Noise reduction in a dual radio frequency receiver

The present invention relates to a dual radio frequency (RF) receiver circuit that includes a first RF mixer and a second RF mixer. The first and second RF mixers may be fed from a common local oscillator or from two separate local oscillators. When fed from two separate local oscillators and when the first and second RF mixers are receiving the same or nearly the same RF channel, the frequency of the RF channel is less than the frequency of one local oscillator and is greater than the frequency of the other local oscillator. This arrangement separates the frequencies of the local oscillators, thereby reducing noise, instability, or both, which may otherwise de-sensitize the dual RF receiver circuit.

FIELD OF THE INVENTION

Embodiments of the present invention relate to radio frequency (RF) mixers used in RF receiver circuitry, which may be used in wireless communications systems.

BACKGROUND OF THE INVENTION

As technology progresses, wireless communication protocols demand increasing rates of data transfer. Therefore, increasingly efficient methods of data encoding and processing are often required. Some wireless systems incorporate dual receiver architectures to simultaneously process data from two different data streams. Such approaches may double data rates when compared with existing architectures. For example, an Enhanced Data Rates for Global Evolution (EDGE) Evolution protocol is a multiple radio frequency (RF) channel protocol. Two data streams are transmitted to a dual receiver, such that each data stream has its own set of radio frequency (RF) channels. Transmission may alternate between the two data steams as each data stream switches its RF channel, such that only one data stream is transmitted at a time.

For example, a first data stream is transmitted on one of a first set of RF channels followed by a second data stream transmitted on one of a second set of RF channels. Then, the first data stream is transmitted on another of the first set of RF channels followed by the second data stream transmitted on another of the second set of RF channels, and so on. On the receive side, while the first data stream is being received by a first side of the dual receiver, a second side of the dual receiver is switching RF channels in preparation to receive the second data stream. Then, while the second data stream is being received by the second side of the dual receiver, a first side of the dual receiver is switching RF channels in preparation to receive the first data stream. Since data is being received by one side of the dual receiver while the other side of the dual receiver is switching RF channels, this approach allows continuous reception of data.

Each side of the dual receiver may have its own local oscillator for selecting the appropriate RF channel, and since each data stream has its own set of RF channels, it may be possible for one side of the dual receiver to be receiving on one RF channel while the other side of the dual receiver is switching to the same or an adjacent RF channel. Therefore, both local oscillators may be tuned to the same or nearly the same frequency. Since both local oscillators may be provided by the same semiconductor die or by a common module, circuit parasitics may introduce noise or instability into the local oscillators that would not be present when the local oscillators are tuned to different frequencies. The noise or instability may de-sensitize either of both sides of the dual receiver, thereby reducing the effective sensitivity of the dual receiver. Thus, there is a need to reduce the noise or instability associated with local oscillators tuned to about the same frequency.

SUMMARY OF THE EMBODIMENTS

The present invention relates to a dual radio frequency (RF) receiver circuit that includes a first RF mixer and a second RF mixer. The first and second RF mixers may be fed from a common local oscillator or from two separate local oscillators. When fed from two separate local oscillators and when the first and the second RF mixers are receiving the same or nearly the same RF channel, the frequency of the RF channel is less than the frequency of one local oscillator and is greater than the frequency of the other local oscillator. This arrangement separates the frequencies of the local oscillators, thereby reducing noise, instability, or both, which may otherwise de-sensitize the dual RF receiver circuit. In one embodiment of the present invention, the frequency of each local oscillator is selected to be either less than or greater than the frequency of its respective RF channel based on maximizing the separation of the frequencies of the local oscillators. In an alternate embodiment of the present invention, the frequency of each local oscillator is selected to be either less than or greater than the frequency of its respective RF channel based on separating a frequency of a local oscillator from interfering RF signals, from spurious RF signals, from an image of an RF channel, or any combination thereof.

When fed from a common local oscillator, a frequency of an RF channel associated with one data stream may be greater than the frequency of the common local oscillator, whereas a frequency of an RF channel associated with another data stream may be less than the frequency of the common local oscillator. The dual RF receiver circuit may be used in a multi-mode wireless communications terminal, which may be capable of receiving highband third generation (3G) RF signals, transmitting highband 3G RF signals, receiving lowband 3G RF signals, transmitting lowband 3G RF signals, receiving highband Enhanced Data Rates for Global Evolution (EDGE) Evolution RF signals, transmitting highband EDGE Evolution RF signals, receiving lowband EDGE Evolution RF signals, transmitting lowband EDGE Evolution signals, or any combination thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a dual radio frequency (RF) receiver circuit that includes a first RF mixer and a second RF mixer. The first and second RF mixers may be fed from a common local oscillator or from two separate local oscillators. When fed from two separate local oscillators and when the first and second RF mixers are receiving the same or nearly the same RF channel, the frequency of the RF channel is less than the frequency of one local oscillator and is greater than the frequency of the other local oscillator. This arrangement separates the frequencies of the local oscillators, thereby reducing noise, instability, or both, which may otherwise de-sensitize the dual RF receiver circuit. In one embodiment of the present invention, the frequency of each local oscillator is selected to be either less than or greater than the frequency of its respective RF channel based on maximizing the separation of the frequencies of the local oscillators. In an alternate embodiment of the present invention, the frequency of each local oscillator is selected to be either less than or greater than the frequency of its respective RF channel based on separating a frequency of a local oscillator from interfering RF signals, from spurious RF signals, from an image of an RF channel, or any combination thereof.

When fed from a common local oscillator, a frequency of an RF channel associated with one data stream may be greater than the frequency of the common local oscillator, whereas a frequency of an RF channel associated with another data stream may be less than the frequency of the common local oscillator. The dual RF receiver circuit may be used in a multi-mode wireless communications terminal, which may be capable of receiving highband third generation (3G) RF signals, transmitting highband 3G RF signals, receiving lowband 3G RF signals, transmitting lowband 3G RF signals, receiving highband Enhanced Data-Rates for Enhanced Data Rates for Global Evolution (EDGE) Evolution RF signals, transmitting highband EDGE Evolution RF signals, receiving lowband EDGE Evolution RF signals, transmitting lowband EDGE Evolution signals, or any combination thereof.

