Signal predistortion circuit configuration

A signal predistortion circuit configuration includes a digital predistortion circuit, a first transceiver, a first analog front-end (AFE) circuit, a second transceiver, and a second AFE circuit. The digital predistortion circuit outputs a first transmission signal according to first predistortion parameters and outputs a second transmission signal according to second predistortion parameters, and the digital predistortion circuit determines whether to adjust the first predistortion parameters according to a first reception signal and determines whether to adjust the second predistortion parameters according to a second reception signal. A transmitting circuit of the first transceiver, the first AFE circuit, and a receiving circuit of the second transceiver jointly generates the first reception signal according to the first transmission signal. A transmitting circuit of the second transceiver, the second AFE circuit, and a receiving circuit of the first transceiver jointly generates the second reception signal according to the second transmission signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a circuit configuration, especially to a signal predistortion circuit configuration.

2. Description of Related Art

Generally, a digital predistortion (DPD) circuit is used for cancelling the non-linear influence of an analog circuit (e.g., a power amplifier). For example,FIG.1shows a conventional wireless circuit configuration100including a digital signal processor (DSP)110, a DPD circuit120, a transmission-end (TX) path130, a front-end modulator (FEM)140, and a reception-end (RX) path150, wherein the TX path130includes a digital-to-analog converter (DAC)132, an upconverter134, and a power amplifier (PA)136, the RX path150includes a lower noise amplifier (LNA)152, a downconverter154, and an analog-to-digital converter (ADC)156, and the FEM140transmits/receives signals through an antenna in a communication mode. When determining digital predistortion parameters, the DPD circuit120outputs a predistortion signal according to a predetermined signal (e.g., a signal with a predetermined pattern) and the default setting of the digital predistortion parameters, then the predistortion signal is transmitted through the TX path130, the TX terminal (Tx) and the RX terminal (Rx) of the FEM140, and the RX path150and returns to the DPD circuit120, and then the DPD circuit120adjusts the digital predistortion parameters according to the difference between the returned predistortion signal and the predetermined signal, wherein the predetermined signal is generated by the DPD circuit120itself or comes from the DSP110. However, in order to optimize the circuit area, the distance between the TX path130and the RX path150is usually very short, and this cannot sufficiently insulate the TX path130from the RX path150. In light of the above, the signal coupling between the TX path130from the RX path150is serious, and this prevents the DPD circuit120from properly determining the digital predistortion parameters.

In order to prevent the aforementioned problem, a general solution is to set an additional reception path as shown inFIG.2. In comparison withFIG.1, the wireless circuit configuration200inFIG.2further includes a coupler210, a feedback circuit220, and a switch230. The feedback circuit220can be a circuit similar/equivalent to the LNA152and the downconverter154. When determining digital predistortion parameters, the DPD circuit120outputs a predistortion signal according to a predetermined signal and the default setting of the digital predistortion parameters, then the predistortion signal is transmitted through the TX path130, the TX terminal (Tx) of the FEM140, the coupler210, the feedback circuit220, the switch230, and the ADC156and returns to the DPD circuit120, and then the DPD circuit120adjusts the digital predistortion parameters according to the difference between the returned predistortion signal and the predetermined signal. Since the distance between the feedback circuit220and the TX path130is longer than the distance between the RX path150and the TX path130, the configuration ofFIG.2can prevent serious signal coupling between the TX path130from the RX path150when training digital predistortion parameters. However, the setting of the coupler210, the feedback circuit220, and the switch230requires additional pins and circuit areas, and this leads to a higher cost.

Another solution is to lower the requirements for a signal to interference ratio (SIR) in the configuration ofFIG.1and thereby lower the requirements for the insulation between the TX path130and the RX path150. However, this solution needs a high-end noise reduction algorithm and an advanced circuit design capability, and leads to a high cost and a lot of design difficulties.

SUMMARY OF THE INVENTION

A purpose of the present disclosure is to provide a signal predistortion circuit configuration capable of preventing the problem of the prior art.

