WO2016027134A1

WO2016027134A1 - Feedback transmitter and receiver sharing

Info

Publication number: WO2016027134A1
Application number: PCT/IB2014/064026
Authority: WO
Inventors: Somsack David SYCHALEUN; Bi Pham; Buu DAM; Chunyun Jian
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2014-08-22
Filing date: 2014-08-22
Publication date: 2016-02-25
Anticipated expiration: 2017-02-22

Abstract

A method and system for sharing an analog-to-digital (A/D) converter in a transceiver are disclosed. The disclosure provides a frequency division duplex (FDD) radio and a time division duplex (TDD) transceiver. The FDD or TDD radio includes at least one transceiver. Each transceiver has a transmitter observation receiver (TOR) configured to produce a first analog signal. A receiver circuit is configured to produce a second analog signal. The signal paths of the TOR and the receiver circuit are continuously closed paths not sharing any elements in common and not divided into I and Q channels. A shared A/D converter is configured to receive the analog signals from all of the TORs and receiver circuits of the transceivers and converts these signals to digital signals.

Description

FEEDBACK TRANSMITTER AND RECEIVER SHARING

TECHNICAL FIELD

The present disclosure relates to wireless communications and in particular, to radio transceivers.

BACKGROUND

In modern wireless communication systems, the power amplifier of a transmitter of a radio is typically operated in the non-linear region to increase efficiency of the transmitter. As a result, the output of the power amplifier exhibits spectral regrowth unless some form of linearization is implemented. Digital Pre- distortion (DPD) is a well-known technique to linearize a power amplifier and thereby reduce spectral regrowth to an acceptable level. In order to implement a digital pre- distorter (DPD), a feedback path using a transmitter observation receiver (TOR) is provided to observe the transmitted signal.

FIG. 1 shows a known transceiver or radio that provides DPD and a TOR. A signal to be transmitted is received by a DPD 12, which pre-distorts the signal. A digital-to-analog D/A converter 14 converts the pre-distorted signal to an analog signal. The output of the D/A converter 14 is filtered by a filter 16 and amplified by a power amplifier 18. A coupler 20 couples a portion of the amplified signal to the TOR 25. The power amplifier output signal is also fed to a duplexer 22 which channels the output signal to an antenna 24. The TOR 25 down converts the input signal from the coupler 20 via mixer 26. The output of the mixer 26 is filtered by a filter 28 to produce the TOR output. The TOR output is converted to a digital signal by an analog-to-digital (A/D) converter 30. The output of the A/D converter 30 is fed to the DPD 12 which uses the output of the A/D converter 30 to pre-distort the signal to be transmitted.

The signal received by the antenna 24 from a distant radio such as a user equipment (UE) is coupled via the duplexer 22 to a receiver circuit 35. A low noise amplifier 32 amplifies the received signal. The amplified received signal is down converted by a mixer 34, filtered by a filter 36 and amplified by an amplifier 38. The output of the receiver circuit 35 is converted to a digital signal by a second A/D converter 40. The output of the A/D converter 40 is coupled to a receive signal processor 42 which processes the signal to extract information from the signal.

Thus, in a single transceiver having a single transmitter and a single receiver, two A/D converters are employed. In multi-band radios, multiple transceivers are used, each having its own pair of A/D converters. Further, each of the TOR path and the receiver circuit path may have I and Q channels, thereby doubling the number of A/Ds used in the radio. The use of so many A/D converters results in high radio power consumption, larger board space utilization, and larger heat fins for thermal management. Further, the cost of multiple A/D converters adds to the cost of the radio. These problems will become more pronounced with future 5^th generation radios that have increased numbers of antennas.

SUMMARY

The present disclosure advantageously provides a method and system for sharing an analog-to-digital (A/D) converter in a transceiver. According to one aspect, the disclosure provides a frequency division duplex (FDD) radio. The FDD radio includes at least one transceiver. Each transceiver has a digital pre-distorter and a receiver processor. Each transceiver also has a transmitter observation receiver (TOR) configured to produce a first analog signal at a first frequency. The first analog signal is converted to a first digital signal for transmission to the digital pre- distorter. A receiver circuit is configured to produce a second analog signal at a second frequency different from the first frequency. The second analog signal is converted to a second digital signal for transmission to the receiver processor. A shared wideband A/D converter is configured to, for each of the at least one transceiver: convert the first analog signal to the first digital signal ; and convert the second analog signal to the second digital signal .

