. 5th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 1994 (incorporated herein by reference). Other embodiments may employ other suitable encoding schemes, including but not limited to Amplitude Shift Keying and Frequency Shift Keying schemes. 
     I and Q outputs of the encoder pass through shaping filters  38  and then to frequency conversion and modulation electronics  40 , the output of which comprises a transmit IF information signal  32 . Transmit IF information signal  32  is then fed to transmitter  20  as shown in FIG. 1, which provides the transmit RF information signal  26  to the antenna  22  for transmission. 
     A shared functional block CDMA-1900 and CSM-900 communication transceiver  48  according to an embodiment of the present invention is illustrated in FIG.  3 . The transceiver  48  includes a modulator  16  as described above with reference to FIG.  2 . In the transmit path, frequency conversion and modulation electronics  40  receive the I and Q outputs of shaping filters  38  and modulate a transmit IF LO  50  with the I and Q outputs to produce a transmit IF information signal  32  at an IF carrier frequency. Transmit IF LO  50  is generated by a transmit IF LO frequency generator  52  comprising a CDMA transmit IF LO frequency source  54  phase-locked to a reference source  58  by transmit IF LO loop electronics  56 . In preferred embodiments of the present invention, CDMA transmit IF LO frequency source  54  is a voltage controlled oscillator (VCO). However, in alternative embodiments of the present invention, CDMA transmit IF LO frequency source  54  may be any adjustable frequency source. 
     Transmit IF information signal  32  is then amplified by a transmit IF variable gain amplifier (VGA)  60  within transmitter  20 , which adjusts its gain based on commands received from the base station. It should be noted that although a variable gain amplifier is not required for GSM, power control is critical in CDMA, and thus because transmit IF VGA  60  is shared between the CDMA and GSM receive paths, transmit IF VGA  60  must have variable gain capability to meet the power control requirements of CDMA. 
     The output of transmit IF VGA  60  is split by first transmit IF power splitter  208 , and in the CDMA-1900 transmit path is then filtered by CDMA transmit IF filter  62 , which filters out noise generated by the transmit IF VGA  60  in the receive band to meet receive band noise floor requirements. CDMA transmit IF filter  62  has a center frequency approximately equivalent to the IF carrier frequency and a bandwidth sufficient to pass the modulated and amplified transmit IF information signal with minimal distortion. CDMA has a modulation bandwidth of 1.25 MHz, thus the bandwidth of CDMA transmit IF filter  62  must be at least 1.25 MHz. In preferred embodiments, the bandwidth of CDMA transmit IF filter  62  is about 5 MHz. The modulated, amplified, and filtered transmit IF information signal is then mixed with a CDMA transmit RF LO  64  in CDMA transmit upconverter mixer  66 . In preferred embodiments, CDMA transmit upconverter mixer  66  generates the difference between the output of CDMA transmit IF filter  62  and CDMA transmit RF LO  64 . 
     In embodiments of the present invention, CDMA transmit RF LO  64  is generated by a CDMA RF LO frequency generator  68  containing a CDMA RF LO frequency source  70  phase-locked to reference source  58  by CDMA RF LO loop electronics  72 . In preferred embodiments, CDMA RF LO frequency source  70  comprises a VCO. However, in alternative embodiments, CDMA RF LO frequency source  70  may be any adjustable frequency source. 
