New modeling results for non-linear differential amplifier behavior, including two-tone TOI response

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, which were compared with the same devices driven at the same levels using single-ended drive and calculating the differential response. Some devices showed no difference in the differential gain terms whether measured with true-mode or single ended measurements, and some showed substantial change in the differential gain compression when measured using true differential mode drive. A theoretical model was proposed which considers circuit topology differences to predict which devices will have non-linear characteristics that change depending upon the test methods. A new modeling approach is presented here which confirms these predictions, clearly identifies the underlying causes for the non-linear differential behavior and extends the results to modulated measurements such as TOI. Using these models, new effects of non-ideal measurements are discovered, pointing to yet more complex requirements for true-mode non-linear test.