According to this aspect, in some embodiments, the FDD radio further includes a duplexer configured to combine the first analog signal and the second analog signal from each of the at least one transceiver for input to the shared wideband A/D converter. In some embodiments, a TOR of at least one of the at least one transceiver includes a first mixer configured to down convert the transmit signal to the first frequency. In these embodiments, a receiver circuit of at least one of the at least one transceiver may include a second mixer configured to down convert the receive signal to the second frequency. In some embodiments, a difference between the first frequency and the second frequency is sufficient to enable simultaneous processing in the shared wideband A/D converter while maintaining separation of a signal to be processed by a digital pre-distorter, DPD, and a signal to be processed by the receiver processor of each of the at least one transceiver. In some embodiments, the receiver circuit of at least one of the at least one transceiver comprises: a first, low noise, amplifier having an output; a mixer coupled to the output of the low noise amplifier, the mixer configured to down-convert a received signal to produce a mixer output; a filter coupled to the mixer output and configured to filter the mixer output to produce a filter output; and a second amplifier coupled to the output of the filter and configured to amplify the filter output. In some embodiments, the TOR and the receiver circuit of at least one of the at least one transceiver form separate electrical paths sharing no common elements in the separate electrical paths. In these embodiments, the TOR path is configured to process the transmit signal coupled from an output of a power amplifier of the transmitter portion of the transceiver, and the receiver circuit path is configured to process the receive signal from an antenna of the transceiver.

According to another aspect, the disclosure provides a time division duplex (TDD) radio. The TDD radio includes at least one transceiver. Each transceiver has a transmitter observation receiver (TOR) forming a first continuously closed circuit electrical path configured to process a transmit signal coupled from an output of a power amplifier of a transmitter portion of the transceiver. The TOR has an output. A receiver circuit forms a second electrical path configured to process a receive signal from an antenna of the transceiver, the second electrical path having no elements in common with the first electrical path. The receiver circuit also has an output. A single shared A/D converter, the shared A/D converter receiving, for each transceiver, the TOR output and the receiver circuit output.

According to this aspect, in some embodiments, the TDD radio further includes a combiner to receive and combine the TOR outputs and receiver circuit outputs from the at least one transceiver for input to the single shared A/D converter. In other embodiments, the TDD radio has a switch coupled to the single shared A/D converter, the switch, in alternation, coupling the TOR outputs and the receiver circuit outputs of the at least one transceiver to the single shared A/D converter. In these embodiments, alternation of the coupling of the switch between the TOR output and the receiver circuit output of a transceiver of the at least one transceiver is synchronous with alternation of transmission and reception of the transceiver of the at least one transceiver. In some embodiments, the receiver circuit of the at least one transceiver includes a first mixer that is configured to down convert a receive signal to baseband. In some embodiments, the receiver circuit comprises: a first, low noise, amplifier having an output; a mixer coupled to the output of the low noise amplifier, the mixer configured to down-convert a received signal to produce a mixer output; a filter coupled to the mixer output and configured to filter the mixer output to produce a filter output; and a second amplifier coupled to the output of the filter and configured to amplify the filter output. In some embodiments, the first and second electrical paths are single paths not divided into I and Q channels.

According to yet another aspect, the disclosure provides a method in an FDD radio of processing a transmit signal to produce a first digital signal to be input to a digital pre-distorter and processing a receive signal to produce a second digital signal to be input to a receiver processing circuit. The method includes processing the transmit signal in a first processing path to produce a first analog output signal at a first frequency. The method further includes processing a receive signal in a second processing path to produce a second analog output signal at a second frequency different from the first frequency. The first and second analog output signals are combined. The method includes converting the combined first and second analog output signals to a digital output signal using a shared A/D converter. The digital output signal is provided to the digital pre-distortion unit of the transceiver. The digital output signal is also provided to the receiver processing circuit of the transceiver.