An embodiment of the signal predistortion circuit configuration of the present disclosure includes a digital predistortion circuit, a first transmitting circuit, a first receiving circuit, a second transmitting circuit, a second receiving circuit, a first analog-front-end (AFE) circuit, and a second AFE circuit. The digital predistortion circuit is configured to output a first digital transmission signal according to at least one first parameter and output a second digital transmission signal according to at least one second parameter; and the digital predistortion circuit is further configured to determine whether to adjust the at least one first parameter according to a first digital reception signal and determine whether to adjust the at least one second parameter according to a second digital reception signal. The first transmitting circuit is configured to generate a first analog transmission signal according to the first digital transmission signal. The first receiving circuit is configured to generate the second digital reception signal according to a second analog reception signal and transmit the second digital reception signal to the digital predistortion circuit. The second transmitting circuit is configured to generate a second analog transmission signal according to the second digital transmission signal. The second receiving circuit is configured to generate the first digital reception according to a first analog reception signal and transmit the first digital reception signal to the digital predistortion circuit, wherein the minimum distance between the first transmitting circuit and the first receiving circuit is shorter than the minimum distance between the first transmitting circuit and the second receiving circuit, and the minimum distance between the second transmitting circuit and the second receiving circuit is shorter than the minimum distance between the second transmitting circuit and the first receiving circuit. The first AFE circuit is coupled between the first transmitting circuit and the second receiving circuit, and configured to generate the first analog reception signal according to the first analog transmission signal. The second AFE circuit is coupled between the second transmitting circuit and the first receiving circuit, and configured to generate the second analog reception signal according to the second analog transmission signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The specification discloses a signal predistortion circuit configuration capable of improving the insulation between a transmission-end (TX) path and a reception-end (RX) path at a very low cost when performing a digital predistortion (DPD) training process and thereby improving the effect of DPD.

FIG.3shows an embodiment of the signal predistortion circuit configuration of the present disclosure. The signal predistortion circuit configuration300ofFIG.3includes a digital signal processor (DSP)310, a DPD circuit320, a first transmitting circuit330, a first receiving circuit340, a second transmitting circuit350, a second receiving circuit360, a first analog-front-end (AFE) circuit370, and a second AFE circuit380. The whole function of the first transmitting circuit330, the first receiving circuit340, and the first AFE circuit370is similar/equivalent to the whole function of the second transmitting circuit350, the second receiving circuit360, and the second AFE circuit380.

Please refer toFIG.3. In an exemplary implementation, the signal predistortion circuit configuration300is applied to a multi-input multi-output (MIMO) wireless communication device (not shown inFIG.3). In this implementation, the first transmitting circuit330includes a first radio-frequency (RF) transmitting circuit (not shown inFIG.3); the first AFE circuit370is included in a first front-end modulator (FEM) (not shown inFIG.3), and the first AFE circuit370is configured to transmit a signal from a first TX terminal (Tx1) to a first RX terminal (Rx1) in a training mode and transmit/receive a signal through an antenna in a communication mode; and the first receiving circuit340includes a first RF receiving circuit (not shown inFIG.3). In addition, the second transmitting circuit350includes a second RF transmitting circuit (not shown inFIG.3); the second AFE circuit380is included in a second FEM (not shown inFIG.3), and the second AFE circuit380is configured to transmit a signal from a second TX terminal (Tx2) to a second RX terminal (Rx2) in the training mode and transmit/receive a signal through an antenna in the communication mode; and the second receiving circuit360includes a second RF receiving circuit (not shown in the figures). Furthermore, both the DSP circuit310and the DPD circuit320are included in a digital baseband circuit (not shown inFIG.3). The above-mentioned circuits not shown inFIG.3are well known in this technical field and fall beyond the scope of the present discussion, and their details are omitted here.

Please refer toFIG.3. In another exemplary implementation, the signal predistortion circuit configuration300is applied to an audio device (not shown inFIG.3). In this implementation, the first transmitting circuit330includes a first digital-to-analog converter (DAC) (not shown inFIG.3); the first AFE circuit370includes a first amplifier (not shown inFIG.3), and the first AFE circuit370is configured to transmit a signal from the Tx1to the Rx1in a training mode and transmit/receive a signal to/from an external device (e.g., a speaker or earphone) in a playback mode; and the first receiving circuit340includes a first analog-to-digital converter (ADC) (not shown inFIG.3). In addition, the second transmitting circuit350includes a second DAC (not shown inFIG.3); the second AFE circuit380includes a second amplifier (not shown inFIG.3), and the second AFE circuit380is configured to transmit a signal from the Tx2to the Rx2in the training mode and transmit/receive a signal to/from the external device in the playback mode; and the second receiving circuit360includes a second ADC (not shown inFIG.3). Furthermore, both the DSP circuit and the DPD circuit320are included in a digital audio circuit (not shown inFIG.3). The above-mentioned circuits not shown inFIG.3are well known in this technical field and fall beyond the scope of the present discussion, and their details are omitted here.

