Power Amplifier With Load Impedance Sensing Incorporated Into the Output Matching Network

This paper presents a radio-frequency power amplifier (RF PA) with load impedance sensing circuitry incorporated into its output matching network (OMN), but without insertion of series elements into the RF transmission path, limiting its impact on performance. The approach is based on multi-port reflectometry, such as can be used in sampled-line impedance sensors, generalized to an arbitrary linear network and applied to the existing OMN of a PA. With the addition of samplers to the OMN, offline computation is performed to determine the complex reflection coefficient at a specified reference plane. The proof-of-concept class-AB harmonically-tuned sampled-OMN PA operating at 3 GHz demonstrates load reflection coefficient sensing within less than 4.6% error over the entire measured region of the Smith chart, i.e. up to 0.8 magnitude reflection coefficient, when the PA is driven with a 6-dBm CW signal. For a 2-tone input with 5-MHz tone spacing and 6-dBm average input power, sensing accuracy is within 16.3% for 80% of the measured loads.