New measurement results and models for non-linear differential amplifier characterization

Previously, the author described a system that provides true differential and common-mode stimulus for CW and modulated RF signals, and presented results of non-linear operation of devices driven with such signals; they were compared with results for the same devices driven at the equivalent drive levels using a single-ended drive and calculating the differential response. Those devices showed no difference, in differential gain terms, whether measured with true-mode or single ended measurements. New results on limiting amplifiers demonstrate a substantial change in the differential gain compression when measured using a true differential mode drive. A theoretical model is developed which considers circuit topology differences and predicts which devices will have non-linear characteristics that change depending upon the test methods. Finally, some difficulties with error correction as applied to differential, non-linear circuits are discussed.