Patent Publication Number: US-2011051868-A1

Title: Various impedance fm receiver

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
     NOT APPLICABLE 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC  
     NOT APPLICABLE 
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     This invention is related generally to frequency modulated (FM) systems, and more particularly to FM receiver architectures. 
     2. Description of Related Art 
     Conventional broadcast radio stations operate on fixed radio frequency (RF) channels. In the U.S., these channels are regulated and licensed for specific purposes by the Federal Communications Commission (FCC). For example, the frequency band from 535 kilohertz (kHz) to 1.7 megahertz (MHz) is designated for AM broadcast radio, while the frequency band from 88 MHz to 108 MHz is designated for FM broadcast radio. Within any particular region of the U.S., there may be one or more radio stations broadcasting within the FM frequency band. The FCC designates a particular FM radio channel to each radio station, so that no two radio stations are broadcasting on the same radio channel within the same region. 
     To tune a radio device to a particular broadcasting radio station, either a user can select the desired radio channel on the radio device or the radio device can scan through the FM frequency band until the desired radio channel is reached. Increasingly, FM radio devices are being incorporated into hand-held wireless devices, such as cell phones, personal audio/visual (A/V) players, personal digital assistants (PDAs) and other similar devices, to enable users to listen to broadcast radio on their wireless device. 
     In addition, outside of the broadcast spectrum, FM radio devices are being used within two-way radio devices to search for FM channels with a valid transmission. To avoid interference with nearby FM radio stations, the radio devices communicate on FM radio channels that are inactive in the region that the radio devices are located. That is, the radio devices communicate using FM radio channels that are not allocated to any radio station within the area and on which no signal is currently present. 
     Once communication between the radio devices is established over an inactive FM radio channel, the radio devices may communicate audio data (e.g., speech or music) and/or digital data, such as numeric messages and/or text messages, over the FM radio channel. In addition, the radio devices may employ modulation schemes, such as frequency shift keying, audio frequency shift keying or quadrature shift keying to encode the data. Therefore, each FM radio device typically includes a built-in transceiver (transmitter and receiver) for modulating/demodulating information (data or speech) bits into a format that comports with a particular communication standard utilized by the radio devices. 
     When the FM radio device is incorporated into another wireless device, such as a cell phone, the transceiver can be shared between FM and traditional cellular operations. Therefore, a traditional cell phone antenna, i.e., a 50 ohm antenna, typically provides both cellular and FM reception. However, using a 50 ohm antenna requires FM transceivers to be operated at high power. As a result, FM transceivers often suffer from a shortened battery life. Therefore, manufacturers and users of FM transceivers may want to utilize different types of antennas in the transmit and/or receive paths. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to apparatus and methods of operation that are further described in the following Brief Description of the Drawings, the Detailed Description of the Invention, and the claims. Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  is a schematic block diagram illustrating a communication system that includes FM radio devices capable of communicating with each other using frequencies within the FM radio spectrum in accordance with the present invention; 
         FIG. 2  is a schematic block diagram illustrating a wireless device that includes a host device and an associated FM radio in accordance with the present invention; 
         FIG. 3  is a schematic block diagram illustrating an FM radio receiver in accordance with the present invention; 
         FIG. 4  is a schematic block diagram illustrating the FM radio receiver including variable gain stages in accordance with the present invention; 
         FIGS. 5-7  are schematic block diagrams illustrating more detailed views of a wireless device including an FM radio receiver in accordance with the present invention; 
         FIG. 8  is a circuit diagram illustrating an exemplary low noise amplifier for use within the FM radio receiver in accordance with the present invention; 
         FIG. 9  is a logic diagram of a method for operating a wireless device including an FM radio receiver in accordance with the present invention; and 
         FIG. 10  is a logic diagram of a method for configuring an FM radio receiver, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a functional block diagram illustrating an exemplary wireless system  10  for use in embodiments of the present invention. The wireless system shown in  FIG. 1  includes a plurality of wireless devices  18 - 28 . For example, the wireless devices may be radio devices, such as FM radio devices  26  and  28 , or communication devices, such as laptop computer  18 , personal digital assistant  20 , cellular telephone  22  and/or personal computer  24 . FM radio devices  26  and  28  may be car radios, portable radios, personal A/V players, such as MP3 players, and/or other wireless devices that include FM radio devices. 
