Calibrating a power amplifier such as in a remote unit in a wireless distribution system (WDS)

1. A communications system, comprising:

at least one remote unit configured to:

convert a plurality of downlink digital communications signals into a plurality of downlink radio frequency (RF) communications signals for distribution to client devices; and

receive a plurality of uplink RF communications signals from the client devices and convert the plurality of uplink RF communications signals into a plurality of uplink digital communications signals; and

a central unit configured to:

distribute the plurality of downlink digital communications signals to the at least one remote unit; and

receive the plurality of uplink digital communications signals from the at least one remote unit,

wherein the central unit comprises at least one electrical-to-optical (E/O) converter configured to convert the plurality of downlink digital communications signals into optical signals;

wherein at least one selected remote unit comprises a power amplifier calibration circuit, the power amplifier calibration circuit comprising:

a power amplifier comprising a signal input, a signal output, a first bias signal input, and a second bias signal input, wherein the power amplifier is configured to:

receive an input signal having a first power at the signal input;

receive a first bias signal at the first bias signal input;

receive a second bias signal at the second bias signal input;

amplify the input signal to generate an output signal having a second power higher than the first power at the signal output; and

control a first power amplifier performance parameter and a second power amplifier performance parameter in the output signal based on the first bias signal and the second bias signal; and

a control circuit configured to:

provide a plurality of bias signal combinations to the power amplifier, wherein each of the plurality of bias signal combinations comprises a respective first bias signal and a respective second bias signal to be provided to the first bias signal input and the second bias signal input of the power amplifier, respectively;

receive a plurality of performance indication signals comprising a plurality of measurements corresponding to the plurality of bias signal combinations, respectively, wherein each of the plurality of measurements comprises the first power amplifier performance parameter and the second power amplifier performance parameter;

rank the plurality of measurements based on a ranking criterion; and

determine a selected bias signal combination among the plurality of bias signal combinations corresponding to a selected ranked measurement among the plurality of measurements.

2. The communications system of claim 1 , wherein:

the first bias signal is represented by a first digital word; and

the second bias signal is represented by a second digital word.

3. The communications system of claim 1 , wherein the control circuit is further configured to control the power amplifier to operate based on the selected bias signal combination.

4. The communications system of claim 1 , wherein the power amplifier is further configured to:

receive a modulated broadband input signal at the signal input, wherein the modulated broadband input signal comprises a first signal in a first signal frequency and a second signal in a second signal frequency; and

generate a modulated broadband output signal at the signal output, wherein the modulated broadband output signal comprises the first signal and the second signal.

5. The communications system of claim 1 , wherein the power amplifier is further configured to:

receive the input signal from a signal generator communicatively coupled to the power amplifier; and

provide the output signal to a spectrum analyzer communicatively coupled to the power amplifier and the control circuit.

6. The communications system of claim 1 , wherein:

the first power amplifier performance parameter corresponds to a third-order intermodulation (IMD3) of the output signal;

the second power amplifier performance parameter corresponds to an adjacent channel power ratio (ACPR) of the output signal; and

the power amplifier is further configured to control the IMD3 and the ACPR of the output signal based on the first bias signal and the second bias signal.

7. An optical fiber-based wireless distribution system (WDS), comprising:

a plurality of cables including at least one optical communications medium; and

a plurality of remote units comprising optical-to-electrical (O/E) converters and configured to:

receive and convert a plurality of downlink digital communications signals into a plurality of downlink radio frequency (RF) communications signals for distribution to client devices; and

receive a plurality of uplink RF communications signals from the client devices and convert the plurality of uplink RF communications signals into a plurality of optical uplink digital communications signals;

wherein at least one selected remote unit among the plurality of remote units comprises a power amplifier calibration circuit, the power amplifier calibration circuit comprising:

a power amplifier comprising a signal input, a signal output, a first bias signal input, and a second bias signal input, wherein the power amplifier is configured to:

receive an input signal having a first power at the signal input;

receive a first bias signal at the first bias signal input;

receive a second bias signal at the second bias signal input;

amplify the input signal to generate an output signal having a second power higher than the first power at the signal output; and

control a first power amplifier performance parameter and a second power amplifier performance parameter in the output signal based on the first bias signal and the second bias signal; and

a control circuit configured to:

provide a plurality of bias signal combinations to the power amplifier, wherein each of the plurality of bias signal combinations comprises a respective first bias signal and a respective second bias signal to be provided to the first bias signal input and the second bias signal input of the power amplifier, respectively;

receive a plurality of performance indication signals comprising a plurality of measurements corresponding to the plurality of bias signal combinations, respectively, wherein each of the plurality of measurements comprises the first power amplifier performance parameter and the second power amplifier performance parameter;

rank the plurality of measurements based on a ranking criterion; and

determine a selected bias signal combination among the plurality of bias signal combinations corresponding to a selected ranked measurement among the plurality of measurements.