     The output of CDMA transmit upconverter mixer  66  is filtered by first CDMA transmit RF filter  74  which, in the CDMA-1900 example of FIG. 3, has a passband encompassing the CDMA-1900 transmit band of about 1850-1910 MHz to remove spurious frequencies generated by CDMA transmit upconverter mixer  66 . The output of first CDMA transmit RF filter  74  is then amplified by CDMA transmit RF driver amplifier  76 . The output of CDMA transmit RF driver amplifier  76  is then filtered by second CDMA transmit RF filter  78 , which in the CDMA-1900 example of FIG. 3 has a passband encompassing the CDMA-1900 transmit band of about 1850-1910 MHz to filter out noise in the CDMA-1900 receive band generated by CDMA transmit RF driver amplifier  76 . The output of second CDMA transmit RF filter  78  is then amplified by CDMA transmit RF power amplifier  80  to generate CDMA transmit RF information signal  26  at a level sufficient to meet output power requirements at antenna  22 . CDMA transmit RF information signal  26  is then filtered by duplexer  82 , which in the CDMA-1900 example of FIG. 3 has a transmit passband encompassing the CDMA-1900 transmit band of about 1850-1910 MHz to filter out-of-band noise generated by CDMA transmit RF power amplifier  80 . The output of duplexer  82  then passes through mode select switch  84  within antenna coupling electronics  86  before being transmitted by antenna  22 . In alternative embodiments of the present invention, mode select switch  84  may be an RF switch, a resistor combiner, or a duplexer. 
     In the CDMA-1900 receive path, signals from antenna  22  enter antenna coupling electronics  86 , where they pass through mode select switch  84  and are filtered by duplexer  82  having a receive passband approximately equivalent to the CDMA-1900 receive band of about 1930-1990 MHz for passing only CDMA-1900 receive band signals. The output of duplexer  82  is CDMA receive RF information signal  88 . 
     CDMA receive RF information signal  88  is then amplified by a CDMA receive RF LNA  90 . The output of CDMA receive RF LNA  90  is then filtered by a CDMA receive RF image reject filter  92 . CDMA receive RF image reject filter  92  is a bandpass filter with a passband approximately equivalent to the CDMA-1900 receive band of about 1930-1990 MHz to filter out image noise generated by CDMA receive RF LNA  90  capable of mixing with CDMA receive RF LO  94  in CDMA receive downconverter mixer  96  and producing unwanted signals in the IF band. In preferred embodiments of the present invention, CDMA receive RF LO  94  is generated by CDMA RF LO frequency generator  68 , and CDMA receive downconverter mixer  96  generates the difference between the output of CDMA receive RF image reject filter  92  and CDMA receive RF LO  94 , designated herein as CDMA receive IF information signal  102 . It should be noted that in alternative embodiments of the present invention, active image cancellation such as an image reject mixer may be employed, eliminating the need for CDMA receive RF image reject filter  92 . 
     CDMA receive IF information signal  102  then passes through a CDMA receive IF filter  98  with a bandwidth approximately equivalent to the CDMA modulation bandwidth of 1.25 MHz to remove spurious frequencies generated by CDMA receive downconverter mixer  96 . The output of CDMA receive IF filter  98  is then coupled to receive IF VGA  100  through a first receive IF switch  206 . Receive IF VGA  100  provides variable gain control by adjusting its gain based on commands received from the base station. The output of receive IF VGA  100  is receive IF information signal  34 . 
     Receive IF information signal  34  is mixed with receive IF LO  116  and demodulated by frequency conversion and demodulation electronics  104  within demodulator  28 . In embodiments of the present invention, receive IF LO  116  is generated by a receive IF LO frequency generator  112  comprising a CDMA receive IF LO frequency source  110  phase-locked to reference source  58  by receive IF LO loop electronics  114 . In preferred embodiments, CDMA receive IF LO frequency source  110  is a VCO. However, in alternative embodiments, CDMA receive IF LO frequency source  110  may be any adjustable frequency source. 
     Frequency conversion and demodulation electronics  104  produce baseband information signals  120 , characterized herein as either DC or a “near DC” IF (for example, a center frequency above about 1 MHz). In the CDMA-1900 receive path, these baseband information signals  120  are filtered by CDMA baseband filters  106  to remove spurious frequencies generated by frequency conversion and demodulation electronics  104 . CDMA baseband filters  106  have a bandwidth of about 1.25 MHz to accommodate the modulation bandwidth of CDMA receive baseband signals, and may be low pass filters if the receive baseband signals are DC, or bandpass filters if the receive baseband signals are near DC. The filtered and demodulated receive baseband signals are then processed by quantizers  108 , which generate CDMA I and Q outputs  122 . In preferred embodiments, quantizers  108  are analog-to-digital converters (ADCs). 