     Currently, there is a trend towards enabling cellular telephone  22  and other wireless devices, such as laptop computers  18 , PDAs  20 , personal computers  24  and other devices  26  and  28  (e.g., MP3 players, portable radios, etc.), to provide FM transmission and/or reception. Therefore, in  FIG. 1 , each of the wireless devices  18 - 28  may include an FM transmitter operable to transmit a frequency modulated (FM) signal within the FM frequency band on one or more FM radio frequencies. In addition, each of the wireless devices  18 - 28  may further include an FM receiver operable to receive an FM signal within the FM frequency band on one or more FM radio frequencies. As used herein, the term “FM frequency band” includes frequencies between 65 MegaHertz (MHz) and 108 MHz. 
     For example, in the U.S., FM radio stations are allocated respective FM channels, each containing 200 kHz of bandwidth around the carrier frequency (in Europe, it is 100 kHz). To listen to broadcast radio on the wireless devices, each of the wireless devices  18 - 28  includes an FM receiver operable to tune to a particular FM channel and receive a radio frequency (RF) signal within the FM frequency band on the selected FM radio channel. 
     In addition, to enable two-way radio communication over FM channels, each of the wireless devices  18 - 28  further includes an FM transmitter. To avoid interference with nearby FM radio stations, the wireless devices  18 - 28  communicate on FM radio channels that are inactive in the region that the wireless devices  18 - 28  are located. That is, the wireless devices  18 - 28  communicate using FM radio channels that are not allocated to any radio station within the area and on which no signal is currently present. 
     Once communication between the wireless devices is established over an inactive FM radio channel, the wireless devices may communicate audio data (e.g., speech and/or music) and/or digital data, such as numeric messages and/or text messages, over the FM radio channel. In addition, the wireless devices  18 - 28  may employ modulation schemes, such as frequency shift keying, audio frequency shift keying or quadrature shift keying to encode the data transmitted via the selected inactive FM channel. For example, if a received FM radio signal includes digital data, the wireless device  18 - 28  receiving the FM radio signal can demodulate the digital data, and then display the digital data on a display of the wireless device  18 - 28 . 
     Furthermore, each of the communication devices  18 - 24  includes a transceiver (transmitter and receiver) for communicating with a base station or access point  12 - 14  of a wireless communication network. In one embodiment, the communication devices  18 - 24  include separate transceivers for FM and cellular communications. In another embodiment, the communication devices  18 - 24  include a single transceiver capable of supporting both FM and cellular operations. 
     Typically, base stations are used for cellular telephone networks and like-type networks, while access points are used for in-home or in-building wireless networks. For example, access points are typically used in Bluetooth systems. Regardless of the particular type of wireless communication network, the communication devices  18 - 24  and the base station or access point  12 - 14  each include a built-in transceiver (transmitter and receiver) for modulating/demodulating information (data or speech) bits into a format that comports with the type of wireless communication network. There are a number of well-defined wireless communication standards (e.g., IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof) that could facilitate such wireless communication between the communication devices  18 - 24  and a wireless communication network. 
     The base stations or access points  12 - 14  are coupled to a network hardware component  30  via local area network (LAN) connections  36  and  38 . The network hardware component  34 , which may be a router, switch, bridge, modem, system controller, etc., provides a wide area network (WAN) connection  40  for the wireless communication network. Each of the base stations or access points  12 - 14  has an associated antenna or antenna array to communicate with the wireless communication devices in its area. Typically, the wireless communication devices  18 - 24  register with the particular base station or access points  12  or  14  to receive services from the wireless network. For direct connections (i.e., point-to-point communications), wireless communication devices communicate directly via an allocated channel. Although a network topology is shown in  FIG. 1 , it should be understood that the present invention is not limited to network topologies, and may be used in other environments, such as peer-to-peer, access point or mesh environments. 
       FIG. 2  is a schematic block diagram illustrating a wireless device that includes the host device  18 - 28  and an associated radio  60 , which can be an FM radio, a cellular radio or a combined FM/cellular radio. For cellular telephone hosts and radio hosts, the radio  60  is a built-in component. For personal digital assistants hosts, laptop hosts, and/or personal computer hosts, the radio  60  may be built-in or an externally coupled component. 
     As illustrated, the host device  18 - 28  includes a processing module  50 , memory  52 , a radio interface  54 , an input interface  58  and an output interface  56 . The processing module  50  and memory  52  execute the corresponding instructions that are typically done by the host device  18 - 28 . For example, for a cellular telephone host device, the processing module  50  performs the corresponding communication functions in accordance with a particular cellular telephone standard. 