According to this aspect, in some embodiments, the combining includes band pass filtering the first analog output signal via a first band pass filter centered at the first frequency. The embodiments may further include band pass filtering the second analog output signal via a second band pass filter centered at the second frequency. In some embodiments, the first processing path is a single path and the second processing path is a single path. In some embodiments, the first processing path includes a mixer configured to down convert the transmit signal. In some embodiments, the second processing path includes a mixer configured to down convert the receive signal. In some embodiments, a difference between the first frequency and the second frequency is sufficient to enable simultaneous processing in the shared wideband A/D converter while maintaining separation of a signal to be processed by a digital pre-distorter, DPD, and a signal to be processed by a receiver processor. BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram of a known FDD single-transceiver radio;

FIG. 2 is a block diagram of an FDD single-transceiver radio constructed to share an A/D converter;

FIG. 3 is a block diagram of a TDD single-transceiver radio constructed to share an A/D converter;

FIG. 4 is a block diagram of a FDD multi-transceiver radio constructed to share an A/D converter;

FIG. 5 is a diagram of transmit and receive signals in an FDD system for multi- transceiver radios;

FIG. 6 is a diagram of transmit and receive signals in a TDD system for multi- transceiver radios; and

FIG. 7 is a flowchart of an exemplary process for sharing an A/D converter in an FDD radio.

DETAILED DESCRIPTION

Before describing in detail exemplary embodiments that are in accordance with the present disclosure, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to analog-to- digital conversion in radio transceivers. Accordingly, the system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

As used herein, relational terms, such as "first" and "second," "top" and "bottom," and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements.

Returning now to the drawing figures, where like reference designators refer to like elements, there is shown in FIG. 2 a transceiver 43 of a frequency division duplex (FDD) radio. In an FDD radio, transmission occurs at one frequency and reception occurs at another frequency so that transmission and reception occurs simultaneously but at different frequencies. As explained above, the FDD transceiver 43 has a transmitter observation receiver (TOR) 25 and a receiver circuit 35.

The TOR 25 provides feedback to the DPD 12 to control pre-distortion of the transmit signal to linearize the output of the power amplifier 18. As such, the TOR 25 down-converts using a first mixer 26 and filters the transmit signal via a filter 28. The first mixer 26 may down-convert the transmit signal to an intermediate frequency - in which case the filter 28 is a band pass filter - or may down-convert the transmit signal to base band - in which case the filter 28 is a low pass filter. The output of the filter 28 is fed to the DPD 12 via the duplexer 50 and the shared A/D converter 52.

The receiver circuit 35 down-converts the receive signal using a second mixer 34, filters the down converted signal using a filter 36 and amplifies the filtered signal using an amplifier 38. The second mixer 26 may down-convert the receive signal to an intermediate frequency - in which case the filter 36 is a band pass filter - or may down-convert the transmit signal to base band - in which case the filter 36 is a low pass filter. The output of the receiver circuit 35 is fed to a receiver processor 42 via the duplexer 50 and a shared wideband A/D converter 52. The receiver processor extracts information from the received signal. In some embodiments, the mixers 26 and 34 may down-convert the transmit and receive signals to different frequencies, respectively, to provide flexibility in the designs of the duplexer 50, A D converter 52, DPD 12 and receiver processor 42.

In some embodiments, the first analog output signal is band pass filtered by a first band pass filter 28 centered at the first frequency and the second analog output signal is band pass filtered by a second band pass filter 36 centered at the second frequency. In some embodiments, the first processing path 25 has a first mixer 26 to down-convert the transmit signal and the second processing path 35 has a second mixer 34 to down-convert the receive signal. In some embodiments, the difference between the first frequency and the second frequency is sufficient to enable simultaneous processing in the shared wideband A/D converter 52 while maintaining separation of a signal to be processed by a digital pre-distorter (DPD) 12, and a signal to be processed by a receiver processor 42.

Note that FIG. 2 shows two separate outputs from the A/D converter 52. In some embodiments, it is contemplated that the A/D converter 52 has a single output that is split, shared and routed to the DPD 12 and the receiver processor 42.

The FDD transceiver 43 for the radio of FIG. 2 uses many of the same components as used in the radio of FIG. 1 , except that in the transceiver of FIG. 2 the output of the TOR 25 and the output of the receiver circuit 35 are combined in a duplexer 50 and fed simultaneously to a single shared analog-to-digital (A/D) converter 52. The duplexer 50 receives signals from each of two input ports and channels the received signals to the output of the duplexer 50 while maintaining substantial isolation between the input ports. This architecture takes advantage of recent advances in high performance A/D converters that offer wide bandwidth and high linearity. The A/D converter 52 converts the signals received from the duplexer 50 to a digital signal having a sampling rate that is preferably at least twice the highest frequency of the bands of the input signals.