FIG. 1shows a wireless communications terminal10according to one embodiment of the present invention. The wireless communications terminal10includes an antenna12, which receives and provides an RF antenna signal RFANTto receiver front-end circuitry14. The receiver front-end circuitry14provides first and second RF receive signals RFRX1, RFRX2to first and second RF mixers16,18, respectively, based on the RF antenna signal RFANT. The first and second RF mixers16,18down-convert the first and second RF receive signals RFRX1, RFRX2to provide first and second intermediate frequency (IF) signals IF1, IF2, respectively, by mixing the first and second RF receive signals RFRX1, RFRX2with first and second local oscillator signals LO1, LO2, respectively. The first and second RF mixers16,18feed the first and second IF signals IF1, IF2, respectively, to receiver IF de-modulation and processing circuitry20, which further down-converts, de-modulates, or both, the first and second IF signals IF1, IF2to extract modulated data that was embedded in the RF antenna signal RFANT.

The receiver IF de-modulation and processing circuitry20provides a receive baseband signal BBRX, which is based on the modulated data, to baseband processing circuitry22. A first and a second frequency synthesizer24,26provide the first and second local oscillator signals LO1, LO2, respectively. Control circuitry28selects a mixer operating mode and provides a mixer mode select signal MIXMSEL, which is based on the mixer operating mode, to the first and second frequency synthesizers24,26, and to the receiver IF de-modulation and processing circuitry20. The wireless communications terminal10may include system circuitry30, which may be driven by a system clock signal SYSCLK. The system circuitry30may include the control circuitry28, which may be driven by the system clock signal SYSCLK.

The first and second RF mixers16,18may be part of a dual receiver, which may enable continuous data reception. In one embodiment of the wireless communications terminal10, EDGE Evolution data is received by the antenna12. The EDGE Evolution data is received in two data streams, such that each data stream has its own set of RF channels for frequency diversity. Transmission and reception may alternate between the two data streams as each data stream switches its RF channel, such that only one data stream is transmitted at a time

For example, a first data stream is received on one of a first set of RF channels followed by a second data stream received on one of a second set of RF channels. Then, the first data stream is received on another of the first set of RF channels followed by the second data stream received on another of the second set of RF channels, and so on. While the first data stream is being received by a first side of the dual receiver, a second side of the dual receiver is switching RF channels in preparation to receive the second data stream. Then, while the second data stream is being received by the second side of the dual receiver, a first side of the dual receiver is switching RF channels in preparation to receive the first data stream. Since data is being received by one side of the dual receiver while the other side of the dual receiver is switching RF channels, this approach allows continuous reception of data.

FIGS. 2A and 2Bare graphs illustrating the first and second RF receive signals RFRX1, RFRX2, which contain the first and second data streams, respectively. The first data stream includes a first data slot32, which is immediately followed by a second data slot34in the second data stream. The second data slot34is immediately followed by a third data slot36in the first data stream, and the third data slot36is immediately followed by a fourth data slot38in the second data stream, and so on. Reception of the first, second, third, and fourth data slots32,34,36,38provides a continuous flow of data. In alternate embodiments of the wireless communications terminal10, communications protocols other than EDGE Evolution may be used to receive data using two or more data streams.

FIG. 3Ais a graph illustrating the wireless communications terminal10ofFIG. 1in a first mixer operating mode. The antenna12is receiving a first wanted RF signal, which is included in the first RF receive signal RFRX1, having a first wanted center frequency FW1and a second wanted RF signal, which is included in the second RF receive signal RFRX2, having a second wanted center frequency FW2. The first wanted RF signal includes the first data stream and the second wanted RF signal includes the second data stream. The first RF receive signal RFRX1is based on the first wanted RF signal and the second RF receive signal RFRX2is based on the second wanted RF signal. The first wanted RF signal is on one RF channel and the second wanted RF signal is on an adjacent RF channel, such that the second wanted center frequency FW2is greater than the first wanted center frequency FW1. The difference between the first and second wanted center frequencies FW1, FW2is a channel spacing40.

The first local oscillator signal LO1has a first local oscillator frequency FLO1, and the second local oscillator signal LO2has a second local oscillator frequency FLO2. When the first RF mixer16mixes the first RF receive signal RFRX1and the first local oscillator signal LO1, the first IF signal IF1has IF sub-signals at two different center frequencies. The center frequency of one IF sub-signal is at the sum of the first wanted center frequency FW1and the first local oscillator frequency FLO1, and the center frequency of the other IF sub-signal is at the difference between the first wanted center frequency FW1and the first local oscillator frequency FLO1. The IF sub-signal at the sum of the first wanted center frequency FW1and the first local oscillator frequency FLO1is removed by the receiver IF de-modulation and processing circuitry20. The IF sub-signal at the difference between the first wanted center frequency FW1and the first local oscillator frequency FLO1is processed by the receiver IF de-modulation and processing circuitry20. The difference between the first wanted center frequency FW1and the first local oscillator frequency FLO1is a first IF center frequency FIF1.

Similarly, when the second RF mixer18mixes the second RF receive signal RFRX2and the second local oscillator signal LO2, the second IF signal IF2has IF sub-signals at two different center frequencies. The center frequency of one IF sub-signal is at the sum of the second wanted center frequency FW2and the second local oscillator frequency FLO2, and the center frequency of the other IF sub-signal is at the difference between the second wanted center frequency FW2and the second local oscillator frequency FLO2. The IF sub-signal at the sum of the second wanted center frequency FW2and the second local oscillator frequency FLO2is removed by the receiver IF de-modulation and processing circuitry20. The IF sub-signal at the difference between the second wanted center frequency FW2and the second local oscillator frequency FLO2is processed by the receiver IF de-modulation and processing circuitry20. The difference between the second wanted center frequency FW2and the second local oscillator frequency FLO2is a second IF center frequency FIF2.

