Abstract:
A communication system for communicating RF signals at a plurality of communication standards through a common antenna is disclosed. The communication system includes a transmitter having transmitter outputs for generating transmit band signals in the transmit bands of each supported communication standard, and a receiver having receiver inputs for receiving receive band signals in the receive bands of each supported communication standard. The communication system also includes a plurality of RF switches. Each RF switch couples either the transmitter output or the receiver input associated with a particular communication standard to the antenna. Whether the communication unit is in transmit mode or receive mode, a harmonic filter coupled between each RF switch and the common antenna filters out harmonics of the transmit band and receive band signals. Each harmonic filter has a passband substantially encompassing the transmit and receive bands of the particular communication standard associated with the coupled RF switch.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates, generally, to communication systems, devices, and processes which use radio frequency (RF) transmitters and receivers, and, in particular embodiments, to such systems, processes, and devices which couple multi-band transmitters and receivers to a common antenna with minimal insertion loss, cost, and complexity.  
           [0003]    2. Description of Related Art  
           [0004]    It has become increasingly important to minimize the size, weight and power consumption 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. 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.  
           [0005]    For example, GSM900 (Global System for Mobile 900) is a digital cellular standard operating in the 900 MHz frequency band that is currently used in Europe and Asia. DCS 1800 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 1900, a third digital cellular standard similar to DCS 1800, but operating in the 1900 MHz band. Multi-band cellular telephones 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.  
           [0006]    Multi-band cellular telephones must be capable of transmitting and receiving different amplified and modulated transmit band signals through a common antenna. In addition, harmonics of the carrier frequencies must be filtered. To multiplex several different transmit band signals into a common antenna, some conventional multi-band cellular telephones use a resistor combiner, where first ends of individual resistors are coupled to the output of different transmit band generators, second ends of the individual resistors are coupled together, and another resistor is coupled between the second ends and an antenna. The resistor combiner allows simultaneous connection of multiple transmit band generators, and therefore does not require any control circuitry. However, resistor combiners may produce as much as 6 dB of loss, resulting in wasted power, and do not provide any filtering for harmonics of the carrier frequency.  
           [0007]    Another conventional approach uses an RF switch (for example, a GaAs or pin diode switch) controlled by a band select signal. In this approach, only one transmit band generator is connected to the antenna at any time. The RF switch approach has less loss than the resistor combiner, but it requires more expensive parts and the implementation of a band select control signal system. The RF switch approach also does not provide any filtering for harmonics of the carrier frequency.  
         SUMMARY OF THE DISCLOSURE  
         [0008]    Therefore, it is an object of embodiments of the present invention to provide a device, system and method for a communication unit that simultaneously couples multi-band transmitters and receivers to a common antenna with minimal insertion loss and wasted power relative to conventional systems, devices, and methods.  
           [0009]    It is a further object of embodiments of the present invention to provide a device, system and method for a communication unit that simultaneously couples multi-band transmitters and receivers to a common antenna and filters harmonics of the carrier frequencies.  
           [0010]    It is a further object of embodiments of the invention to provide a system, device, and method for a communication unit that simultaneously couples multi-band transmitters and receivers to a common antenna using minimal complexity and cost relative to conventional systems, devices, and methods.  
           [0011]    These and other objects are accomplished according to a communication system for communicating RF signals at a plurality of communication standards through a common antenna. Each communication standard has distinct transmit and receive bands. Examples of communication standards include the GSM, DCS, and PCS standards. The communication system includes a transmitter having transmitter outputs for generating transmit band signals in the transmit bands of each supported communication standard, and a receiver having receiver inputs for receiving receive band signals in the receive bands of each supported communication standard. The communication system also includes a plurality of RF switches. Each RF switch couples either the transmitter output or the receiver input associated with a particular communication standard to the antenna. Whether the communication unit is in transmit mode or receive mode, a harmonic filter coupled between each RF switch and the common antenna filters out harmonics of the transmit band and receive band signals. Each harmonic filter has a passband substantially encompassing the transmit and receive bands of the particular communication standard associated with the coupled RF switch.  
           [0012]    These and other objects, features, and advantages of embodiments of the 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  
       [0013]    [0013]FIG. 1 is block diagram representation of a system environment according to an example embodiment of the present invention.  