In the FDD transceiver 43 of the radio of FIG. 2, the down-converted transmitted signal is at a first frequency f 1 and the down-converted received signal is at a second frequency f2, where f 1 and f2 are sufficiently far apart to enable simultaneous processing in the A/D converter 52 while maintaining separation in the frequency domain. The output of the A/D converter 52 is fed to the DPD 12 and the receiver processor 42. By sharing the A/D converter 52 between the TOR output and the receiver circuit output, cost and utilized board space is reduced. Also, less power is consumed and less heat is produced. In order to be shared by both paths, the A/D converter 52 must have broad enough bandwidth to process the signal centered at f 1 and to process the signal centered at f2, simultaneously.

FIG. 3 is a block diagram of a time division duplex (TDD) radio having a transceiver 53 similar to the transceiver of FIG. 2 with at least the following differences. In the embodiment of FIG. 3, the transmit frequency is the same as the receive frequency. This frequency is time shared between transmission and reception. To achieve this, an isolator 54 and filter 55 pass the transmit signal to the antenna 24 during one time frame and pass the received signal from the antenna 24 to the receiver circuit 35 during another time frame. Another difference is that the duplexer 50 is replaced by the combiner 56. Note that the A/D converter 57 in the TDD radio need not be as broadband as the A/D converter 52 in the FDD radio.

Note also that the combiner 56 may be replaced by a switch that alternately couples the A/D converter 57 to the TOR output and the receiver circuit output. The alternation of the switch may be synchronous with alternation of transmission and reception of the transceiver. Thus, in the TDD transceiver 53 of FIG. 3, during a receive time frame the combiner 56 couples the receive signal from the receiver circuit 35 to the A/D converter 57 and during a transmit time frame the combiner 56 couples the transmit signal from the TOR 35 to the A/D converter 57.

Note also that in the configuration of FIG. 3 the TOR 25 forms a continuously closed circuit electrical path, and the TOR path and the receiver circuit path have no elements in common. Further, the first and second electrical paths are single paths that are not divided into I and Q channels, enabling use of a single shared A/D converter, rather than one for an I channel and one for a Q channel.

In some embodiments, the receiver circuit 35 down-converts the receive signal to baseband. Similarly, the TOR 25 may down convert the transmit signal to base band, depending on the structure of the DPD 12. In some embodiments, the receiver circuit 35 of the TDD transceiver may include a low noise amplifier 32 followed by a mixer 34 for down-conversion, a filter 36 and a second amplifier 28. The TOR 25 of the TDD transceiver may include a mixer 26 for down conversion and a filter 28. Note that the mixers 26 and 34 may, in some embodiments, down-convert the respective transmit and receive signals to different frequencies to provide flexibility in the design of downstream components.

FIG. 4 is a block diagram showing combining signals from a plurality of transceivers using a duplexer or combiner 58 and a shared A/D converter 60. Thus, the principles of sharing an A D converter according to embodiments described above can be applied to a radio having multiple transceivers 63 a, 63b, 63c, ...63m, referred to herein collectively as transceivers 63. Although four transceivers 63 are shown, fewer or more than four transceivers 63 can be implemented according to design objectives and the principles disclosed herein.

In the case of multiple transceiver implementation, each transceiver 63 has a DPD 12, DAC 14, filter 16, power amplifier 18, coupler 20, duplexer 22, and antenna 24. Each transceiver also has a TOR 25 and a receiver circuit 35. These are shown in FIG. 4 as DPD 12a, b, c, m (collectively referred to as DPD 12), DAC 14a, b, c, m (collectively referred to as DAC 14), filter 16a, b, c, m (collectively referred to as filter 16), power amplifier 18a, b, c, m (collectively referred to as power amplifier 18), coupler 20a ,b, c, m (collectively referred to as coupler 20), duplexer 22a, b, c, m (collectively referred to as duplexer 22), antenna 24a, b, c, m (collectively referred to as antenna 24), TOR 25a, b, c, m (collectively referred to as TOR 25) and receiver circuit 35a ,b, c, m (collectively referred to as receiver circuit 35). FIG. 4 shows that TOR 25 outputs and receiver circuit 35 outputs can be combined from a plurality of transceivers 63 and can be fed to a commonly shared A/D converter 60.