The first local oscillator frequency FLO1may be either greater than or less than the first wanted center frequency FW1. Similarly, the second local oscillator frequency FLO2may be either greater than or less than the second wanted center frequency FW2. In the first mixer operating mode, the first local oscillator frequency FLO1is less than the first wanted center frequency FW1, and the second local oscillator frequency FLO2is greater than the second wanted center frequency FW2. When the second wanted center frequency FW2is greater than or equal to the first wanted center frequency FW1, the first mixer operating mode provides the greatest separation between the first local oscillator frequency FLO1and the second local oscillator frequency FLO2; therefore, the first mixer operating mode was selected. If the first local oscillator frequency FLO1is greater than the first wanted center frequency FW1, the second local oscillator frequency FLO2is less than the second wanted center frequency FW2, or both, the separation between the first local oscillator frequency FLO1and the second local oscillator frequency FLO2may be insufficient to prevent an unacceptable level of noise, instability, or both, as a result of interaction between the first and second frequency synthesizers24,26.

FIG. 3Bis a graph illustrating the wireless communications terminal10ofFIG. 1in a first mixer operating mode. The antenna12is receiving the first wanted RF signal, which is included in the first RF receive signal RFRX1, having the first wanted center frequency FW1and the second wanted RF signal, which is included in the second RF receive signal RFRX2, having the second wanted center frequency FW2. The first wanted RF signal includes the first data stream and the second wanted RF signal includes the second data stream. The first RF receive signal RFRX1is based on the first wanted RF signal and the second RF receive signal RFRX2is based on the second wanted RF signal. The first wanted RF signal and the second wanted RF signal are both on the same RF channel, such that the second wanted center frequency FW2is about equal to the first wanted center frequency FW1. The first mixer operating mode was selected to provide the greatest separation between the first local oscillator frequency FLO1and the second local oscillator frequency FLO2.

FIG. 3Cis a graph illustrating the wireless communications terminal10ofFIG. 1in a second mixer operating mode. The antenna12is receiving the first wanted RF signal, which is included in the first RF receive signal RFRX1, having the first wanted center frequency FW1and the second wanted RF signal, which is included in the second RF receive signal RFRX2, having the second wanted center frequency FW2. The first wanted RF signal includes the first data stream and the second wanted RF signal includes the second data stream. The first RF receive signal RFRX1is based on the first wanted RF signal and the second RF receive signal RFRX2is based on the second wanted RF signal. The first wanted RF signal is on one RF channel and the second wanted RF signal is on an adjacent RF channel, such that the second wanted center frequency FW2is less than the first wanted center frequency FW1. The difference between the first and second wanted center frequencies FW1, FW2is the channel spacing40.

In the second mixer operating mode, the first local oscillator frequency FLO1is greater than the first wanted center frequency FW1, and the second local oscillator frequency FLO2is less than the second wanted center frequency FW2. When the second wanted center frequency FW2is less than or equal to the first wanted center frequency FW1, the second mixer operating mode provides the greatest separation between the first local oscillator frequency FLO1and the second local oscillator frequency FLO2; therefore, the second mixer operating mode was selected. If the first local oscillator frequency FLO1is less than the first wanted center frequency FW1, the second local oscillator frequency FLO2is greater than the second wanted center frequency FW2, or both, the separation between the first local oscillator frequency FLO1and the second local oscillator frequency FLO2may be insufficient to prevent an unacceptable level of noise, instability, or both, as a result of interaction between the first and second frequency synthesizers24,26.

FIG. 4Ais a graph illustrating the wireless communications terminal10ofFIG. 1in the first mixer operating mode in the presence of an interfering RF signal RFINT. The second wanted RF signal, which is included in the second RF receive signal RFRX2, is separated from the first wanted RF signal, which is included in the first RF receive signal RFRX1, by three RF channels; therefore, the difference between the first wanted center frequency FW1and the second wanted center frequency FW2is equal to about three channel spacings40, which provides greater than three channel spacings40between the first local oscillator frequency FLO1and the second local oscillator frequency FLO2.

Since the second local oscillator frequency FLO2is greater than the second wanted center frequency FW2, the second RF mixer18has an image frequency FIMAGEof the second wanted center frequency FW2that is greater than the second local oscillator frequency FLO2. The difference between the image frequency FIMAGEand the second local oscillator frequency FLO2is the second IF center frequency FIF2. Any received signals at the image frequency FIMAGEmay interfere with proper reception of the second wanted RF signal. As illustrated inFIG. 4A, the frequency of the interfering RF signal RFINTis about equal to the image frequency FIMAGE; therefore, the interfering RF signal RFINTmay interfere with proper reception of the second wanted RF signal. To minimize effects of the interfering RF signal RFINT, a different mixer operating mode may be selected to move the image frequency FIMAGEaway from the frequency of the interfering RF signal RFINT.

FIG. 4Bis a graph illustrating the wireless communications terminal10ofFIG. 1in a third mixer operating mode. The first and second wanted RF signals, which are included in the first and second RF receive signals RFRX1, RFRX2, and the interfering RF signal RFINTare unchanged fromFIG. 4A. However, in the third mixer operating mode, both the first and the second local oscillator frequencies FLO1, FLO2are less than the first and the second wanted center frequencies FW1, FW2, respectively. By moving the second local oscillator frequency FLO2from being greater than the second wanted center frequency FW2to being less than the second wanted center frequency FW2, the image frequency FIMAGEis moved away from the frequency of the interfering RF signal RFINT. However, the separation between the first and the second local oscillator frequencies FLO1, FLO2is reduced, which may be problematic in some situations. Since the separation between the first wanted center frequency FW1and the second wanted center frequency FW2is equal to about three channel spacings40, the first and second local oscillator signals LO1, LO2, may not interfere with one another. In some embodiments of the present invention, mixer operating mode selection may be based on a trade-off between increasing the separation between the first and the second local oscillator frequencies FLO1, FLO2and increasing the separation between an image frequency FIMAGEand a frequency of an interfering RF signal RFINT.