     The CSM-900 transmit path shares modulator  16  and transmit IF VGA  60  with the CDMA-1900 transmit path. However, transmit IF LO  50 , used by frequency conversion and modulation electronics  40  to generate transmit IF information signal  32 , is produced by GSM transmit IF LO frequency source  126  within transmit IF LO frequency generator  52 . GSM transmit IF LO frequency source  126  is coupled in parallel with CDMA transmit IF LO frequency source  54  and is phase-locked to reference source  58  by transmit IF LO loop electronics  56 . 
     The CSM-900 transmit path diverges from the CDMA-1900 transmit path at the output of transmit IF VGA  60 , where the output of transmit IF VGA  60  is split by first transmit IF power splitter  208  and filtered by GSM transmit IF filter  128 , which filters out noise generated by the transmit IF VGA  60  in the GSM receive band to meet receive band noise floor requirements. GSM transmit IF filter  128  has a center frequency approximately equivalent to the:IF carrier frequency and a bandwidth sufficient to pass the modulated and amplified-transmit IF information signal with minimal distortion. GSM has a modulation bandwidth of 200 kHz, thus the bandwidth of GSM transmit IF filter  128  must be at least 200 kHz. In preferred embodiments, the bandwidth of GSM transmit IF filter  128  is about 1 MHz. 
     In preferred embodiments of the present invention, the output of GSM transmit IF filter  128  is then upconverted by a translation loop  130 . In further preferred embodiments, translation loop  130  includes a GSM VCO  132  coupled to a translation loop mixer  134  and phase-locked to a GSM transmit RF LO  136  for generating GSM RF carrier frequencies. Translation loop  130  acts like a tracking filter with a center. frequency at the frequency of the GSM VCO  132 . 
     In embodiments of the present invention, GSM transmit RF LO  136  is generated by a GSM RF LO frequency generator  138  comprising a GSM RF LO frequency source  140  phase-locked to reference source  58  by GSM RF LO loop electronics  142 . In preferred embodiments, GSM RF LO frequency source  140  comprises a VCO. However, in alternative embodiments, GSM RF LO frequency source  140  may be any adjustable frequency source. 
     In preferred embodiments, translation loop mixer  134  generates the difference between GSM VCO  132  and GSM transmit RF LO  136 . Translation loop  130  further includes a feedback filter  144  for filtering the output of translation loop mixer  134  to remove mixer noise, a phase detector  146  for determining the phase difference between the output of feedback filter  144  and GSM transmit IF filter  128 , a charge pump  148  for sourcing or sinking current as determined by the phase difference output of phase detector  146 , and a loop filter  150  for integrating current pulses from charge pump  148  and providing a control voltage  152  to GSM VCO  132 . 
     The modulated, upconverted output of GSM VCO  132  is then amplified by GSM transmit RF power amplifier  154  to generate a GSM transmit RF information signal at a level sufficient to meet output power requirements at antenna  22 . The output of GSM transmit RF power amplifier  154  is then filtered by GSM transmit RF filter  156 , which in the CSM-900 example of FIG. 3 has a transmit passband encompassing the CSM-900 transmit band of about 890-915 MHz to filter out-of-band noise generated by GSM transmit RF power amplifier  154 . The output of GSM transmit RF filter  156 , identified herein as GSM transmit RF information signal  204 , then passes through transmit/receive switch  158  within antenna coupling electronics  86  and mode select switch  84  before being transmitted by antenna  22 . In alternative embodiments of the present invention, transmit/receive switch  158  may be an RF switch, a resistor combiner, or a duplexer. 
     It should be noted that because translation loop  130  in the GSM transmit path generates a relatively clean (minimal out-of-band noise) signal from GSM VCO  132 , there is no need for a high-insertion loss duplexer, as used in the CDMA transmit path. The elimination of the duplexer enables a lower power GSM transmit RF power amplifier to be used, resulting in substantial power savings in the communication transceiver. The CDMA transmit path cannot use a translation loop, however, because a translation loop cannot track the amplitude information present in a CDMA Offset QPSK (OQPSK) signal. 