     The radio interface  54  allows data to be received from and/or sent to the radio  60 . For data received from the radio  60  (e.g., inbound data), the radio interface  54  provides the data to the processing module  50  for further processing and/or routing to the output interface  56 . The output interface  56  provides connectivity to an output device such as a display, monitor, speakers, etc., such that the received data may be displayed. The radio interface  54  also provides data from the processing module  50  to the radio  60 . The processing module  50  may receive the outbound data from an input device, such as a keyboard, keypad, microphone, etc., via the input interface  58  or generate the data itself. For data received via the input interface  58 , the processing module  50  may perform a corresponding host function on the data and/or route it to the radio  60  via the radio interface  54 . 
     Radio  60  includes a host interface  62 , a transmitter  102 , a memory  75 , a local oscillation module  74 , and in embodiments in which the radio  60  is a transceiver, a receiver  100  and an optional transmitter/receiver (Tx/Rx) switch module  73 . The radio  60  further includes an antenna  86 . In the transceiver shown in  FIG. 2 , the antenna  86  is shared by the transmit and receive paths as regulated by the Tx/Rx switch module  73 . However, in other embodiments, the transmit and receive paths may use separate antennas or multiple antennas can be coupled to the Tx/Rx switch module  73  to switch between different antennas for the transmit and receive paths. In addition, in embodiments in which the host device  18 - 28  is a communication device, such as a cell phone, laptop computer, personal computer or PDA, the radio  60  and antenna  86  may be shared between cellular and FM applications. For example, the local oscillation module  74  may be configured to provide an appropriate local oscillation signal for up-converting and down-converting both FM and cellular frequencies, depending on the mode of operation (FM or cellular). In other embodiments, a separate antenna  86  and/or radio  60  may be provided for cellular and FM applications. 
     As shown in  FIG. 2 , the receiver  100  includes a digital receiver processing module  64 , an analog-to-digital converter  66 , a filtering/gain module  68 , a down-conversion module  70 , a low noise amplifier  72  and a receiver filter module  71 . The transmitter  102  includes a digital transmitter processing module  76 , a digital-to-analog converter  78 , a filtering/gain module  80 , an IF mixing up-conversion module  82 , a power amplifier  84  and a transmitter filter module  85 . 
     The digital receiver processing module  64  and the digital transmitter processing module  76 , in combination with operational instructions stored in memory  75 , execute digital receiver functions and digital transmitter functions, respectively. The digital receiver functions include, but are not limited to, demodulation, constellation demapping, decoding, and/or descrambling. The digital transmitter functions include, but are not limited to, scrambling, encoding, constellation mapping, and/or modulation. The digital receiver and transmitter processing modules  64  and  76 , respectively, may be implemented using a shared processing device, individual processing devices, or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. 
     Memory  75  may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the digital receiver processing module  64  and/or the digital transmitter processing module  76  implements one or more of its functions via analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the analog circuitry, digital circuitry, and/or logic circuitry. Memory  75  stores, and the digital receiver processing module  64  and/or the digital transmitter processing module  76  executes, operational instructions corresponding to at least some of the functions illustrated herein. 
     In an exemplary operation of the receiver  100 , when the radio  60  receives an inbound radio frequency (RF) signal  88  having a particular bandwidth and carrier frequency tuned to by the antenna  86 , which was transmitted by another wireless device, the antenna  86  provides the inbound RF signal  88  to the receiver filter module  71  via the Tx/Rx switch module  73 . The Rx filter module  71  bandpass filters the inbound RF signal  88  and provides the filtered RF signal to low noise amplifier  72 , which amplifies the inbound RF signal  88  to produce an amplified inbound RF signal. The low noise amplifier  72  provides the amplified inbound RF signal to the down-conversion module  70 , which directly converts the amplified inbound RF signal into an inbound low IF signal (e.g., at 200 kHz IF) based on a receiver local oscillation  81  provided by local oscillation module  74 . The down-conversion module  70  provides the inbound low IF signal to the filtering/gain module  68 . 
     The analog-to-digital converter  66  converts the filtered inbound signal from the analog domain to the digital domain to produce digital reception formatted data  90 . The digital receiver processing module  64  decodes, descrambles, demaps, and/or demodulates the digital reception formatted data  90  to recapture inbound data  92 . The host interface  62  provides the recaptured inbound data  92  to the host device  18 - 32  via the radio interface  54 . 