FIG. 5Ais a graph illustrating the wireless communications terminal10ofFIG. 1in the first mixer operating mode in the presence of a spurious RF signal RFSPUR. The second wanted RF signal, which is included in the second RF receive signal RFRX2, is separated from the first wanted RF signal, which is included in the first RF receive signal RFRX1, by three RF channels; therefore, the difference between the first wanted center frequency FW1and the second wanted center frequency FW2is equal to about three channel spacings40, which provides greater than three channel spacings40between the first local oscillator frequency FLO1and the second local oscillator frequency FLO2.

The spurious RF signal RFSPURmay be a harmonic of the system clock signal SYSCLK and may be coupled into the signal path of receive circuitry through circuit parasitics. As illustrated inFIG. 5A, the frequency of the spurious RF signal RFSPURis about equal to the first local oscillator frequency FLO1; therefore, the spurious RF signal RFSPURmay interfere with proper reception of the first wanted RF signal. To minimize effects of the spurious RF signal RFSPUR, a different mixer operating mode may be selected to move the first local oscillator frequency FLO1away from the frequency of the spurious RF signal RFSPUR.

FIG. 5Bis a graph illustrating the wireless communications terminal10ofFIG. 1in a fourth mixer operating mode. The first and second wanted RF signals, which are included in the first and second RF receive signals RFRX1, RFRX2, and the spurious RF signal RFSPURare unchanged fromFIG. 5A. However, in the fourth mixer operating mode, both the first and the second local oscillator frequencies FLO1, FLO2are greater than the first and the second wanted center frequencies FW1, FW2, respectively. By moving the first local oscillator frequency FLO1from being less than the first wanted center frequency FW1to being greater than the first wanted center frequency FW1, the first local oscillator frequency FLO1is moved away from the frequency of the spurious RF signal RFSPUR. However, the separation between the first and the second local oscillator frequencies FLO1, FLO2is reduced, which may be problematic in some situations. Since the separation between the first wanted center frequency FW1and the second wanted center frequency FW2is equal to about three channel spacings40, the first and second local oscillator signals LO1, LO2, may not interfere with one another. In some embodiments of the present invention, mixer operating mode selection may be based on a trade-off between increasing the separation between the first and the second local oscillator frequencies FLO1, FLO2and increasing the separation between one of the first and the second local oscillator frequencies FLO1, FLO2and a frequency of a spurious RF signal RFSPUR.

In some embodiments of the present invention, any of the mixer operating modes may be omitted, selection of the mixer operating mode may be based on providing adequate separation between the first and the second local oscillator frequencies FLO1, FLO2, substantially maximizing separation between the first and the second local oscillator frequencies FLO1, FLO2, providing adequate separation between the first local oscillator frequency FLO1and a frequency of a spurious RF signal RFSPUR, providing adequate separation between the second local oscillator frequency FLO2and a frequency of a spurious RF signal RFSPUR, providing adequate separation between an image frequency FIMAGEof the first wanted center frequency FW1and a frequency of an interfering RF signal RFINT, providing adequate separation between an image frequency FIMAGEof the second wanted center frequency FW2and a frequency of an interfering RF signal RFINT, or any combination thereof.

FIG. 6shows details of the first and second frequency synthesizers24,26illustrated inFIG. 1. The first frequency synthesizer24includes a first phase-locked loop42having a first voltage controlled oscillator (VCO)44, which provides a first VCO signal VCO1to a first divider46. The first phase-locked loop42includes frequency synthesis circuitry, such as the first VCO44, for synthesizing any needed frequencies for the first VCO signal VCO1. The first divider46divides the first VCO signal VCO1to provide the first local oscillator signal LO1. Similarly, the second frequency synthesizer26includes a second phase-locked loop48having a second VCO50, which provides a second VCO signal VCO2to a second divider52. The second phase-locked loop48includes frequency synthesis circuitry, such as the second VCO50, for synthesizing any needed frequencies for the second VCO signal VCO2. The second divider52divides the second VCO signal VCO2to provide the second local oscillator signal LO2. The first and second phase-locked loops42,48are used to synthesize any frequencies needed to receive specific RF channels. However, the first and second VCOs44,50may be particularly susceptible to circuit parasitics and may interfere with each other when separation between the first and second VCO signals VCO1, VCO2is inadequate. By including the first and second dividers46,52, differences between the first and second local oscillator frequencies FLO1, FLO2are multiplied between the first and second VCO signals VCO1, VCO2.

In a first exemplary embodiment of the present invention, the wireless communications terminal10ofFIG. 1is in a first mixer operating mode as illustrated inFIG. 3A. The channel spacing40is about 200 kilohertz, the first and second IF center frequencies FIF1, FIF2are between about 120 kilohertz and 175 kilohertz, and the first and second dividers46,52are divide-by-one dividers. Therefore, the difference between the first and second local oscillator frequencies FLO1, FLO2is between about 440 kilohertz and 550 kilohertz.

In a second exemplary embodiment of the present invention, the wireless communications terminal10ofFIG. 1is in a first mixer operating mode as illustrated inFIG. 3A. The channel spacing40is about 200 kilohertz, the first and second IF center frequencies FIF1, FIF2are between about 120 kilohertz and 175 kilohertz, and the first and second dividers46,52are divide-by-two dividers. Therefore, the difference between the first and second local oscillator frequencies FLO1, FLO2is between about 880 kilohertz and 1100 kilohertz.

In a third exemplary embodiment of the present invention, the wireless communications terminal10ofFIG. 1is in a first mixer operating mode as illustrated inFIG. 3A. The channel spacing40is about 200 kilohertz, the first and second IF center frequencies FIF1, FIF2are between about 120 kilohertz and 175 kilohertz, and the first and second dividers46,52are divide-by-four dividers. Therefore, the difference between the first and second local oscillator frequencies FLO1, FLO2is between about 1760 kilohertz and 2200 kilohertz.