     Notwithstanding the advantages of using a translation loop, in alternative embodiments of the present invention translation loop  130  may be replaced by an upconverter mixer as in the CDMA transmit path. In such embodiments, transmit/receive switch  158  may be replaced with a duplexer to filter out-of-band noise generated by GSM transmit RF power amplifier  154 . 
     In the CSM-900 receive path, signals from antenna  22  enter antenna coupling electronics  86 , where they pass through mode select switch  84  and transmit/receive switch  158 . The output of transmit/receive switch  158  is GSM receive RF information signal  162 , which is filtered by preselector filter  164  having a receive passband approximately equivalent to the CSM-900 receive band of about 935-960 MHz for passing only CSM-900 receive band signals. 
     The output of preselector filter  164  is then amplified by a GSM receive RF LNA  166 . The output of GSM receive RF LNA  166  is then filtered by a GSM receive RF image reject filter  168 . GSM receive RF image reject filter  168  is a bandpass filter with a bandwidth approximately equivalent to the CSM-900 receive band of about 935-960 MHz to filter out image noise generated by GSM receive RF LNA  166  capable of mixing with GSM receive RF LO  170  in GSM receive downconverter mixer  172  and producing unwanted signals in the IF band. In preferred embodiments of the present invention, GSM receive RF LO  170  is generated by GSM RF LO frequency generator  138 , and GSM receive downconverter mixer  172  generates the difference between the output of GSM receive RF image reject filter  168  and GSM receive RF LO  170 , designated herein as GSM receive IF information signal  174 . It should be noted that in alternative embodiments of the present invention, active image cancellation such as an image reject mixer may be employed, eliminating the need for GSM receive RF image reject filter  168 . 
     GSM receive IF information signal  174  then passes through a GSM receive IF filter  176  with a bandwidth approximately equivalent to the GSM modulation bandwidth of 200 kHz to remove spurious frequencies generated by GSM receive downconverter mixer  172 . 
     The output of GSM receive IF filter  176  is then coupled to receive IF VGA  100  by first receive IF switch  206 , where it is amplified by receive IF VGA  100 . However, as previously noted, the output of CDMA receive IF filter  98  is also coupled to receive IF VGA  100  by first receive IF switch  206 . Thus, the gain, NF, and IIP 3  of the shared receive IF VGA  100  must be chosen to satisfy the requirements of both the CDMA-1900 and CSM-900 receive paths. In alternative embodiments of the present invention, first receive IF switch  206  may comprise a switchable high off-state impedance buffer amplifiers or an RF switch. 
     Receive IF information signal  34  is then mixed with receive IF LO  116  and demodulated by frequency conversion and demodulation electronics  104  within demodulator  28 . Because the IF frequencies of CDMA-1900 and CSM-900 may be different, receive IF LO  116  as used for GSM demodulation is not generated by CDMA receive IF LO frequency source  110 . Instead, receive IF LO  116  as used for GSM demodulation is generated by a GSM receive IF LO frequency source  160  in parallel with CDMA receive IF LO frequency source  110  and phase-locked to reference source  58  by receive IF LO loop electronics  114 . In preferred embodiments of the present invention, GSM receive IF LO frequency source  160  is a VCO. However, in alternative embodiments, GSM receive IF LO frequency source  160  may be any adjustable frequency source. 
     Frequency conversion and demodulation electronics  104  produce baseband information signals  120 . In the CSM-900 receive path, these baseband information signals  120  are filtered by GSM baseband filters  118  to remove spurious frequencies generated by frequency conversion and demodulation electronics  104 . GSM baseband filters  118  have a bandwidth of about 200 kHz to accommodate the modulation bandwidth of GSM receive baseband signals, and may be low pass filters if the receive baseband signals are DC, or bandpass filters if the receive baseband signals are near DC. The filtered and demodulated receive baseband signals are then processed by quantizers  108 , which generate GSM I and Q outputs  124 . In preferred embodiments, quantizers  108  are analog-to-digital converters (ADCs). 
