Implementation and Measurement of a DSP-Based Adaptive Bias Technique for a 135 GHz Power Amplifier

This study presents the experimental validation of an adaptive bias technique for a D-band power amplifier operating in the back-off region. The optimal bias function as a function of the input power was derived by measuring the power amplifier characteristics under various gate bias conditions at 135 GHz. A dynamically varying bias voltage according to the envelope of the input signal was generated using an arbitrary waveform generator. The bias function based on the actual device input power was implemented by compensating for losses in the measurement path. The measurement results demonstrate that the average power-added efficiency under the adaptive bias condition closely follows the maximum power-added efficiency envelope, confirming that the derived bias function accurately tracks the optimal operating point. Satisfactory signal quality was maintained in the verification using 16-quadrature amplitude modulation signals.