FIG. 7shows the wireless communications terminal10according to an alternate embodiment of the present invention. The wireless communications terminal10is similar to the wireless communications terminal10illustrated inFIG. 1, except that inFIG. 1the first and second RF receive signals RFRX1, RFRX2are single-ended signals, whereas inFIG. 7the RF receive signals RFRX1, RFRX2are replaced with differential signals. Specifically, the first RF receive signal RFRX1is replaced with a first positive RF receive signal RFRX1Pand a first negative RF receive signal RFRX1N. Similarly, the second RF receive signal RFRX2is replaced with a second positive RF receive signal RFRX2Pand a second negative RF receive signal RFRX2N. The first positive RF receive signal RFRX1Pis phase-shifted from the first negative RF receive signal RFRX1Nby about 180 degrees. Similarly, the second positive RF receive signal RFRX2Pis phase-shifted from the second negative RF receive signal RFRX2Nby about 180 degrees. In other embodiments of the present invention, any of the first and second local oscillator signals LO1, LO2and the first and second IF signals IF1, IF2may be differential signals.

FIG. 8shows the wireless communications terminal10according to an additional embodiment of the present invention. The wireless communications terminal10is similar to the wireless communications terminal10illustrated inFIG. 1, except that inFIG. 8the second frequency synthesizer26has been omitted. The second RF mixer18is fed with the first local oscillator signal LO1instead of the second local oscillator signal LO2.

FIG. 9is a graph illustrating operation of the wireless communications terminal10ofFIG. 8. Since only the first local oscillator signal LO1is available, the difference between the first local oscillator frequency FLO1and the first wanted center frequency FW1is the first IF center frequency FIF1, and the difference between the first local oscillator frequency FLO1and the second wanted center frequency FW2is the second IF center frequency FIF2. If the first and second IF center frequencies FIF1, FIF2are about equal and constant, then only four combinations are possible. In the first combination, the first wanted center frequency FW1is less than the first local oscillator frequency FLO1, the second wanted center frequency FW2is greater than the first local oscillator frequency FLO1, and the difference between the first and second wanted center frequencies FW1, FW2is the channel spacing40, as illustrated inFIG. 9.

In the second combination (not shown), the first wanted center frequency FW1is greater than the first local oscillator frequency FLO1, the second wanted center frequency FW2is less than the first local oscillator frequency FLO1, and the difference between the first and second wanted center frequencies FW1, FW2is the channel spacing40. In the third combination (not shown), both the first and second wanted RF signals are on the same RF channel and the first and second wanted center frequencies FW1, FW2are equal to one another and are less than the first local oscillator frequency FLO1. In the fourth combination (not shown), both the first and second wanted RF signals are on the same RF channel and the first and second wanted center frequencies FW1, FW2are equal to one another and are greater than the first local oscillator frequency FLO1. Eliminating the second local oscillator signal LO2significantly restricts configuration combinations; however, without the second local oscillator signal LO2, interactions between the first and second local oscillator signals LO1, LO2are eliminated.

FIG. 10shows RF transmitter circuitry54added to the wireless communications terminal10illustrated inFIG. 1. The receiver front-end circuitry14is replaced with RF front-end circuitry56. The wireless communications terminal10illustrated inFIG. 10may be a multi-mode terminal capable of supporting multiple communications protocols. In an exemplary embodiment of the present invention, the wireless communications terminal10may operate using one or more EDGE Evolution communications protocols, one or more 3G communications protocols, or any combination thereof. The baseband processing circuitry22provides a transmit baseband signal BBTX, which includes data to be transmitted, to the RF transmitter circuitry54. The RF transmitter circuitry54provides a first RF transmit signal RFTX1, a second RF transmit signal RFTX2, a third RF transmit signal RFTX3, a fourth RF transmit signal RFTX4, and a fifth RF transmit signal RFTX5to the RF front-end circuitry56based on the transmit baseband signal BBTX.

The control circuitry28provides an RF mode select signal RFMSEL to the RF front-end circuitry56to select desired RF communication modes. When transmitting, receiving, or both, 3G signals, the wireless communications terminal10may be operating in a first RF operating mode, and when transmitting, receiving, or both, EDGE Evolution signals, the wireless communications terminal10may be operating in a second RF operating mode. The antenna12receives RF signals and provides the RF antenna signal RFANTto the RF front-end circuitry56based on the received RF signals. The RF front-end circuitry56provides the first and second RF receive signals RFRX1, RFRX2based on the RF antenna signal RFANTand the RF mode select signal RFMSEL. The RF front-end circuitry56provides appropriate RF transmit signals to the antenna12using the RF antenna signal RFANTbased on one or more of the first, second, third, fourth, and fifth RF transmit signals RFTX1, RFTX2, RFTX3, RFTX4, RFTX5and the RF mode select signal RFMSEL.

FIG. 11shows the wireless communications terminal10according to another embodiment of the present invention. The wireless communications terminal10illustrated inFIG. 11is similar to the wireless communications terminal10illustrated inFIG. 10except that the second frequency synthesizer26provides an RF carrier signal RFCARto the RF transmitter circuitry54, and the second local oscillator signal LO2is based on either the first local oscillator signal LO1or the RF carrier signal RFCAR. A multiplexer58receives the first local oscillator signal LO1, the RF carrier signal RFCAR, and a multiplexer select signal MUXSEL. The multiplexer58provides the second local oscillator signal LO2to the second RF mixer18. The control circuitry28provides the multiplexer select signal MUXSEL, which is used to select either the first local oscillator signal LO1or the RF carrier signal RFCARto provide the second local oscillator signal LO2.

In an exemplary embodiment of the present invention, when the wireless communications terminal10is operating using a 3G communications protocol, since transmission and reception of RF signals may occur simultaneously, the multiplexer58is configured such that both the first and second RF mixers16,18use the first local oscillator signal LO1for mixing and the RF transmitter circuitry54uses the RF carrier signal RFCARfor transmitting. When the wireless communications terminal10is operating using an EDGE Evolution communications protocol, since transmission and reception of RF signals do not occur simultaneously, the multiplexer58is configured such that the first RF mixer16uses the first local oscillator signal LO1for mixing, the second RF mixer18uses the RF carrier signal RFCARfor mixing, and the RF transmitter circuitry54uses the RF carrier signal RFCARfor transmitting. Since the second RF mixer18and the RF transmitter circuitry54share a frequency synthesizer, power, space, complexity, and noise are reduced.