     In embodiments of the present invention, mode selector electronics  178  configures the CDMA-1900 and CSM-900 communication transceiver  48  for either CDMA or GSM operation. In preferred embodiments of the present invention, mode selector electronics  178  is a processing device automatically configurable by remote commands or signal strength measurements received from base stations. In alternative embodiments, mode selector electronics  178  may comprise a factory-programmable logic device or user-configurable logic. When mode selector electronics  178  is configured for CDMA operation, mode select switch  84  is configured to couple duplexer  82  to antenna  22 , receive IF LO frequency generator  112  is configured to couple CDMA receive IF LO frequency source  110  to frequency conversion and demodulation electronics  104 , and transmit IF LO frequency generator  52  is configured to couple CDMA transmit IF LO frequency source  54  to frequency conversion and modulation electronics  40 . When mode selector electronics  178  is configured for GSM operation, mode select switch  84  is configured to couple transmit/receive switch  158  to antenna  22 , receive IF LO frequency generator  112  is configured to couple GSM receive IF LO frequency source  160  to frequency conversion and demodulation electronics  104 , and transmit IF LO frequency generator  52  is configured to couple GSM transmit IF LO frequency source  126  to frequency conversion and modulation electronics  40 . 
     Embodiments of the present invention described above employ a separate CDMA transmit IF LO frequency source  54  and GSM transmit IF LO frequency source  126 . However, in alternative embodiments of the present invention, CDMA transmit IF LO frequency source  54  and GSM transmit IF LO frequency source  126  may comprise a single tunable transmit IF LO frequency source. Similarly, embodiments of the present invention described above disclose a separate CDMA receive IF LO frequency source  110  and GSM receive IF LO frequency source  160 . However, in alternative embodiments of the present invention, CDMA receive IF LO frequency source  110  and GSM receive IF LO frequency source  160  may comprise a single tunable receive IF LO frequency source. 
     Furthermore, embodiments of the present invention described above employ a single CDMA RF LO frequency source  70 . However, in alternative embodiments of the present invention, CDMA RF LO frequency source  70  may comprise a separate CDMA receive RF LO frequency source and a separate CDMA transmit RF LO frequency source. Similarly, embodiments of the present invention described above disclose a single GSM RF LO frequency source  140 . However, in alternative embodiments of the present invention, GSM RF LO frequency source  140  may comprise a separate GSM receive RF LO frequency source and a separate GSM transmit RF LO frequency source. 
     A shared functional block CDMA-900 and CSM-900 communication transceiver  180  according to an embodiment of the present invention is illustrated in FIG.  4 . The architecture and operation of CDMA-900 and CSM-900 communication transceiver  180  in FIG. 4 is similar to that of CDMA-1900 and CSM-900 communication transceiver  48  in FIG. 3, except as noted below. Referring to FIG. 4, in the CDMA receive path, CDMA receive RF information signal  88  passes through a variable gain attenuator  182  in preferred embodiments of the present invention. Unlike the CDMA-1900 communication standard, which only specifies one composite signal level for purposes of test, the CDMA-900 communication standard specifies three different composite signals for purposes of test, and thus variable gain attenuator  182  selectively attenuates the received signal to meet CDMA communication standard cellular receive band intermodulation requirements. However, in alternative embodiments, attenuation control may be achieved by selectively bypassing common receive RF LNA  184 , or a variable gain common receive RF LNA  184  may be employed instead of variable gain attenuator  182 . 
     The output of variable gain attenuator  182  in the CDMA receive path and preselector filter  164  in the GSM receive path are coupled by a first receive RF switch  186 , which, in alternative embodiments of the present invention, may be an RF switch, high off-state impedance amplifiers or transmission gates, a resistor combiner, or a duplexer. First receive RF switch  186  allows common receive RF LNA  184  to be used in both the CDMA and GSM receive paths. The use of a single, limited frequency range LNA is possible in CDMA-900 and CSM-900 communication transceiver  180  because the frequency bands of CDMA-900 and CSM-900 are similar. Because common receive RF LNA  184  is shared between the CDMA-900 and CSM-900 receive paths, the gain, NF, and IIP 3  of common receive RF LNA  184  must be chosen to satisfy the requirements of both the CDMA-900 and CSM-900 receive paths. The output of common receive RF LNA  184  is then coupled to either CDMA receive RF image reject filter  92  or GSM receive RF image reject filter  168  by second receive RF switch  188 . In alternative embodiments of the present invention, second receive RF switch  188  may be an RF switch, high off-state impedance amplifiers or transmission gates, a resistor combiner, or a duplexer. 