         [0014]    [0014]FIG. 2 is a more detailed block diagram representation of the modulator in the system of FIG. 1.  
         [0015]    [0015]FIG. 3 is a block diagram representation of dual band communication system according to an embodiment of the present invention.  
         [0016]    [0016]FIG. 4 is a schematic diagram of a GSM harmonic filter and a DCS/PCS harmonic filter according to an embodiment of the present invention.  
         [0017]    [0017]FIG. 5 is a plot of the frequency response of a GSM harmonic filter and a DCS/PCS harmonic filter according to an embodiment of the present invention.  
         [0018]    [0018]FIG. 6 is a block diagram representation of triple band communication system according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]    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.  
         [0020]    Cellular communication systems employ several different communication standards worldwide. 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. Embodiments of the present invention relate to systems, processes, and devices which couple multi-band cellular transmitters and receivers to a common antenna with minimal insertion loss and complexity.  
         [0021]    It should be noted that multi-band transmitters and receivers 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.  
         [0022]    Specifically, for purposes of illustration, the following discussion will focus on cellular communications and three communication standards, GSM900, DCS 1800, and PCS1900. In GSM900, frequency bands are allocated such that a mobile subscriber unit will transmit signals over a transmit band of between 890 and 915 MHz and will receive signals over a receive band of between 935 to 960 MHz. The transmit band is broken up into 125 channels, each channel separated by 200 kHz. In DCS1800, frequency bands are allocated such that a mobile subscriber unit will transmit signals over a transmit band of between 1710 and 1785 MHz and will receive signals over a receive band of between 1805 and 1880 MHz. The transmit band is broken up into 375 channels, each channel separated by 200 kHz. In PCS 1900, frequency bands are allocated such that a mobile subscriber unit will transmit signals over a transmit band of between 1850 and 1910 MHz and will receive signals over a receive band of between 1930 and 1990 MHz. The transmit band is broken up into 300 channels, each channel separated by 200 kHz. However, references to GSM, DCS, and PCS below are intended to refer generally to any set of different communication standards.  
         [0023]    A generalized representation of a communication system according to an embodiment of the present invention is shown in FIG. 1, wherein a communication system  10  includes a transmitting unit  12  and a receiving unit  14 , coupled for communication over a communication channel  42 . The transmitting unit  12  includes a modulator  16  connected to receive a data signal (baseband signal) from a signal source  18 . In one representative embodiment, the signal source  18  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  18  may include any suitable device for producing digital data signals for communication over the 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.  
         [0024]    The modulator  16  provides a modulated signal  32  as an output to a transmitter  20 . A transmit signal  26  is produced by the transmitter  20  for transmission from an antenna  22 . The receiving unit  14  includes a receiver  24  connected to an antenna  22  to process a receive signal  44 . The receiver  24  provides a modulated receive signal  34  to a demodulator  28  for demodulation to produce the data signal (baseband).  
         [0025]    The demodulated (baseband) signal output from the demodulator  28  may be provided to signal processing electronics, sound producing electronics or the like, depending upon the nature of use of the communication system. The transmitter and receiver units 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 system.  
         [0026]    In preferred two-way communication system 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, the transmitting unit  12  and receiving unit  14  transmit and receive signals directly therebetween. In other system embodiments, the transmitting unit  12  and receiving unit  14  communicate through one or more additional transmitter/receiver configurations (such as repeater, base or cell stations), generally represented as reference character  30  in FIG. 1.  
         [0027]    As illustrated in the modulator  16  of FIG. 2, in digital cellular telephone or cordless telephone system embodiments the signal source  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, the 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 filter  38  comprises a pulse shaping filter 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.  
         [0028]    I and Q outputs of the encoder pass through shaping filter  38  and then to the frequency conversion and modulation electronics  40 , the output of which comprises a modulated signal  32 . Modulated signal  32  is then fed to transmitter  20  as shown in FIG. 1, which provides the transmit signal  26  to the antenna  22  for transmission.  
         [0029]    A dual-band communication system  100  according to an embodiment of the present invention is illustrated in FIG. 3. For purposes of illustration and discussion, the dual-band communication system  100  of FIG. 3 is switchable between the GSM900 and DCS1800 communication standards. However, references to GSM and DCS are intended to refer generally to any two communication standards.  