FIG. 12shows 3G diversity receiver front-end circuitry60added to the wireless communications terminal10illustrated inFIG. 10according to one embodiment of the present invention. The 3G diversity receiver front-end circuitry60receives the RF mode select signal RFMSEL. A diversity antenna62receives RF signals, which are fed to the 3G diversity receiver front-end circuitry60. The 3G diversity receiver front-end circuitry60provides the second RF receive signal RFRX2based on received RF signals and the RF mode select signal RFMSEL.

Since the first and second RF mixers16,18receive the first and second local oscillator signals LO1, LO2from the first and second frequency synthesizers, respectively, configuration flexibility is provided in receiving 3G normal signals and 3G diversity signals. Since 3G communications may include simultaneous transmission and reception of RF signals, the RF transmitter circuitry54may require a separate frequency synthesizer (not shown).

In an alternate embodiment of the present invention, the wireless communications terminal10may include the multiplexer58illustrated inFIG. 11. When transmitting and receiving 3G signals, the multiplexer select signal MUXSEL configures the multiplexer58to provide the second local oscillator signal LO2to the second RF mixer18based on the first local oscillator signal LO1, and the second frequency synthesizer26provides the RF carrier signal RFCARto the RF transmitter circuitry54. When receiving EDGE Evolution signals, the multiplexer select signal MUXSEL configures the multiplexer58to provide the second local oscillator signal LO2to the second RF mixer18based on the RF carrier signal RFCARfrom the second frequency synthesizer26. Since EDGE Evolution signals are not transmitted and received simultaneously, the second frequency synthesizer26may be used to provide the RF carrier signal RFCARto the RF transmitter circuitry54for transmitting EDGE Evolution signals, and the second frequency synthesizer26may be used to provide the second local oscillator signal LO2to the second RF mixer18for receiving EDGE Evolution signals.

In an exemplary embodiment of the present invention, when the wireless communications terminal10is operating using a 3G communications protocol, the 3G diversity receiver front-end circuitry60provides the second RF receive signal RFRX2based on received RF signals, and the RF front-end circuitry56does not provide the second RF receive signal RFRX2. The RF front-end circuitry56may include switching circuitry to effectively disconnect the RF front-end circuitry56from the second RF mixer18when the 3G diversity receiver front-end circuitry60provides the second RF receive signal RFRX2. When the wireless communications terminal10is operating using an EDGE Evolution communications protocol, the 3G diversity receiver front-end circuitry60does not provide the second RF receive signal RFRX2, and the RF front-end circuitry56provides the second RF receive signal RFRX2based on received RF signals. The 3G diversity receiver front-end circuitry60may include switching circuitry to effectively disconnect the 3G diversity receiver front-end circuitry60from the second RF mixer18when the RF front-end circuitry56provides the second RF receive signal RFRX2.

FIG. 13shows details of the RF front-end circuitry56illustrated inFIG. 10according to one embodiment of the present invention. The RF front-end circuitry56includes an RF diplexer64, an RF switch66, a first 3G highband duplexer68, a second 3G highband duplexer70, a highband receive surface acoustic wave (SAW) filter72, a lowband receive SAW filter74, a 3G lowband duplexer76, and a receive low noise amplifier (LNA) and cross-bar switch array78. The RF diplexer64includes an antenna terminal ANT coupled to the antenna12(not shown) for sending and receiving the antenna signals RFANT. Additionally, the RF diplexer64includes a highband terminal HIBAND, a lowband terminal LOBAND, a bidirectional highpass filter (not shown) coupled between the antenna terminal ANT and the highband terminal HIBAND, and a bidirectional lowpass filter (not shown) coupled between the antenna terminal ANT and the lowband terminal LOBAND. The bidirectional highpass filter allows only highband signals to pass between the antenna terminal ANT and the highband terminal HIBAND, and the bidirectional lowpass filter allows only lowband signals to pass between the antenna terminal ANT and the lowband terminal LOBAND. The RF diplexer64may support simultaneous transmission of highband signals, reception of highband signals, transmission of lowband signals, reception of lowband signals, or any combination thereof.

The RF switch66includes a highband terminal HIBAND, a lowband terminal LOBAND, a first 3G highband terminal 3GHB1, a second 3G highband terminal 3GHB2, an EDGE highband receive terminal EGHBRX, an EDGE lowband receive terminal EGLBRX, a 3G lowband terminal 3GLB, an EDGE highband transmit terminal EGHBTX, and an EDGE lowband transmit terminal EGLBTX. The highband terminal HIBAND of the RF switch66is coupled to the highband terminal HIBAND of the RF diplexer64, and the lowband terminal LOBAND of the RF switch66is coupled to the lowband terminal LOBAND of the RF diplexer64. The RF switch66receives the RF mode select signal RFMSEL and configures internal switching elements based on the RF mode select signal RFMSEL.

When the wireless communications terminal10is transmitting and receiving first highband 3G signals, the RF switch66is configured to couple the first 3G highband terminal 3GHB1 to the highband terminal HIBAND. When the wireless communications terminal10is transmitting and receiving second highband 3G signals, the RF switch66is configured to couple the second 3G highband terminal 3GHB2 to the highband terminal HIBAND. When the wireless communications terminal10is transmitting and receiving lowband 3G signals, the RF switch66is configured to couple the 3G lowband terminal 3GLB to the lowband terminal LOBAND. When the wireless communications terminal10is receiving highband EDGE Evolution signals, the RF switch66is configured to couple the EDGE highband receive terminal EGHBRX to the highband terminal HIBAND.