     The outputs of CDMA receive RF image reject filter  92  and GSM receive RF image reject filter  168  are then coupled to common receive downconverter mixer  190  by third receive RF switch  192 . Third receive RF switch  192  allows common receive downconverter mixer  190  to be used in both the CDMA and GSM receive paths, which is possible because of the small frequency difference between the receive bands of CDMA-900 and CSM-900. Because common receive downconverter mixer  190  is shared between the CDMA-900 and CSM-900 receive paths, the gain, NF, and IIP 3  of common receive downconverter mixer  190  must be chosen to satisfy the requirements of both the CDMA-900 and CSM-900 receive paths. In alternative embodiments of the present invention, third receive RF switch  192  may be an RF switch, high off-state impedance amplifiers or transmission gates, a resistor combiner, or a duplexer. Downconverter mixer  190  mixes either the output of CDMA receive RF image reject filter  92  or the output of GSM receive RF image reject filter  168  with a common receive RF LO  194 . 
     Common receive RF LO  194  is produced by coupling CDMA RF LO frequency source  70  and GSM RF LO frequency source  140  with a common receive RF LO power combiner  200 . The output of common receive RF LO power combiner  200  is approximately equivalent to either the output of CDMA RF LO frequency source  70  or the output of GSM RF LO frequency source  140 , because mode selector electronics  178  enables either CDMA RF LO frequency source  70  or GSM RF LO frequency source  140 , but not both. 
     The output of downconverter mixer  190  is coupled to CDMA receive IF filter  98  and GSM receive IF filter  176  through common receive IF power splitter  202 , which distributes a signal approximately equal in amplitude and phase to CDMA receive IF filter  98  and GSM receive IF filter  176 . In preferred embodiments, CDMA receive IF filter  98  and GSM receive IF filter  176  are surface acoustic wave (SAW) filters, because SAW filters act as high impedance elements for out-of-band frequencies. The outputs of CDMA receive IF filter  98  and GSM receive IF filter  176  are coupled to receive IF VGA  100  by first receive IF switch  206 . Because receive IF VGA  100  is shared between the CDMA-900 and CSM-900 receive paths, the gain, NF, and IIP 3  of receive IF VGA  100  must be chosen to satisfy the requirements of both the CDMA-900 and CSM-900 receive paths. 
     When mode selector electronics  178  is configured for CDMA operation, first receive RF switch  186  is configured to couple variable gain attenuator  182  to common receive RF LNA  184 , second receive RF switch  188  is configured to couple common receive RF LNA  184  to CDMA receive RF image reject filter  92 , and third receive RF switch  192  is configured to couple CDMA receive RF image reject filter  92  to common to receive downconverter mixer  190 . When mode selector electronics  178  is configured for GSM operation, first receive RF switch  186  is configured to couple preselector filter  164  to common receive RF LNA  184 , second receive RF switch  188  is configured to couple common receive RF LNA  184  to GSM receive RF image reject filter  168 , and third receive RF switch  192  is configured to couple GSM receive RF image reject filter  168  to common receive downconverter mixer  190 . 
     It should also be noted that the RF filters in the CDMA transmit and receive paths of CDMA-900 and CSM-900 communication transceiver  180  have different passbands as compared to those in FIG.  3 . First CDMA transmit RF filter- 74 , second CDMA transmit RF filter  78 , and duplexer  82  have transmit passbands encompassing the CDMA-900 transmit band of about 824-849 MHz. Duplexer  82  and CDMA receive RF image reject filter  92  have receive passbands approximately equivalent to the CDMA-900 receive band of about 869-894 MHz. 