         [0030]    Frequency conversion and modulation electronics  40  receive the I and Q outputs of the shaping filter  38  (see FIG. 2) and modulate an auxiliary synthesizer frequency  104  with the I and Q outputs to produce a modulated signal  32 . In preferred embodiments, auxiliary synthesizer frequency  104  is generated by an auxiliary frequency generator  150  containing an IF frequency generator  108  and auxiliary loop electronics  110  phase-locked to a reference source (not shown in FIG. 3). However, in alternative embodiments of the present invention, auxiliary frequency generator  150  may be any adjustable frequency source.  
         [0031]    A first filter  46  having a bandwidth sufficient to pass the modulated signal  32  with minimal distortion filters the modulated signal  32  before it enters an upconverter  48 . In preferred embodiments of the present invention, upconverter  48  includes two paralleled frequency generators, a GSM frequency generator  112  for generating GSM carrier frequencies and a DCS frequency generator  114  for generating DCS carrier frequencies. The outputs of GSM frequency generator  112  and DCS frequency generator  114  are selectively couplable to mixer  54  through an upconverter switch  116 , and are phase-locked to a main synthesizer frequency  56 . In preferred embodiments of the present invention, GSM frequency generator  112  and DCS frequency generator  114  are VCOs. In alternative embodiments of the present invention, upconverter switch  116  may be an RF switch, a resistor combiner, or a diplexer (two filters coupled together at their outputs).  
         [0032]    In preferred embodiments, mixer  54  generates the difference between the frequency at the output of upconverter switch  116  and main synthesizer frequency  56  generated by main frequency generator  152 . Main frequency generator  152  includes two paralleled frequency generators and main loop electronics  154  phase-locked to a reference source (not shown in FIG. 3). The two paralleled frequency generators include a main GSM frequency generator  144  for producing frequencies sufficient to generate desired GSM transmit or receive band frequencies, and a main DCS frequency generator  146  for producing frequencies sufficient to generate desired DCS transmit or receive band frequencies. The outputs of main GSM frequency generator  144  and main DCS frequency generator  146  are selectively couplable to mixer  54  and main loop electronics  154  through a main frequency generator switch  148 . In preferred embodiments of the present invention, main GSM frequency generator  144  and main DCS frequency generator  146  may be VCOs. In alternative embodiments of the present invention, main frequency generator switch  148  may be an RF switch, a resistor combiner, or a diplexer (two filters coupled together at their outputs). In other alternative embodiments, main frequency generator  152  may be any adjustable frequency source.  
         [0033]    Upconverter  48  further includes a feedback filter  60  for filtering the output of mixer  54 , a phase detector  62  for determining the phase difference between a filtered mixer output  64  and first filter output  50 , a charge pump  66  for sourcing or sinking current as determined by the phase difference output of phase detector  62 , and a loop filter  68  for integrating current pulses from charge pump  66  and providing a control voltage  70  to GSM frequency generator  112  and DCS frequency generator  114 . In other alternative embodiments, upconverter  48  may comprise a mixer for mixing first filter output  50  with main synthesizer frequency  56 .  
         [0034]    A GSM power amplifier  120  controllable by a power amplifier controller  118  is coupled between GSM frequency generator  112  and a GSM T/R switch  76  to generate a GSM transmit signal  156 . Similarly, a DCS power amplifier  124  controllable by power amplifier controller  118  is coupled between DCS frequency generator  114  and a DCS T/R switch  176  to generate a DCS transmit signal  158 . Power amplifier controller  118  receives baseband control signals (not shown in FIG. 3), senses the output power of GSM power amplifier  120  and DCS power amplifier  124 , and adjusts the amplification of GSM power amplifier  120  and DCS power amplifier  124  based on these inputs and a predetermined ramping profile. A GSM harmonic filter  122  is coupled between GSM T/R switch  76  and antenna  22  to pass GSM transmit band frequencies and suppress harmonics of GSM transmit signal  156  generated by GSM power amplifier  120 . A DCS harmonic filter  126  is coupled between DCS T/R switch  176  and antenna  22  to pass DCS transmit band frequencies and suppress harmonics of DCS transmit signal  158  generated by DCS power amplifier  124 . Thus, GSM harmonic filter  122  and DCS harmonic filter  126  are simultaneously coupled to antenna  22 .  