When the wireless communications terminal10is transmitting highband EDGE Evolution signals, the RF switch66is configured to couple the EDGE highband transmit terminal EGHBTX to the highband terminal HIBAND. The EDGE highband transmit terminal EGHBTX receives the fourth RF transmit signal RFTX4. When the wireless communications terminal10is receiving lowband EDGE Evolution signals, the RF switch66is configured to couple the EDGE lowband receive terminal EGLBRX to the lowband terminal LOBAND. When the wireless communications terminal10is transmitting lowband EDGE Evolution signals, the RF switch66is configured to couple the EDGE lowband transmit terminal EGLBTX to the lowband terminal LOBAND. The EDGE lowband transmit terminal EGLBTX receives the fifth RF transmit signal RFTX5.

The first 3G highband duplexer68includes an antenna terminal ANT, a transmit terminal TX, a receive terminal RX, a receive bandpass filter (not shown) coupled between the antenna terminal ANT and the receive terminal RX, and a transmit bandpass filter (not shown) coupled between the antenna terminal ANT and the transmit terminal TX. The antenna terminal ANT is coupled to the first 3G highband terminal 3GHB1 of the RF switch66, the transmit terminal TX receives the first RF transmit signal RFTX1, and the receive terminal RX is coupled to a first 3G highband input 3GHBI1 to the receive LNA and cross-bar switch array78.

The first 3G highband duplexer68may allow simultaneous transmission and reception of first highband 3G signals. Typically, a passband of the receive bandpass filter does not overlap a passband of the transmit bandpass filter. The receive bandpass filter allows only signals within its passband to pass from the antenna terminal ANT to the receive terminal RX, and the transmit bandpass filter allows only signals within its passband to pass from the transmit terminal TX to the antenna terminal ANT.

The second 3G highband duplexer70includes an antenna terminal ANT, a transmit terminal TX, a receive terminal RX, a receive bandpass filter (not shown) coupled between the antenna terminal ANT and the receive terminal RX, and a transmit bandpass filter (not shown) coupled between the antenna terminal ANT and the transmit terminal TX. The antenna terminal ANT is coupled to the second 3G highband terminal 3GHB2 of the RF switch66, the transmit terminal TX receives the second RF transmit signal RFTX2, and the receive terminal RX is coupled to a second 3G highband input 3GHBI2 to the receive LNA and cross-bar switch array78.

The second 3G highband duplexer70may allow simultaneous transmission and reception of second highband 3G signals. Typically, a passband of the receive bandpass filter does not overlap a passband of the transmit bandpass filter. The receive bandpass filter allows only signals within its passband to pass from the antenna terminal ANT to the receive terminal RX, and the transmit bandpass filter allows only signals within its passband to pass from the transmit terminal TX to the antenna terminal ANT.

The 3G lowband duplexer76includes an antenna terminal ANT, a transmit terminal TX, a receive terminal RX, a receive bandpass filter (not shown) coupled between the antenna terminal ANT and the receive terminal RX, and a transmit bandpass filter (not shown) coupled between the antenna terminal ANT and the transmit terminal TX. The antenna terminal ANT is coupled to the 3G lowband terminal 3GLB of the RF switch66, the transmit terminal TX receives the third RF transmit signal RFTX3, and the receive terminal RX is coupled to a 3G lowband input 3GLBI to the receive LNA and cross-bar switch array78.

The 3G lowband duplexer76may allow simultaneous transmission and reception of lowband 3G signals. Typically, a passband of the receive bandpass filter does not overlap a passband of the transmit bandpass filter. The receive bandpass filter allows only signals within its passband to pass from the antenna terminal ANT to the receive terminal RX, and the transmit bandpass filter allows only signals within its passband to pass from the transmit terminal TX to the antenna terminal ANT.

The highband receive SAW filter72includes an input terminal IN, an output terminal OUT, and a receive bandpass filter (not shown) coupled between the input terminal IN and the output terminal OUT. The input terminal IN is coupled to the EDGE highband receive terminal EGHBRX of the RF switch66, and the output terminal OUT is coupled to an EDGE highband input EGHBI to the receive LNA and cross-bar switch array78. The receive bandpass filter allows only signals within a passband to pass from the input terminal IN to the output terminal OUT.

The lowband receive SAW filter74includes an input terminal IN, an output terminal OUT, and a receive bandpass filter (not shown) coupled between the input terminal IN and the output terminal OUT. The input terminal IN is coupled to the EDGE lowband receive terminal EGLBRX of the RF switch66, and the output terminal OUT is coupled to an EDGE lowband input EGLBI to the receive LNA and cross-bar switch array78. The receive bandpass filter allows only signals within a passband to pass from the input terminal IN to the output terminal OUT.

The receive LNA and cross-bar switch array78includes the first 3G highband input 3GHBI1, the second 3G highband input 3GHBI2, the 3G lowband input 3GLBI, the EDGE highband input EGHBI, the EDGE lowband input EGLBI, a first output OUT1, which provides the first RF receive signal RFRX1, and a second output OUT2, which provides the second RF receive signal RFRX2. The receive LNA and cross-bar switch array78includes five LNAs (not shown) and a cross-bar switch array (not shown). Each of the first 3G highband input 3GHBI1, the second 3G highband input 3GHBI2, the 3G lowband input 3GLBI, the EDGE highband input EGHBI, and the EDGE lowband input EGLBI feeds an input to a corresponding LNA. Outputs from the LNAs feed the cross-bar switch array, which is configured to couple one or more outputs from the LNAs to the first output OUT1, the second output OUT2, or both, based on the RF mode select signal RFMSEL.