Please refer toFIG.3. The first transmitting circuit330is next to the first receiving circuit340, and the insulation between the two circuits is probably insufficient. The second transmitting circuit350is next to the second receiving circuit360, and the insulation between the two circuits is probably insufficient. In order to prevent the signal coupling caused by the insufficient insulation from affecting the effect of DPD, the signal predistortion circuit configuration300uses the first transmitting circuit330, the first AFE circuit370, and the second receiving circuit360as a signal loop for a first DPD training process, and uses the second transmitting circuit350, the second AFE circuit380, and the first receiving circuit340as another signal loop for a second DPD training process. Since the minimum distance between the first transmitting circuit330and the second receiving circuit360is much greater than the minimum distance between the first transmitting circuit330and the first receiving circuit340, the insulation between the first transmitting circuit330and the second receiving circuit360is relatively better, and thus the influence of the signal coupling on the effect of DPD can be reduced. Similarly, since the minimum distance between the second transmitting circuit350and the first receiving circuit340is much greater than the minimum distance between the second transmitting circuit350and the second receiving circuit360, the insulation between the second transmitting circuit350and the first receiving circuit340is relatively better, and thus the influence of the signal coupling on the effect of DPD can be reduced.

Please refer toFIG.3. When performing the first DPD training process, the DPD circuit320processes (e.g., distorts) a first original signal according to at least one first predistortion parameter and thereby outputs a first digital transmission signal (STXD1). Afterward, the first digital transmission signal is transmitted through the first transmitting circuit330, the Tx1of the first AFE circuit370, the Rx1of the first AFE circuit370, and the second receiving circuit360and then returns to the DPD circuit320; accordingly, the DPD circuit320can determine whether to adjust the at least one first predistortion parameter according to the difference between the returned signal (i.e., the first digital reception signal (SRXD1)) and the first original signal and thereby minimize the difference or ensure that the difference is small enough to fulfill the effect of DPD. In an exemplary implementation, the first original signal is generated by the DPD circuit320itself; in another exemplary implementation, the first original signal is generated by the DSP310. It should be noted that the first digital reception signal is under a first non-linear influence of the first transmitting circuit330, the first AFE circuit370, and the second receiving circuit360, and the digital predistortion circuit320adjusts the at least one first predistortion parameter to reduce/eliminate the first non-linear influence.

Please refer toFIG.3. When performing the second DPD training process, the DPD circuit320processes (e.g., distorts) a second original signal according to at least one second predistortion parameter and thereby outputs a second digital transmission signal (STXD2) Afterward, the second digital transmission signal is transmitted through the second transmitting circuit350, the Tx2of the second AFE circuit380, the Rx2of the second AFE circuit380, and the first receiving circuit340and then returns to the DPD circuit320; accordingly, the DPD circuit320can determine whether to adjust the at least one second predistortion parameter according to the difference between the returned signal (i.e., the second digital reception signal (SRXD2)) and the second original signal and thereby minimize the difference or ensure that the difference is small enough to fulfill the effect of DPD. In an exemplary implementation, the second original signal is generated by the DPD circuit320itself; in another exemplary implementation, the second original signal is generated by the DSP310. It should be noted that the second digital reception signal is under a second non-linear influence of the second transmitting circuit350, the second AFE circuit380, and the first receiving circuit340, and the digital predistortion circuit320adjusts the at least one second predistortion parameter to reduce/eliminate the second non-linear influence.

On the basis of the above description, the first transmitting circuit330is configured to generate a first analog transmission signal (STXA1) according to the first digital transmission signal (STXD1), and the first receiving circuit340is configured to generate the second digital reception signal (SRXD2) according to a second analog reception signal (SRXA2) and then transmit the second digital reception signal to the DPD circuit320. In addition, the second transmitting circuit350is configured to generate a second analog transmission signal (STXA2) according to the second digital transmission signal (STXD2), and the second receiving circuit360is configured to generate the first digital reception signal (SRXD1) according to a first analog reception signal (SRXA1) and then transmit the first digital reception signal to the DPD circuit320. The first AFE circuit370is coupled between the first transmitting circuit330and the second receiving circuit360, and configured to generate the first analog reception signal (SRXA1) according to the first analog transmission signal (STXA1) The second AFE circuit380is coupled between the second transmitting circuit350and the first receiving circuit340, and configured to generate the second analog reception signal (SRXA2) according to the second analog transmission signal (STXA2).