     In an exemplary operation of the transmitter  102 , when the radio  60  receives outbound data  94  from the host device  18 - 28  via the host interface  62 , the host interface  62  routes the outbound data  94  to the digital transmitter processing module  76 . The digital transmitter processing module  76  processes the outbound data  94  in accordance with a particular wireless communication standard (e.g., IEEE 802.11a, IEEE 802.11b, Bluetooth, etc.), if necessary, to produce digital transmission formatted data  96 . The digital-to-analog converter  78  converts the digital transmission formatted data  96  from the digital domain to the analog domain. The filtering/gain module  80  filters and/or adjusts the gain of the analog low IF signal prior to providing it to the up-conversion module  82 . The up-conversion module  82  directly converts the analog low IF signal into an RF signal based on a transmitter local oscillation  83  provided by local oscillation module  74 . The power amplifier  84  amplifies the RF signal to produce an outbound RF signal  98 , which is filtered by the transmitter filter module  85 . The antenna  86  transmits the outbound RF signal  98  to a targeted device, such as another wireless device. 
     As one of average skill in the art will appreciate, the wireless device of  FIG. 2  may be implemented using one or more integrated circuits. For example, the host device  18 - 28  may be implemented on a first integrated circuit, while the digital receiver processing module  64 , memory  75  and/or the digital transmitter processing module  76  may be implemented on a second integrated circuit, and the remaining components of the radio  60 , less the antenna  86 , may be implemented on a third integrated circuit. As an alternate example, the radio  60  may be implemented on a single integrated circuit. As yet another example, the processing module  50  of the host device  18 - 28  and the digital receiver processing module  64  and/or the digital transmitter processing module  76  may be a common processing device implemented on a single integrated circuit. Further, memory  52  and memory  75  may be implemented on a single integrated circuit and/or on the same integrated circuit as the common processing modules of processing module  50 , the digital receiver processing module  64 , and/or the digital transmitter processing module  76 . 
       FIG. 3  is a schematic block diagram illustrating an FM radio receiver  110  in accordance with the present invention. The FM radio receiver  110  corresponds, at least in part, to the receiver  100  shown in  FIG. 2 . The FM radio receiver  110  of  FIG. 3  provides a flexible architecture to enable different types of antennas with different impedances to be coupled to the FM receiver  110 . 
     The FM radio receiver in  FIG. 3  includes antennas  112  and  114 , antenna pins  116 / 118 , switch  120 , low noise amplifiers  122  and  124 , an optional gain stage (Gm)  126 , a mixer  128 , a low pass filter (LPF)  130 , analog-to-digital converter (ADC)  132  and digital baseband processor  134 , which correspond, at least in part, to the functionality of blocks  64 - 73  and  86  of  FIG. 2 . The processor  134  may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. 
     The antennas  112  and  114  can each be a different type of antenna and/or have different impedances. For example, antenna  112  can be a cell phone antenna with an impedance of 50 Ω (ohms), while antenna  114  can be a loop antenna with an impedance of 2 kΩ. As another example, one of the antennas could be a small form factor (SFF) antenna or any other type of antenna. 
     To enable different antennas with different impedances to be coupled to the receiver  110 , each of the LNAs  122 / 124  has a programmable impedance, as described in more detail below in connection with  FIGS. 5-8 , in order to provide either antenna impedance matching or no matching (for low impedance antennas). The LNA  122 / 124  impedance can be set off-line during manufacture of the wireless device incorporating the FM receiver  110  and/or in real-time, for example, in response to a new antenna being coupled to the FM receiver  110  by a user. 
     Once the LNA impedances have been set based on the types of antennas  112 / 114  inserted into antenna pins  116 / 118 , switch  120  selectively couples antenna  112  to LNA  122  and antenna  114  to LNA  124 . For example, switch  120  can couple only antenna  112  to LNA  122 , only antenna  114  to LNA  124  or both antenna  112  to LNA  122  and antenna  114  to LNA  124 . In one embodiment, switch  120  operates to selectively physically couple antenna  112  to LNA  122  and to selectively physically couple antenna  114  to LNA  124 . In another embodiment, switch  120  functions as a power control module to selectively provide power to LNA  122  and/or LNA  124 , and therefore, effectively selectively couple LNAs  122 / 124  to antennas  112 / 114 . In addition, although two LNA&#39;s  122  and  124  are shown, in other embodiments, only a single LNA (e.g., LNA  122 ) may be used and the switch  120  operates to couple one of the antennas  112 / 114  to the single LNA  122 . 