8. The WDS of claim 7 , wherein the control circuit is further configured to control operation of the at least one selected remote unit.

9. The WDS of claim 7 , wherein:

the first bias signal is represented by a first digital word; and

the second bias signal is represented by a second digital word.

10. The WDS of claim 7 , wherein the control circuit is further configured to control the power amplifier to operate based on the selected bias signal combination.

11. The WDS of claim 7 , wherein the power amplifier is further configured to:

receive a modulated broadband input signal at the signal input, wherein the modulated broadband input signal comprises a first signal in a first signal frequency and a second signal in a second signal frequency; and

generate a modulated broadband output signal at the signal output, wherein the modulated broadband output signal comprises the first signal and the second signal.

12. The WDS of claim 7 , wherein the power amplifier is further configured to:

receive the input signal from a signal generator communicatively coupled to the power amplifier; and

provide the output signal to a spectrum analyzer communicatively coupled to the power amplifier and the control circuit.

13. The WDS of claim 7 , wherein:

the first power amplifier performance parameter corresponds to a third-order intermodulation (IMD3) of the output signal;

the second power amplifier performance parameter corresponds to an adjacent channel power ratio (ACPR) of the output signal; and

the power amplifier is further configured to control the IMD3 and the ACPR of the output signal based on the first bias signal and the second bias signal.

14. A communications system, comprising:

a plurality of remote units comprising optical-to-electrical (O/E) converters and configured to:

convert a plurality of downlink digital communications signals into a plurality of downlink radio frequency (RF) communications signals; and

receive a plurality of uplink RF communications signals and convert the plurality of uplink RF communications signals into a plurality of uplink digital communications signals; and

a central unit configured to:

distribute the plurality of downlink digital communications signals to the plurality of remote units; and

receive the plurality of uplink digital communications signals from the plurality of remote units,

wherein the central unit comprises at least one electrical-to-optical converter configured to convert the plurality of downlink digital communications signals into optical signals;

wherein at least one selected remote unit among the plurality of remote units comprises a power amplifier calibration circuit, the power amplifier calibration circuit comprising:

a power amplifier comprising a signal output, a first bias signal input, and a second bias signal input, wherein the power amplifier is configured to:

receive an input signal having a first power;

receive a first bias signal at the first bias signal input;

receive a second bias signal at the second bias signal input;

amplify the input signal to generate an output signal having a second power higher than the first power at the signal output; and

control a first power amplifier performance parameter and a second power amplifier performance parameter in the output signal based on the first bias signal and the second bias signal; and

a control circuit configured to:

provide a plurality of bias signal combinations to the power amplifier, wherein each of the plurality of bias signal combinations comprises a respective first bias signal and a respective second bias signal to be provided to the first bias signal input and the second bias signal input of the power amplifier, respectively;

receive a plurality of performance indication signals comprising a plurality of measurements corresponding to the plurality of bias signal combinations, respectively, wherein each of the plurality of measurements comprises the first power amplifier performance parameter and the second power amplifier performance parameter;

rank the plurality of measurements based on a predefined ranking criterion; and

determine a selected bias signal combination among the plurality of bias signal combinations corresponding to a selected ranked measurement among the plurality of measurements.

15. The communications system of claim 14 , wherein the control circuit is further configured to control operation of the at least one selected remote unit.

16. The communications system of claim 14 , wherein:

the first bias signal is represented by a first digital word; and

the second bias signal is represented by a second digital word.

17. The communications system of claim 14 , wherein the power amplifier is further configured to:

receive a modulated broadband input signal at a signal input, wherein the modulated broadband input signal comprises a first signal in a first signal frequency and a second signal in a second signal frequency; and

generate a modulated broadband output signal at the signal output, wherein the modulated broadband output signal comprises the first signal and the second signal.

18. The communications system of claim 14 , wherein the power amplifier is further configured to:

receive the input signal from a signal generator communicatively coupled to the power amplifier; and

provide the output signal to a spectrum analyzer communicatively coupled to the power amplifier and the control circuit.

19. The communications system of claim 14 , wherein:

the first power amplifier performance parameter corresponds to a third-order intermodulation (IMD3) of the output signal;

the second power amplifier performance parameter corresponds to an adjacent channel power ratio (ACPR) of the output signal; and

the power amplifier is further configured to control the IMD3 and the ACPR of the output signal based on the first bias signal and the second bias signal.