Multi-level digital adaptive pa bias for microwave radios

A power amplifier circuit, comprising:

• a power amplifier for amplifying a transmission signal, the transmission signal having a time-varying envelope;
• an envelope detector that produces a time-varying signal indicative of an amplitude of the envelope of the transmission signal;
• a plurality of comparators for comparing the time-varying signal to a plurality of distinct threshold voltages, each comparator having a first input receiving the time-varying signal and a second input receiving a respective threshold voltage of the plurality of distinct threshold voltages;
• a plurality of switches, each switch having a first terminal and a second terminal, each switch being controlled by an output of a respective comparator of the plurality of comparators to form a conductive channel between the first terminal and the second terminal when the time-varying signal indicative of the amplitude of the envelope of the transmission signal exceeds the respective threshold voltage for the respective comparator;
• a plurality of digital-to-analog converters (DACs) providing a plurality of bias voltages, wherein the first terminal of each switch of the plurality of switches is coupled to a respective DAC of the plurality of DACs;
• a summing device having inputs coupled to the second terminals of each of the plurality of switches to produce an output bias voltage that is at least a sum of bias voltages from each of the second terminals of the plurality of switches, wherein the output bias voltage is applied to bias the power amplifier;
• memory storing a plurality of sets of distinct threshold voltages, each set of the plurality of sets of distinct threshold voltages corresponding to a modulation type;
• and
• one or more processors configured to:
• detect a change in modulation type of the transmission signal;
• and
• reprogram the plurality of distinct threshold voltages to a different set of distinct threshold voltages, of the plurality of sets of distinct threshold voltages, based on the change in the modulation type of the transmission signal.