In an exemplary implementation, all of the first transmitting circuit330, the first receiving circuit340, the second transmitting circuit350, and the second receiving circuit360are included in an integrated circuit (i.e., the label “IC” inFIG.3) while the DPD circuit320can be included in the same integrated circuit or in another integrated circuit. In addition, the first AFE circuit370and the second AFE circuit380are set in a circuit board (e.g., a printed circuit board) (i.e., the label “PCB” inFIG.3), and they are not included in the above-mentioned integrated circuit. The first AFE circuit370is coupled to the second receiving circuit360through a first trace of the circuit board and a first connection interface (e.g., a pin or a solder ball) (not shown in the figures). The second AFE circuit380is coupled to the first receiving circuit340through a second trace of the circuit board and a second connection interface (e.g., a pin or a solder ball) (not shown in the figures).

FIG.4shows an embodiment of the first transmitting circuit330, the first receiving circuit340, the second transmitting circuit350, and the second receiving circuit360. The first transmitting circuit330includes a first DAC332and a first TX circuit334(e.g., a circuit including an upconverter and a power amplifier as shown inFIGS.1-2, wherein the power amplifier has a non-linear characteristic normally). The first DAC332is configured to generate a first conversion signal according to the first digital transmission signal (STXD1). The first TX circuit334is configured to generate the first analog transmission signal (STXA1) according to the first conversion signal. The first receiving circuit340includes a first RX circuit342(e.g., a circuit including a low noise amplifier and a downconverter as shown inFIGS.1-2) and a first ADC344. The first RX circuit342is configured to generate a second to-be-converted signal according to the second analog reception signal (SRXA2) The first ADC344is configured to generate the second digital reception signal (SRXD2) according to the second to-be-converted signal. Similarly, the second transmitting circuit350includes a second DAC352and a second TX circuit354(e.g., a circuit including an upconverter and a power amplifier as shown inFIGS.1-2, wherein the power amplifier has a non-linear characteristic normally) The second DAC352is configured to generate a second conversion signal according to the second digital transmission signal (STXD2) The second TX circuit354is configured to generate the second analog transmission signal (STXA2) according to the second conversion signal. The second receiving circuit360includes a second RX circuit362(e.g., a circuit including a low noise amplifier and a downconverter as shown inFIGS.1-2) and a second ADC364. The second receiving circuit362is configured to generate a first to-be-converted signal according to the first analog reception signal (SRXA1). The second ADC364is configured to generate the first digital reception signal (SRXD1) according to the first to-be-converted signal.

Please refer toFIG.4. In an exemplary implementation, the signal predistortion circuit configuration300is applied to a wireless communication device and further includes a first switch circuit410and a second switch circuit420. The first switch circuit410is coupled to the first AFE circuit370and the second receiving circuit360in a training mode, and is coupled to the first AFE circuit370and the first receiving circuit340in a communication mode. The second switch circuit420is coupled to the second AFE circuit380and the first receiving circuit340in the training mode, and is coupled to the second AFE circuit380and the second receiving circuit360in the communication mode. The DSP410is configured to receive a first communication signal through the first AFE circuit370, the first switch circuit410, and the first receiving circuit340and process the first communication signal in the communication mode. The DSP410is further configured to receive a second communication signal through the second AFE circuit380, the second switch circuit420, and the second receiving circuit360and process the second communication signal in the communication mode. The first communication signal is originated from a first external wireless device (not shown in the figures), and the second communication signal is originated from the first external wireless device or a second external wireless device (not shown in the figures). The first/second external wireless device wirelessly communicates with the wireless communication device to which the signal predistortion circuit configuration300is applied. To sum up, the signal reception path in the training mode is different from the signal reception path in the communication mode.

Please refer toFIG.4. The first digital reception signal (SRXD1) is under a first non-linear influence of the first transmitting circuit330, the first AFE circuit370, and the second receiving circuit360. The second digital reception signal (SRXD2) is under a second non-linear influence of the second transmitting circuit350, the second AFE circuit380, and the first receiving circuit340. In an exemplary implementation, the contribution made by the second receiving circuit360to the first non-linear influence is similar to the contribution made by the first receiving circuit340to the second non-linear influence; for example, the difference between the two contributions is lower than −10 decibel (dB). This small difference ensures that the parameter(s) determined in the training mode is applicable to the operation in the communication mode. In another exemplary implementation, the contribution made by the second receiving circuit360to the first non-linear influence is much lower than the contribution made by the first transmitting circuit330and the first AFE circuit370to the first non-linear influence; for example, the difference between the two contributions is greater than 10 dB. In addition, the contribution made by the first receiving circuit340to the second non-linear influence is much lower than the contribution made by the second transmitting circuit350and the second AFE circuit380to the second non-linear influence; for example, the difference between the two contributions is greater than 10 dB. In brief, in this implementation the contribution made by the transmitting circuit and the AFE circuit is dominant, and the contribution made by the receiving circuit is insignificant.