     A shared functional block CDMA-900 and PCS communication transceiver  196  according to an embodiment of the present invention is illustrated in FIG.  5 . It should be noted that a similar architecture is applicable to a shared functional block CDMA-900 and DCS communication transceiver. The architecture and operation of CDMA-900 and PCS communication transceiver  196  in FIG. 5 is similar to that of CDMA-1900 and CSM-900 communication transceiver  48  in FIG. 3, except that in the CDMA receive path, variable gain attenuator  182  is coupled between duplexer  82  and CDMA receive RF LNA  90 . Note that because receive IF VGA  100  is shared by the CDMA-900 and PCS receive paths, the gain, NF, and IIP 3  of the shared receive IF VGA  100  must be chosen to satisfy the requirements of both the CDMA-900 and PCS receive paths. 
     It should also be noted that the RF filters in the CDMA and GSM transmit and receive paths of CDMA-900 and PCS communication transceiver  196  have different passbands as compared to those in FIG.  3 . First CDMA transmit RF filter  74 , second CDMA transmit RF filter  78 , and duplexer  82  have transmit passbands encompassing the CDMA-900 transmit band of about 824-849 MHz. Duplexer  82  and CDMA receive RF image reject filter  92  have receive passbands approximately equivalent to the CDMA-900 receive band of about 869-894 MHz. GSM transmit RF filter  156  has a transmit passband encompassing the PCS transmit band of about 1850-1910 MHz. Preselector filter  164  and GSM receive RF image reject filter  168  have receive passbands approximately equivalent to the PCS receive band of about 1930-1990 MHz. 
     Furthermore, in alternative embodiments of the present invention wherein the DCS communication standard replaces the PCS communication standard in FIG. 5, GSM transmit RF filter  156  has a transmit passband encompassing the DCS transmit band of about 1710-1785 MHz, and preselector filter  164  and GSM receive RF image reject filter  168  have receive passbands approximately equivalent to the DCS receive band of about 1805-1880 MHz. 
     A shared functional block CDMA-1900 and PCS communication transceiver  198  according to an embodiment of the present invention is illustrated in FIG.  6 . It should be noted that a similar architecture is applicable to a shared functional block CDMA-1900 and DCS communication transceiver. The architecture and operation of CDMA-1900 and PCS communication transceiver  198  in FIG. 6 is similar to that of CDMA-1900 and CSM-900 communication transceiver  48  in FIG. 3, except that the output of duplexer  82  in the CDMA receive path and preselector filter  164  in the GSM receive path are coupled by a first receive RF switch  186 , which, in alternative embodiments of the present invention, may be an RF switch, high off-state impedance amplifiers or transmission gates, a resistor combiner, or a duplexer. First receive RF switch  186  allows common receive RF LNA  184  to be used in both the CDMA and GSM receive paths. The use of a single, limited frequency range LNA is possible in CDMA-1900 and PCS communication transceiver  198  because the frequency bands of CDMA-1900 and PCS are similar. Because common receive RF LNA  184  is shared between the CDMA-1900 and PCS receive paths, the gain, NF, and IIP 3  of common receive RF LNA  184  must be chosen to satisfy the requirements of both the CDMA-1900 and PCS receive paths. The output of common receive RF LNA  184  is then coupled to either CDMA receive RF image reject filter  92  or GSM receive RF image reject filter  168  by second receive RF switch  188 . In alternative embodiments of the present invention, second receive RF switch  188  may be an RF switch, high off-state impedance amplifiers or transmission gates, a resistor combiner, or a duplexer. 