     The switch  120  can further operate as the Tx/Rx switch module shown in  FIG. 2  if only one of the antennas  112 / 114  is used for both transmit and receive operations. For example, antenna pin  116  can be an Rx (receiver) antenna pin, while antenna pin  118  can be a Tx (transmitter) antenna pin. Switch  120  can enable the receiver  110  to utilize the Tx antenna  114  while in a receive mode and the transmitter (not shown) to utilize the Tx antenna  114  while in a transmit mode. In addition, simultaneous transmit/receive operations may be possible. For example, when the transmitter is operating in a cellular mode via antenna  114 , the receiver  110  may be able to simultaneously receive an FM signal via antenna  112  or antenna  114 . 
     In an exemplary operation, switch  120  couples antenna  114  to LNA  124  to enable an inbound radio frequency (RF) signal received at antenna  114  to be provided to LNA  124 . LNA  124  amplifies the inbound RF signal to produce an amplified inbound RF signal. The LNA  124  provides the amplified inbound RF signal to the mixer  128  via the optional gain stage  126 . The mixer  128  converts the amplified inbound RF signal into an inbound low IF or near baseband signal (e.g., at 200 kHz IF). The mixer  128  provides the inbound near baseband signal to the LPF  130 , which filters the near baseband signal to produce a filtered baseband signal. The ADC  132  converts the filtered baseband signal from the analog domain to the digital domain to produce a digital baseband signal and provides the digital baseband signal to the processor  134 . The processor  134  decodes, descrambles, demaps, and/or demodulates the digital baseband signal to recapture inbound data (i.e., inbound digital symbols). 
     In another exemplary operation, switch  120  couples antenna  112  to LNA  122  to enable an inbound radio frequency (RF) signal received at antenna  112  to be provided to LNA  122 . LNA  122  amplifies the inbound RF signal to produce an amplified inbound RF signal. The LNA  122  provides the amplified inbound RF signal to the mixer  128  via the optional gain stage  126 . The mixer  128  converts the amplified inbound RF signal into an inbound low IF or near baseband signal (e.g., at 200 kHz IF). The mixer  128  provides the inbound near baseband signal to the LPF  130 , which filters the near baseband signal to produce a filtered baseband signal. The ADC  132  converts the filtered baseband signal from the analog domain to the digital domain to produce a digital baseband signal and provides the digital baseband signal to the processor  134 . The processor  134  processes the digital baseband signal to recapture inbound data (i.e., inbound digital symbols). 
     In yet another exemplary operation, switch  120  couples antenna  112  to LNA  122  and couples antenna  114  to LNA  124  to enable respective inbound radio frequency (RF) signals received at antennas  112  and  114  to be provided to LNAs  122  and  124 . LNAs  122  and  124  each amplify the respective inbound RF signal to produce respective amplified inbound RF signals. The outputs of LNAs  122  and  124  are combined to produce a combined amplified inbound RF signal that is input to the mixer  128  via the optional gain stage  126 . The mixer  128  converts the combined amplified inbound RF signal into an inbound low IF or near baseband signal (e.g., at 200 kHz IF). The mixer  128  provides the inbound near baseband signal to the LPF  130 , which filters the near baseband signal to produce a filtered baseband signal. The ADC  132  converts the filtered baseband signal from the analog domain to the digital domain to produce a digital baseband signal and provides the digital baseband signal to the processor  134 . The processor  134  processes the digital baseband signal to recapture inbound data (i.e., inbound digital symbols). 
     Each antenna pin  116  and  118  can also include an antenna detector circuit that transmits a signal to the digital baseband processor  134  whenever an antenna is inserted into the antenna pin  116 / 118 . The processor  134  may control the selective coupling of one or both of the antennas  112 / 114  to the receiver based upon the detection signal. For example, in an exemplary operation, at least one of antenna detector circuits  116 / 118  detects the presence of an antenna  112 / 114  and transmits a signal  136  indicative of the antenna presence to the processor  134 . In response, the processor  134  sends a signal  135  to the switch  120  to couple one or both antennas  112 / 114  to LNAs  122 / 124  based on pre-defined criteria. 
     In one embodiment, the pre-defined criteria can indicate that if an antenna  112  is coupled to the receiver pin  116 , the receiver antenna  112  is coupled to the LNA  122 , and any antenna  114  present on the transmitter pin  118  is not connected to LNA  124 . In another embodiment, the pre-defined criteria can couple both antennas  112 / 114  to their respective LNAs  122 / 124  in order to boost the signal in the receiver  110 . 