Please refer toFIG.3and the description ofFIGS.3-4. In an exemplary implementation, the signal reception path in the training mode is the same as the signal reception path in the communication mode; accordingly, the switch circuits (e.g., the first switch circuit410and the second switch circuit420ofFIG.4) operating according to the change of modes are not necessary, and the DSP310is configured to receive and process the first communication signal through the first AFE circuit370and the second receiving circuit360in the communication mode, and further configured to receive and process the second communication signal through the second AFE circuit380and the first receiving circuit340in the communication mode. Since those having ordinary skill in the art can appreciate the detail and modification of this implementation according to the embodiments and the exemplary implementations described in the preceding paragraphs, repeated and redundant description is omitted here.

It should be noted that in the communication mode the DPD circuit320can leave the at least one first predistortion parameter unchanged and/or leave the at least one second predistortion parameter unchanged; or in the communication mode the DPD circuit320can determine whether to adjust the at least one first predistortion parameter according to the first wireless communication signal, and/or determine whether to adjust the at least one second predistortion parameter according to the second wireless communication signal.

FIG.5shows another embodiment of the first transmitting circuit330, the first receiving circuit340, the second transmitting circuit350, and the second receiving circuit360. The first transmitting circuit330includes a first DAC502that is configured to generate the first analog transmission signal (STXA1) according to the first digital transmission signal (STXD1) The first receiving circuit340includes a first ADC504that is configured to generate the second digital reception signal (SRXD2) according to the second analog reception signal (SRXA2). The second transmitting circuit350includes a second DAC506that is configured to generate the second analog transmission signal (STXA2) according to the second digital transmission signal (STXD2). The second receiving circuit360includes a second ADC508that is configured to generate the first digital reception signal (SRXD1) according to the first analog reception signal (SRXA1).

Please refer toFIG.5. In an exemplary implementation, the signal predistortion circuit configuration300is applied to an audio device and further includes a first switch circuit510and a second switch circuit520. The first switch circuit510is coupled to the first AFE circuit370and the second receiving circuit360in a training mode, and coupled to the first AFE circuit370and the first receiving circuit340in a playback mode. The second switch circuit520is coupled to the second AFE circuit380and the first receiving circuit340in the training mode, and coupled to the second AFE circuit380and the second receiving circuit360in the playback mode. The DSP410is configured to receive and process a first audio signal (e.g., a first audio control signal from a speaker/earphone) through the first AFE circuit370, the first switch circuit510, and the first receiving circuit340in the playback mode. The DSP410is further configured to receive and process a second audio signal (e.g., a second audio control signal from a speaker/earphone) through the second AFE circuit380, the second switch circuit520, and the second receiving circuit360in the playback mode. In brief, the signal reception path in the training mode is different from the signal reception path in the playback mode. It should be noted that the limitations on the contributions made by the circuits to the first non-linear influence and the second non-linear influence described in the preceding paragraph are applicable to the above implementation. It should also be noted that in the playback mode the DPD circuit320can leave the at least one first predistortion parameter unchanged and/or leave the at least one second predistortion parameter unchanged; or in the playback mode the DPD circuit320can determine whether to adjust the at least one first predistortion parameter according to the first audio signal, and/or determine whether to adjust the at least one second predistortion parameter according to the second audio signal.

Please refer toFIG.3and the descriptions ofFIG.3andFIG.5. In an exemplary implementation, the signal reception path in the training mode is the same as the signal reception path in the playback mode; accordingly, the switch circuits (e.g., the first switch circuit510and the second switch circuit520ofFIG.5) operating according to the change of modes are not necessary, and the DSP310is configured to receive and process the first audio signal through the first AFE circuit370and the second receiving circuit360in the playback mode, and further configured to receive and process the second audio signal through the second AFE circuit380and the first receiving circuit340in the playback mode. Since those having ordinary skill in the art can appreciate the detail and modification of this implementation according to the embodiments and the exemplary implementations described in the preceding paragraphs, repeated and redundant description is omitted here.

It should be noted that people of ordinary skill in the art can selectively use some or all of the features of any embodiment in this specification or selectively use some or all of the features of multiple embodiments in this specification to implement the present invention as long as such implementation is practicable; in other words, the present invention can be carried out flexibly.

To sum up, the signal predistortion circuit configuration of the present disclosure can improve the insulation between a TX path and an RX path during the execution of DPD training, and therefore can improve the effect of DPD.