     The outputs of CDMA receive RF image reject filter  92  and GSM receive RF image reject filter  168  are then coupled to common receive downconverter mixer  190  by third receive RF switch  192 . Third receive RF switch  192  allows common receive downconverter mixer  190  to be used in both the CDMA and GSM receive paths, which is possible because of the small frequency difference between the receive bands of CDMA-1900 and PCS. Because common receive downconverter mixer  190  is shared between the CDMA-1900 and PCS receive paths, the gain, NF, and IIP 3  of common receive downconverter mixer  190  must be chosen to satisfy the requirements of both the CDMA-1900 and PCS receive paths. In alternative embodiments of the-present invention, third receive RF switch  192  may be an RF switch, high off-state impedance amplifiers or transmission gates, a resistor combiner, or a duplexer. Downconverter mixer  190  mixes either the output of CDMA receive RF image reject filter  92  or the output of GSM receive RF image reject filter  168  with a common receive RF LO  194 . 
     Common receive RF LO  194  is produced by coupling CDMA RF LO frequency source  70  and GSM RF LO frequency source  140  with a common receive RF LO power combiner  200 . The output of common receive RF LO power combiner  200  is approximately equivalent to either the output of CDMA RF LO frequency source  70  or the output of GSM RF LO frequency source  140 , because mode selector electronics  178  enables either CDMA RF LO frequency source  70  or GSM RF LO frequency source  140 , but not both. 
     The output of downconverter mixer  190  is coupled to CDMA receive IF filter  98  and GSM receive IF filter  176  through common receive IF power splitter  202 , which distributes a signal approximately equal in amplitude and phase to CDMA receive IF filter  98  and GSM receive IF filter  176 . In preferred embodiments, CDMA receive IF filter  98  and GSM receive IF filter  176  are surface acoustic wave (SAW) filters, because SAW filters act as high impedance elements for out-of-band frequencies. The outputs of CDMA receive IF filter  98  and GSM receive IF filter  176  are coupled to receive IF VGA  100  by first receive IF filter  206 . Because receive IF VGA  100  is shared between the CDMA-1900 and PCS receive paths, the gain, NF, and IIP 3  of receive IF VGA  100  must be chosen to satisfy the requirements of both the CDMA-1900 and PCS receive paths. 
     When mode selector electronics  178  is configured for CDMA operation, first receive RF switch  186  is configured to couple duplexer  82  to common receive RF LNA  184 , second receive RF switch  188  is configured to couple common receive RF LNA  184  to CDMA receive RF image reject filter  92 , and third receive RF switch  192  is configured to couple CDMA receive RF image reject filter  92  to common receive downconverter mixer  190 . When mode selector electronics  178  is configured for GSM operation, first receive RF switch  186  is configured to couple preselector filter  164  to common receive RF LNA  184 , second receive RF switch  188  is configured to couple common receive RF LNA  184  to GSM receive RF image reject filter  168 , and third receive RF switch  192  is configured to couple GSM receive RF image reject filter  168  to common receive downconverter mixer  190 . 
     It should also be noted that the RF filters in the GSM transmit and receive paths of CDMA-1900 and PCS communication transceiver  198  have different passbands as compared to those in FIG.  3 . GSM transmit RF filter  156  has a transmit passband encompassing the PCS transmit band of about 1850-1910 MHz, and preselector filter  164  and GSM receive RF image reject filter  168  have receive passbands approximately equivalent to the PCS receive band of about 1930-1990 MHz. 
     Furthermore, in alternative embodiments of the present invention wherein the DCS communication standard replaces the PCS communication standard in FIG. 6, GSM transmit RF filter  156  has a transmit passband encompassing the DCS transmit band of about 1710-1785 MHz, and preselector filter  164  and GSM receive RF image reject filter  168  have receive passbands approximately equivalent to the DCS receive band of about 1805-1880 MHz. 
     Although FIGS. 3-6 illustrate embodiments of the present invention which utilize modulation to, and demodulation from, an IF frequency, in alternative embodiments direct conversion may be employed. In direct conversion, receive RF information signals are downconverted and demodulated directly to baseband, and baseband information signals are modulated and upconverted directly to transmit RF information signals. 
     Therefore, according to the foregoing description, preferred embodiments of the present invention provide a system and process for a multi-mode, multi-band CDMA and GSM communication transceiver that shares frequency sources, amplifiers, and mixers between transmitters and receivers and between bands to minimize size, weight, complexity, power consumption, and cost. 
     The foregoing description of preferred embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.