In an exemplary embodiment of the present invention, when the wireless communications terminal10is transmitting and receiving first highband 3G signals, the output of the LNA associated with the first 3G highband input 3GHBI1 is coupled to the first output OUT1. When the wireless communications terminal10is transmitting and receiving second highband 3G signals, the output of the LNA associated with the second 3G highband input 3GHBI2 is coupled to the first output OUT1. When the wireless communications terminal10is transmitting and receiving lowband 3G signals, the output of the LNA associated with the 3G lowband input 3GLBI is coupled to the first output OUT1, when the wireless communications terminal10is receiving highband EDGE Evolution signals, the output of the LNA associated with the EDGE highband input EGHBI is coupled to both the first output OUT1and the second output OUT2. When the wireless communications terminal10is receiving lowband EDGE Evolution signals, the output of the LNA associated with the EDGE lowband input EGLBI is coupled to both the first output OUT1and the second output OUT2. When the wireless communications terminal10is simultaneously receiving highband EDGE Evolution signals and lowband EDGE Evolution signals, the output of the LNA associated with the EDGE highband input EGHBI is coupled to the first output OUT1and the output of the LNA associated with the EDGE lowband input EGLBI is coupled to the second output OUT2.

When the output of the LNA associated with the EDGE highband input EGHBI is driving both the first output OUT1and the second output OUT2, the drive strength of the output may be increased to compensate for driving two outputs instead of one output. Similarly, when the output of the LNA associated with the EDGE lowband input EGLBI is driving both the first output OUT1and the second output OUT2, the drive strength of the output may be increased to compensate for driving two outputs instead of one output.

In alternate embodiments of the present invention, the RF diplexer64may be omitted, such that the wireless communications terminal10supports either highband signals or lowband signals. The RF switch66may support any number of 3G highband signals, 3G lowband signals, EDGE Evolution highband transmit signals, EDGE Evolution highband receive signals, EDGE Evolution lowband transmit signals, EDGE Evolution lowband receive signals, or any combination thereof. Any number of 3G duplexers68,70,76may be added or omitted, any number of receive SAW filters72,74may be added or omitted, or any combination thereof. The receive LNA and cross-bar switch array78may support any number of 3G highband signals, 3G lowband signals, EDGE Evolution lowband receive signals, EDGE Evolution highband receive signals, or any combination thereof.

FIG. 14shows details of the receive LNA and cross-bar switch array78illustrated inFIG. 13according to one embodiment of the present invention. The receive LNA and cross-bar switch array78includes a first LNA80, a second LNA82, a third LNA84, a fourth LNA86, a fifth LNA88, a cross-bar switch90, drive strength control circuitry92, and cross-bar switch control circuitry94. The first 3G highband input 3GHBI1 is coupled to an input to the first LNA80, the EDGE highband input EGHBI is coupled to an input to the second LNA82, the 3G lowband input 3GLBI is coupled to an input to the third LNA84, the second 3G highband input 3GHBI2 is coupled to an input to the fourth LNA86, and the EDGE lowband input EGLBI is coupled to an input to the fifth LNA88. Each of the first, second, third, fourth, and fifth LNAs80,82,84,86,88has an output coupled to the cross-bar switch90, and each of the first, second, third, fourth, and fifth LNAs80,82,84,86,88amplifies an RF signal at its input to provide an amplified signal at its corresponding output.

The RF mode select signal RFMSEL is fed to the drive strength control circuitry92and the cross-bar switch control circuitry94. The drive strength control circuitry92provides a first drive strength control signal DSC1, a second drive strength control signal DSC2, a third drive strength control signal DSC3, a fourth drive strength control signal DSC4, and a fifth drive strength control signal DSC5to the first, second, third, fourth, and fifth LNAs80,82,84,86,88, respectively, based on the RF mode select signal RFMSEL. The cross-bar switch90has a first node (not shown) coupled to the first output OUT1and a second node (not shown) coupled to the second output OUT2. The cross-bar switch control circuitry94selects a configuration of the cross-bar switch90based on the RF mode select signal RFMSEL. The cross-bar switch90may be configured such that the first output OUT1may be coupled to the output of one of the first, second, third, fourth, and fifth LNAs80,82,84,86,88and the second output OUT2may be coupled to the output of one of the first, second, third, fourth, and fifth LNAs80,82,84,86,88.

When the output of one of the first, second, third, fourth, and fifth LNAs80,82,84,86,88is coupled to both the first and second outputs OUT1, OUT2, the drive strength of the LNA may be increased to compensate for driving two loads instead of a single load. Any outputs of the first, second, third, fourth, and fifth LNAs80,82,84,86,88that are coupled to only one of the first and second outputs OUT1, OUT2, or not coupled to an output, may be configured to provide a normal drive strength.

In an exemplary embodiment of the present invention, when the wireless communications terminal10is transmitting and receiving first highband 3G signals, the cross-bar switch90may be configured such that the output of the first LNA80, which is associated with the first 3G highband input 3GHBI1, is coupled to the first output OUT1, when the wireless communications terminal10is transmitting and receiving second highband 3G signals, the cross-bar switch90may be configured such that the output of the fourth LNA86, which is associated with the second 3G highband input 3GHBI2, is coupled to the first output OUT1, and when the wireless communications terminal10is transmitting and receiving lowband 3G signals, the cross-bar switch90may be configured such that the output of the third LNA84, which is associated with the 3G lowband input 3GLBI, is coupled to the first output OUT1. When the output of the first, third, or fourth LNA80,84,86is driving just the first output OUT1, the output of the respective LNA may be configured to provide normal drive strength.

When the wireless communications terminal10is receiving highband EDGE Evolution signals, the cross-bar switch90may be configured such that the output of the second LNA82, which is associated with the EDGE highband input EGHBI, is coupled to both the first output OUT1and the second output OUT2, and when the wireless communications terminal10is receiving lowband EDGE Evolution signals, the cross-bar switch90may be configured such that the output of the fifth LNA88, which is associated with the EDGE lowband input EGLBI, is coupled to both the first output OUT1and the second output OUT2. When the output of the second or fifth LNA82,88is driving both the first output OUT1and the second output OUT2, the drive strength of the output of the respective LNA may be increased to compensate for driving two outputs instead of one output.

Some of the circuitry previously described may use discrete circuitry, integrated circuitry, programmable circuitry, non-volatile circuitry, volatile circuitry, software executing instructions on computing hardware, firmware executing instructions on computing hardware, the like, or any combination thereof. The computing hardware may include mainframes, micro-processors, micro-controllers, digital signal processors (DSPs), the like, or any combination thereof.