         [0035]    Upconverter switch  116 , main frequency generator switch  148 , main loop electronics  154 , auxiliary loop electronics  110 , and power amplifier controller  118  are all coupled to and controllable by band selector  106 . When band selector  106  is configured for GSM operation, upconverter switch  116  selects GSM frequency generator  112 , main frequency generator switch  148  selects main GSM frequency generator  144 , and power amplifier controller  118  enables GSM power amplifier  120  and disables DCS power amplifier  124 . When band selector  106  is configured for DCS operation, upconverter switch  116  selects DCS frequency generator  114 , main frequency generator switch  148  selects main DCS frequency generator  146 , and power amplifier controller  118  enables DCS power amplifier  124  and disables GSM power amplifier  120 .  
         [0036]    Auxiliary loop electronics  110  and main loop electronics  154  are also controllable by transmit/receive selector circuit  160 . When band selector  106  is configured for GSM operation and transmit/receive selector circuit  160  is configured for transmit operation, auxiliary loop electronics  110  configures its dividers and frequency source (not shown in FIG. 3) in accordance with a designated GSM transmit IF, and main loop electronics  154  configures its dividers and frequency source (not shown in FIG. 3) in accordance with a designated GSM transmit band. When band selector  106  is configured for GSM operation and transmit/receive selector circuit  160  is configured for receive operation, auxiliary loop electronics  110  configures its dividers and frequency source in accordance with a designated GSM receive IF, and main loop electronics  154  configures its dividers and frequency source in accordance with a designated GSM receive band. When band selector  106  is configured for DCS operation and transmit/receive selector circuit  160  is configured for transmit operation, auxiliary loop electronics  110  configures its dividers and frequency source in accordance with a designated DCS transmit IF, and main loop electronics  154  configures its dividers and frequency source in accordance with a designated DCS transmit band. When band selector  106  is configured for DCS operation and transmit/receive selector circuit  160  is configured for receive operation, auxiliary loop electronics  110  configures its dividers and frequency source in accordance with a designated DCS receive IF, and main loop electronics  154  configures its dividers and frequency source in accordance with a designated DCS receive band.  
         [0037]    When GSM T/R switch  76  and DCS T/R switch  176  are switched to receiver  24  for operating communication system  10  in receive mode, GSM harmonic filter  122  passes GSM receive band frequencies to GSM receive filter  142 , and DCS harmonic filter  126  passes DCS receive band frequencies to DCS receive filter  140 . If band selector  106  is configured for GSM operation, an adjustable gain DCS downconverter amplifier  166  is disabled, while an adjustable gain GSM downconverter amplifier  162  senses the power level of received baseband signals and amplifies the output of GSM receive filter  142  accordingly. If band selector  106  is configured for DCS operation, the adjustable gain GSM downconverter amplifier  162  is disabled, while the adjustable gain DCS downconverter amplifier  166  senses the power level of received baseband signals and amplifies the output of DCS receive filter  140  accordingly. The amplified signal is then translated into a downconverted receive signal  88  by a downconverter  164  utilizing a main synthesizer frequency  56  from main frequency generator  152 .  
         [0038]    Downconverted receive signal  88  is then filtered by a first downconverted receive filter  90  to remove spurious frequencies generated by downconverter  164 , amplified by an adjustable first downconverter amplifier  92  which senses the power level of received baseband signals and amplifies the output of downconverter receive filter  90  accordingly, and filtered again by a second downconverted receive filter  94  to reject noise generated by the first downconverter amplifier  92 . The filtered signal then enters demodulator  28 , where the signal is demodulated into baseband I and Q channel signals using an auxiliary synthesizer frequency  104  from auxiliary frequency generator  150 .  
         [0039]    [0039]FIG. 4 is a circuit representation of GSM harmonic filter  122  and DCS harmonic filter  126  according to an embodiment of the present invention. GSM harmonic filter  122  uses low-pass filter (LPF) topology comprised of a LPF capacitor  128  coupled between a first LPF inductor  130  and a second LPF inductor  132 , both inductors also connected to ground. DCS harmonic filter  126  uses high-pass filter (HPF) topology comprised of a HPF inductor  134  coupled between a first HPF capacitor  136  and a second HPF capacitor  138 , both capacitors also connected to ground. It should be noted that the embodiment of FIG. 4 utilizes inexpensive components and produces very little insertion loss.  