FIG. 4 shows multiple transceivers 63 of an FDD radio, which means that the transmit signal and the receive signal are at different frequencies, sufficiently separated to avoid substantial overlap of the spectra of the signals. The output of the shared A/D converter 60 is fed back to the DPDs 12 and is also fed to receive signal processors for each individual transceiver. For a TDD radio transceiver, an isolator and filter replaces the duplexer 22, and a different type of combiner replaces the combiner 58. The combiner of the FDD radio may be based on a multiplexer design since all inputs will be at different frequencies. For the TDD multi-transceiver radio, the combiner may be based on a Wilkinson combiner and multiplexer since some signals may be at the same frequency while others are not. Note that in FIG. 4 a single high performance wideband ADC 60 is provided to handle inputs from each of the plurality of transceivers 63.

The signals processed by the FDD multi-transceiver radio are also different from the signals processed by the TDD multi-transceiver radio. FIG. 5 shows the frequency spectrum of the transmit signals and receive signals for a FDD radio having four transceivers 63. For example, a first transceiver 63a may receive a receive signal 62a at frequency fl and transmit a transmit signal 64a at frequency f2. This is true also for the other transceivers 63b, 63c and 63m which receive receive signals 62b, 62c, and 62m (collectively referred to as receive signals 62), respectively, and which transmit transmit signals 64b, 64c and 64m (collectively referred to as transmit signals 64), respectively. Note that in FIG. 5, the spectra of the receive signal and the transmit signals alternate along the frequency axis. In alternative embodiments, a reordering of the spectra of the receive signal and the transmit signal may be implemented, according to a frequency use plan set forth in a design phase of the radio network.

FIG. 6 shows the frequency spectrum of the transmit and receive signals for a TDD radio having four TDD transceivers. In FIG. 6, for each of the four TDD transceivers, a receive and transmit signal overlap in frequency. Thus, for four TDD transceivers, there are four signals 66a, 66b, 66c and 66m (collectively referred to as signals 66), each signal 66 has overlapping transmit and receive signals that are separated in time rather than frequency.

FIG. 7 is a flowchart of an exemplary process of sharing an A/D converter 52 in an FDD radio transceiver 43. A transmit signal is processed in a first path 25 to produce a first analog output signal at a first frequency (block S100). In some embodiments, the first path is a single continuously closed circuit path. A receive signal is processed in a second path 35 to produce a second analog output signal at a second frequency (block SI 02). In some embodiments, the first and second signal paths have no elements in common. The first and second analog output signals are combined using a combiner or duplexer 50 (block S104). The combined first and second analog output signals are converted to a digital signal using a shared A/D converter 52 (block SI 06). The digital signal is provided to a DPD 12 of a transmit path of the transceiver 43 (block S108). The digital signal is also provided to a receiver processor 42 of a receive path of the transceiver 43 (block SI 10).

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims.

Claims

What is claimed is:

1. A frequency division duplex, FDD, radio, comprising:

at least one transceiver, each transceiver having:

a digital pre-distorter (12);

a receiver processor (42);

a transmitter observation receiver, TOR, (25) configured to produce a first analog signal at a first frequency to be converted to a first digital signal for transmission to the digital pre-distorter; and

a receiver circuit (35) configured to produce a second analog signal at a second frequency different from the first frequency to be converted to a second digital signal for transmission to the receiver processor; and

a shared wideband analog-to-digital, A/D, converter (60) configured to, for each of the at least one transceiver:

convert the first analog signal to the first digital signal ; and convert the second analog signal to the second digital signal .

2. The FDD radio of Claim 1 , further comprising a duplexer (50) configured to combine the first analog signal and the second analog signal from each of the at least one transceiver for input to the shared wideband A/D converter (60).

3. The FDD radio of Claim 1, wherein the TOR (25) of at least one of the at least one transceiver includes a first mixer (26) configured to down convert the transmit signal to the first frequency.

4. The FDD radio of Claim 3, wherein the receiver circuit (35) of at least one of the at least one transceiver includes a second mixer (34) configured to down convert the receive signal to the second frequency.

5. The FDD radio of Claim 1, wherein a difference between the first frequency and the second frequency is sufficient to enable simultaneous processing in the shared wideband A/D converter (60) while maintaining separation of a signal to be processed by the digital pre-distorter, DPD, (12) and a signal to be processed by the receiver processor (42) of each of the at least one transceiver.