     The antenna detector circuits may further be able to measure the impedance of the antennas to determine the type of antennas  116 / 118  inserted into the pins  116 / 118  to enable automatic configuration of the LNA impedance to match the antenna impedance. For example, the processor  134  can transmit a signal to the LNA&#39;s  122 / 124  to set the respective impedances thereof based on the measured impedance of the antennas  112 / 114  inserted into antenna pins  116 / 118 . In addition, the pre-defined criteria can instruct the processor  134  to couple the antenna  112 / 114  with the highest impedance to its respective LNA  122 / 124  in order to operate the receiver  110  at a lower power, as will be described in more detail below in connection with  FIG. 4 . 
       FIG. 4  is a schematic block diagram illustrating the FM radio receiver  110  including variable gain stages in accordance with the present invention. Each of the gain stages FM receiver  110  (e.g., the LNAs  122 / 124 , Gm  126 , mixer  128 , LPF  130  and ADC  132 ) are substantially linear in order to minimize out of band spurious transmissions. In addition, by maintaining a constant voltage, a high Q, high impedance antenna  112 / 114  (e.g., greater than 2 kΩ with a Q of 30 in the FM frequency band and an inductance of at least 120 nanohenry) may be used. As such, the FM receiver  110  can be operated at a much lower power than when a traditional 50 Ω antenna is used. 
     To maintain a constant voltage, in one embodiment, the FM radio receiver  110  in  FIG. 4  includes a receiver signal strength indicator (RSSI)  138  coupled to the output of the various gain stages (LNAs  122 / 124 , Gm  126 , mixer  128 , LPF  130  and ADC  132 ). The RSSI  138  measures the output power at the output of the various gain stages and generates a power control signal (RSSI_Out)  140  indicative of the output power. The power control signal  140  is input to the digital baseband processor  134 , which uses the power control signal  140  to generate gain control signal(s)  142 ,  144 ,  145 ,  146  and  148  o control the gains of the ADC  132 , LPF  130 , Gm  126  and LNAs  122 / 124 , respectively, in order to maintain a constant transmit voltage. 
     For example, the digital baseband processor  134  can compare the measured output power of each gain stage to a desired output power thereof to determine a power offset therebetween. The digital baseband processor  134  can then calculate the respective gains of the ADC  132 , LPF  130 , Gm  126  and LNAs  122 / 124  that are needed in order to minimize the power offset, and therefore, bring the measured output power substantially equal to the desired output power. Once the gains have been calculated, the digital baseband processor can generate and transmit a gain control signal (ADC_CTL)  142  to the ADC  132  to set the gain of the ADC  132 , a gain control signal (LPF_CTL)  144  to the LPF  130  to set the gain of the LPF  130 , a gain control signal (MIXER_CTL)  145  to set the gain of the mixer  128 , a gain control signal (Gm_CTL)  146  to the Gm  126  to set the gain of the Gm  126  and a gain control signal (LNA_CTL)  148  to the LNAs  122 / 124  to set the gain of the LNAa  122 / 124 . 
     This process can be repeated recursively until the power offset between the measured and desired output power is sufficiently minimized or eliminated. In an exemplary embodiment, this process is performed during an off-line calibration operation of the FM receiver  110  and/or during a real-time, on-line, change channel operation of the FM receiver  110 . 
       FIGS. 5-7  are schematic block diagrams illustrating more detailed views of an FM radio receiver  200  in accordance with the present invention. For example, as shown in  FIG. 5 , the FM radio receiver  200  includes LNAs  212  and  214 , gain stages (Gm)  216  and  218  and a mixer  220 . Each of the LNA&#39;s  212  and  214  is coupled via a respective input pad  208  and  210  to a receiver antenna  202  via an optional filter  204  and balun  206 . In addition, the FM receiver  200  further includes additional LNA&#39;s  230  and  232 , coupled via input pad  228  to a transmitter antenna  226 . The additional LNAs  230  and  232  may be coupled to the transmitter antenna  226  via a Tx/Rx switch module, as shown in  FIG. 2 . For example, a Tx/Rx switch module can couple the transmitter antenna  226  to either LNAs  230 / 232  or to a power amplifier (PA)  234  of the transmitter (Tx). As such, the LNas  230 / 232  may be positioned within the transmitter and coupled to the receiver  200 . 
     The components shown in  FIGS. 5-7  correspond, at least in part, to the functionality of blocks  112 - 128  of  FIG. 3 . For example, LNAs  212  and  214  can correspond to LNA  122 , while LNAs  230  and  232  can correspond to LNA  124 . In addition, gain stages  216  and  218  can correspond to gain stage  126  and mixer  220  can correspond to mixer  128 . 