         [0040]    In embodiments of the present invention for the dual-band communication system  100  under discussion, component values should be chosen such that the GSM harmonic filter  122  passes frequencies in the GSM transmit band (890-915 MHz) and GSM receive band (935-960 MHz) but rejects harmonics of the GSM carrier frequency. Component values should also be chosen such that the DCS harmonic filter  126  passes frequencies in the DCS transmit band (1710-1785 MHz) and DCS receive band (1805-1880 MHz) but rejects harmonics of the DCS carrier frequency.  
         [0041]    Although GSM harmonic filter  122  and DCS harmonic filter  126  utilize LPF and HPF topologies, respectively, when coupled together as in FIG. 4 the filters are mutually affected and exhibit bandpass characteristics. Thus, the design of the two filters must be conducted simultaneously. In preferred embodiments of the present invention for the dual-band communication system  100  under discussion, selecting the LPF capacitor  128  to be approximately 6.2 pF, the first LPF inductor  130  to be approximately 1.4 nH, the second LPF inductor  132  to be approximately 1.0 nH, the HPF inductor  134  to be approximately 2.6 nH, the first HPF capacitor  136  to be approximately 4.6 pF, and the second HPF capacitor  138  to be approximately 12.0 pF will result in the frequency response of FIG. 5. Reference character  122  corresponds to the frequency response of GSM harmonic filter  122 , and reference character  126  corresponds to the frequency response of DCS harmonic filter  126 . Frequency response  122  in FIG. 5 corresponds to a filter which passes GSM transmit and receive frequencies, while frequency response  126  corresponds to a filter which passes DCS and PCS transmit and receive frequencies.  
         [0042]    A triple-band communication system  200  according to a preferred embodiment of the present invention is illustrated in FIG. 6. For purposes of illustration and discussion, triple-band communication system  200  of FIG. 6 is switchable between the GSM900, DCS1800, and PCS1900 communication standards. However, references to GSM, DCS, and PCS are intended to refer generally to any three communication standards. In alternative embodiments, triple band communication system  200  may be expanded to include any number of different bands.  
         [0043]    The structure and operation of triple-band communication system  200  is similar to that of dual-band communication system  100  of FIG. 3, except for those differences noted below. In the triple-band communication system  200  of FIG. 6, upconverter  48  includes a third paralleled frequency generator, a PCS frequency generator  168  for generating PCS carrier frequencies. The outputs of PCS frequency generator  168  and DCS frequency generator  114  are selectively couplable to DCS power amplifier  124  through a DCS/PCS switch  170 , controllable by band selector  106 . Main frequency generator  152  includes a third paralleled frequency generator, a tunable main PCS frequency generator  172  for generating PCS transmit or receive band frequencies. The output of main PCS frequency generator  172  is selectively couplable to mixer  54  and main loop electronics  154  though main frequency generator switch  148 .  
         [0044]    Because the frequency response of DCS harmonic filter  126  passes both DCS and PCS transmit and receive frequencies, in preferred embodiments of the present invention DCS harmonic filter  126  can be used to transmit and receive both DCS and PCS channels, as illustrated in FIG. 6. Thus, DCS harmonic filter  126  passes PCS receive band frequencies as well as DCS receive band frequencies to DCS receive filter  140  and a PCS receive filter  174 . The outputs of DCS receive filter  140  and PCS receive filter  174  are coupled together, as shown in FIG. 6. Because triple-band communication system  200  will receive either DCS or PCS receive band frequencies at any time, but not both, the coupled outputs of DCS receive filter  140  and PCS receive filter  174  present no mixing problem.  
         [0045]    Therefore, according to the foregoing description, preferred embodiments of the present invention provide a device, system and method for a communication unit that simultaneously couples multi-band transmitters and receivers to a common antenna with minimal insertion loss and wasted power, and filters harmonics of transmit band carrier frequencies using minimal complexity and cost.  
         [0046]    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.