6. The FDD radio of Claim 1, wherein the receiver circuit (35) of at least one of the at least one transceiver comprises:

a first, low noise, amplifier (32) having an output;

a mixer (34) coupled to the output of the low noise amplifier (32), the mixer (34) configured to down-convert a received signal to produce a mixer output;

a filter (36) coupled to the mixer output and configured to filter the mixer output to produce a filter output; and

a second amplifier (38) coupled to the output of the filter (36) and configured to amplify the filter output.

7. The FDD radio of Claim 1, wherein the TOR (25) and the receiver circuit (35) of at least one of the at least one transceiver form separate electrical paths sharing no common elements in the separate electrical paths, the TOR path being configured to process the transmit signal coupled from an output of a power amplifier (18) of the transmitter portion of the transceiver, and the receiver circuit path configured to process the receive signal from an antenna (24) of the transceiver.

8. A time division duplex, TDD, radio, comprising:

at least one transceiver, each transceiver having:

a transmitter observation receiver, TOR, (25) forming a first continuously closed circuit electrical path configured to process a transmit signal coupled from an output of a power amplifier (18) of a transmitter portion of the transceiver, the TOR (25) having an output;

a receiver circuit (35) forming a second electrical path configured to process a receive signal from an antenna (24) of the transceiver, the second electrical path having no elements in common with the first electrical path, the receiver circuit (35) having an output; a single shared analog-to-digital, A/D, converter (57), the shared A/D converter (57) receiving, for each transceiver, the TOR output and the receiver circuit output.

9. The TDD radio of Claim 8, further comprising a combiner (56) to receive and combine the TOR outputs and receiver circuit outputs from the at least one transceiver for input to the single shared A/D converter (57).

10. The TDD radio of Claim 8, further comprising a switch coupled to the single shared A/D converter (57), the switch, in alternation, coupling the TOR outputs and the receiver circuit outputs of the at least one transceiver to the single shared A/D converter (57).

11. The TDD radio of Claim 10, wherein alternation of the coupling of the switch between the TOR output and the receiver circuit output of a transceiver of the at least one transceiver is synchronous with alternation of transmission and reception of the transceiver of the at least one transceiver.

12. The TDD radio of Claim 8, wherein the receiver circuit (35) of the at least one transceiver includes a first mixer (34) configured to down convert a receive signal to baseband.

13. The TDD radio of Claim 8, wherein the receiver circuit (35) comprises: a first, low noise, amplifier (32) having an output;

a mixer (34) coupled to the output of the low noise amplifier (32), the mixer

(34) configured to down-convert a received signal to produce a mixer output;

14. The TDD radio of Claim 8, wherein the first and second electrical paths are single paths not divided into I and Q channels.

15. A method in a frequency division duplex, FDD, radio of processing a transmit signal to produce a first digital signal to be input to a digital pre-distorter and processing a receive signal to produce a second digital signal to be input to a receiver processing circuit, the method comprising:

processing the transmit signal in a first processing path to produce a first analog output signal at a first frequency (SI 00);

processing a receive signal in a second processing path to produce a second analog output signal at a second frequency different from the first frequency (SI 02); combining the first and second analog output signals (SI 04);

converting the combined first and second analog output signals to a digital output signal using a shared analog-to-digital, A/D, converter (60, S106);

providing the digital output signal to the digital pre-distortion unit (12, SI 08); and

providing the digital output signal to the receiver processing circuit (42,

S110).

16. The method of Claim 15, wherein the combining includes:

band pass filtering the first analog output signal via a first band pass filter centered at the first frequency; and

band pass filtering the second analog output signal via a second band pass filter centered at the second frequency.

17. The method of Claim 15, wherein the first processing path is a single path and the second processing path is a single path.

18. The method of Claim 15, wherein the first processing path includes a first mixer (26) configured to down convert the transmit signal.

19. The method of Claim 18, wherein the second processing path includes a second mixer (34) configured to down convert the receive signal.

20. The method of Claim 15, wherein a difference between the first frequency and the second frequency is sufficient to enable simultaneous processing in the shared wideband A/D converter (60) while maintaining separation of a signal to be processed by a digital pre-distorter, DPD, (12) and a signal to be processed by a receiver processor (42).