     Each of  FIGS. 5-7  illustrates the FM receiver  200  operating in a different mode. For example,  FIGS. 5  illustrates an FM receiver  200  operating in a differential mode with antenna matching impedance,  FIG. 6  illustrates the FM receiver  200  operating in a single ended mode with antenna matching impedance and  FIG. 7  illustrates the FM receiver  200  operating in a single ended mode with no antenna matching impedance. 
     Turning now to  FIG. 5 , when the FM receiver  200  is operating in differential mode, the radio frequency (RF) signal at the input to the receiver  200  is a complex signal that includes an in-phase component (I) and a quadrature component (Q). To generate the I and Q signals, the balun  206 , which is shown in  FIG. 5  as including two capacitors C 1  and C 2  and an inductor I, receives the RF signal from the antenna  202  and produces two out-of-phase inputs (i.e., roughly  180  degree phase shift) that are input to the receiver  200  via input pads  208  and  210 . The in-phase component (I) is provided to a first LNA  212  via input pad  208 , while the quadrature component (Q) is provided to a second LNA  214  via input pad  210 . 
     Each of the LNAs  212  and  214  is operable to amplify their respective I/Q signals and provide the amplified I/Q signals to respective optional gain stages (Gm  216  and Gm  218 ). In addition, the mixer  220  includes two mixers  222  and  224 , each coupled to receive a respective one of the amplified I/Q signals and operable to down-convert the I/Q signals from a radio frequency (RF) within the FM frequency band to a baseband or intermediate frequency (e.g., 200 kHz). Although not shown, it should be understood that the outputs I RX  and Q RX  of the mixers  222  and  224  are input to respective I/Q LPFs and I/Q ADC&#39;s, as shown in  FIG. 3 . 
     In addition, as shown in  FIG. 5 , the impedance of the LNA inputs  208 / 210  is matched to the impedance of the receiver antenna  202 . As shown in  FIG. 5 , the receiver antenna  202  is a 50 ohm antenna, and the impedance at each input pad  208  and  210  is 100 ohms, which produces a series impedance of 200 ohms to the antenna  202 . The balun  206  operates to convert the 200 ohm impedance of the LNAs  212 / 214  into a 50 ohm impedance to match the impedance of the antenna  202 . 
     Furthermore, as shown in  FIG. 5 , the impedance of the LNA input  228  is matched to the impedance of the transmitter antenna  226 . As shown in  FIG. 5 , the transmitter antenna  226  is a loop antenna with an impedance of at least 2 kΩ, a Q of at least 30 and an inductance substantially equal to 120 nH. Therefore, the impedance at the input pad  228  to the LNA is also at least 2 kΩ to match the impedance of the transmitter antenna  226 . 
     Turning now to  FIG. 6 , when the FM receiver  200  is operating in single ended mode, the radio frequency (RF) signal at the input to the receiver  200  is an RF signal with a single phase. Therefore, the balun shown in  FIG. 5  is not needed and the two input pads  208  and  210  to the LNAs  212  and  214  are shorted to provide a single phase to the inputs  208 / 210 . 
     As in  FIG. 5 , each of the LNAs  212  and  214  is operable to amplify the RF signal and provide the amplified RF signal to respective optional gain stages (Gm  216  and Gm  218 ) and respective mixers  222  and  224  to down-convert the amplified RF signal to a near baseband signal. In addition, although not shown, it should be understood that the outputs of the mixers  222  and  224  are input to respective LPFs and ADC&#39;s that also operate in single-ended mode (same phase on both branches). 
     In  FIG. 6 , the impedance of the LNA inputs  208 / 210  is also matched to the impedance of the receiver antenna  202 . Since the inputs  208 / 210  are shorted in single ended mode, the two impedances are in parallel, which produces an impedance of  50  ohms to the antenna  202 . 
     Turning now to  FIG. 7 , the FM receiver  200  is again operating in single ended mode, but the impedance of the LNA inputs  208 / 210  is not matched to the impedance of the receiver antenna  202 . Instead, as shown in  FIG. 7 , the impedance at each input pad  208  and  210  is at least 3 kΩ, thus producing a high impedance (e.g., at least 1.5 kΩ) to the receiver antenna  202 . By providing a high input impedance to the LNAs  212  and  214 , receiver performance can be improved because even if the antenna impedance changes with movement or coupling to other sources of impedance (e.g., user hand), the antenna still detects the same potential across the LNAs  212 / 214 . 
