Power amplifier bias synchronization
A power amplifier system includes a nonlinear power amplifier that receives a predistorted input signal. A receiver receives an output signal from the power amplifier and provides an observed signal. A bias controller provides a delayed dynamic bias signal to the power amplifier wherein the bias signal delay is dynamic and is a function of the observed signal for synchronizing the predistorted input signal with the dynamic bias signal. A method is also described that alternately adjusts predistortion delays and bias signal delays as a function of observed signals.
1. A power amplifier system comprising:
a nonlinear power amplifier that receives a predistorted input signal;
a linear receiver that receives an output signal from the nonlinear power amplifier and provides an observed signal;
a bias controller that provides a delayed dynamic bias signal to the nonlinear power amplifier wherein the delayed dynamic bias signal is variable and is a function of the observed signal for synchronizing the predistorted input signal with the delayed dynamic bias signal.
2. The power amplifier system of claim 1 and further comprising a frequency selective power meter that provides a signal representative of the quality of the observed signal for selected frequencies.
3. The power amplifier system of claim 1 and further comprising:
a predistortion gain block that provides the predistorted input signal; and
an adaptive predistortion controller coupled to the linear receiver for receiving the observed signal and control the gain of the predistortion gain block.
4. The power amplifier system of claim 3 wherein the predistortion controller determines a predistortion variable delay to synchronize the gain of the predistortion gain block with an input signal, and wherein the predistortion controller provides feedback synchronization information to the bias controller for determining the delayed dynamic bias signal.
5. The power amplifier system of claim 4 wherein the predistortion variable delay is determined as a function of minimizing a phase difference between the input signal and the observed signal.
6. The power amplifier system of claim 5 wherein the delayed dynamic bias signal is determined to maximize a cross correlation of the magnitudes of the input signal and the observed signal.
7. The power amplifier system of claim 6 wherein the delayed dynamic bias signal is determined after the predistortion variable delay.
8. The power amplifier system of claim 1 and further comprising:
a predistortion gain block that provides the predistorted input signal;
an adaptive predistortion controller coupled to the linear receiver for receiving the observed signal and control the gain of the predistortion gain block; and
a multichannel synchronizer coupled to the linear receiver and the predistorted input signal for dynamically determining a predistortion variable delay and the delayed dynamic bias signal.
9. The power amplifier of claim 8 wherein the predistortion variable delay is determined as a function of minimizing a phase difference between the predistorted input signal and the observed signal and wherein the delayed dynamic bias signal is determined to maximize the cross correlation of the magnitude of the predistorted input signal and the observed signal.
10. A power amplifier system comprising:
a nonlinear power amplifier;
means for predistorting an input signal to linearize an output of the power amplifier;
means for providing a variably delayed dynamic bias signal to the nonlinear power amplifier.
11. The power amplifier system of claim 10 wherein the variably delayed dynamic bias signal is delayed as a function of an observed output signal from the nonlinear power amplifier.
12. The power amplifier system of claim 10 wherein the means for predistorting the input signal to linearize the output of the power amplifier comprises a variable predistortion control delay.
13. The power amplifier system of claim 10 wherein the variably delayed dynamic bias signal is a function of early-late amplitude cross correlation observation.
14. The power amplifier system of claim 10 wherein the variably delayed dynamic bias signal is a function of frequency selective power measurements.
15. The power amplifier system of claim 10 wherein the dynamic bias signal delay is a function of observed synchronization of input signal predistortion as an input signal predistortion is held constant.
16. A method comprising:
adjusting a first variable delay for an adaptive predistortion controller for a predistortion gain block for predistorting an input signal for amplification by a nonlinear amplifier while holding a dynamic bias signal for the nonlinear amplifier constant;
upon synchronization of the adaptive predistortion controller, holding the first variable delay constant and activating modulation of the dynamic bias signal; and
adjusting a second variable delay corresponding to the dynamic bias signal until the adaptive predistortion controller is resynchronized.
17. The method of claim 16 and further comprising upon synchronization of the adaptive predistortion controller, sending the first variable delay to a bias controller for use in adjusting the second variable delay.
18. The method of claim 16 wherein adjustment of the second variable delay is done in a direction corresponding to a comparison between an input signal and an observed output of the nonlinear power amplifier.
19. The method of claim 18 wherein the first variable delay is determined as a function of an early-late amplitude cross correlation observation between the input signal and the observed output of the nonlinear power amplifier.
20. The method of claim 16 wherein the adjusted second variable delay is held constant and the first variable delay is adjusted again.