       FIG. 8  illustrates an exemplary programmable low noise amplifier  300  for use within the FM radio receiver in accordance with the present invention. The LNA  300  can correspond, for example, to any of the LNAs  122 ,  124 ,  212 ,  214 ,  230  and  232  shown in previous Figures. The LNA  300  includes an inverter  310  and a variable feedback resistor Rf. In  FIG. 8 , Vi refers to the input voltage, Vo refers to the output voltage, ro refers to the output impedance and Zi refers to the input impedance. The input impedance Zi of the LNA  300  is set according to the following equation: 
     
       
         
           
             
               
                 
                   
                     Zi 
                     = 
                     
                       
                         ro 
                         + 
                         Rf 
                       
                       
                         1 
                         + 
                         
                           gm 
                           · 
                           ro 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     where gm is the gain of the LNA  300 . Thus, as can be seen in Equation 1, the input impedance of the LNA  300  is directly proportional to the resistance of the variable feedback resistor Rf. As such, in order to set the input impedance to the desired value, the processor (shown in  FIG. 3 ) can set the resistance of the variable feedback resistor Rf to a value that will produce the desired input impedance. 
       FIG. 9  is a logic diagram of a method  400  for operating a wireless device including an FM radio receiver in accordance with the present invention. The method begins at step  410 , where a first antenna having a first impedance is connected to the wireless device. At step  420 , a second antenna with a second impedance is connected to the wireless device. The method proceeds at step  430 , where at least one of the first and second antennas is selected, and the method concludes at step  440 , where the selected antenna(s) are coupled to the FM receiver. 
       FIG. 10  is a logic diagram of a method  500  for configuring an FM radio receiver, in accordance with the present invention. The method begins at step  510 , where an antenna is coupled to the FM receiver. At step  520 , the impedance of the antenna is determined, either based on manufacturer specifications or in response to a measured impedance by the FM receiver. At step  530 , a decision is made whether antenna impedance matching of the FM receiver is desired. If so, at step  540 , the impedance of one or more low noise amplifiers (LNAs) within the FM receiver coupled to the antenna is set to produce a matching impedance to the antenna. If not, at step  550 , the impedance of one or more LNAs coupled to the antenna is set to produce an impedance to the antenna that is higher than the antenna impedance. 
     As may be used herein, the terms “substantially” and “approximately” provides an industry-accepted tolerance for its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to fifty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As may also be used herein, the term(s) “coupled to” and/or “coupling” and/or includes direct coupling between items and/or indirect coupling between items via an intervening item (e.g., an item includes, but is not limited to, a component, an element, a circuit, and/or a module) where, for indirect coupling, the intervening item does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As may further be used herein, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two items in the same manner as “coupled to”. As may even further be used herein, the term “operable to” indicates that an item includes one or more of power connections, input(s), output(s), etc., to perform one or more its corresponding functions and may further include inferred coupling to one or more other items. As may still further be used herein, the term “associated with”, includes direct and/or indirect coupling of separate items and/or one item being embedded within another item. 
     The present invention has also been described above with the aid of method steps illustrating the performance of specified functions and relationships thereof. The boundaries and sequence of these functional building blocks and method steps have been arbitrarily defined herein for convenience of description. Alternate boundaries and sequences can be defined so long as the specified functions and relationships are appropriately performed. Any such alternate boundaries or sequences are thus within the scope and spirit of the claimed invention. 
     The present invention has further been described above with the aid of functional building blocks illustrating the performance of certain significant functions. The boundaries of these functional building blocks have been arbitrarily defined for convenience of description. Alternate boundaries could be defined as long as the certain significant functions are appropriately performed. Similarly, flow diagram blocks may also have been arbitrarily defined herein to illustrate certain significant functionality. To the extent used, the flow diagram block boundaries and sequence could have been defined otherwise and still perform the certain significant functionality. Such alternate definitions of both functional building blocks and flow diagram blocks and sequences are thus within the scope and spirit of the claimed invention. One of average skill in the art will also recognize that the functional building blocks, and other illustrative blocks, modules and components herein, can be implemented as illustrated or by discrete components, application specific integrated circuits, processors executing appropriate software and the like or any combination thereof. 
     The preceding discussion has presented an FM receiver and method of operation thereof. As one of ordinary skill in the art will appreciate, other embodiments may be derived from the teaching of the present invention without deviating from the scope of the claims.