ANALYSIS OF THE CONDITIONS OF OCCURRENCE AND SUPPRESSION OF LATERAL VIBRATIONS IN MICROWAVE POWER FETS

Lateral instability is inherent in power transistors structures, consisting of several simple transistors connected in parallel. The large number of transistor elements complicates the analysis of such instability. The introduction of suppressing resistors makes it possible to prevent the occurrence of lateral oscillations, however there are no unambiguous criteria for achieving stability this way. The matter is further complicated by the fact that transistor exhibits nonlinear operation in a typical amplifier stage, and the operating conditions in many cases correspond to a relatively wide range of frequencies. In this paper, we present an analysis of lateral instability of a power amplifier stage, created on a basis of modern GaN field-effect transistor (FET). We had designed all dies and circuits for this FET. The main feature of the analysis is that we carried it out in the time domain, which made possible to estimate the stability of the stage not only under the excitation power pulse, but also after the end of the pulse. Our approach makes it possible to assess the stability of the amplifier between the excitation pulses, which is very important from the operational point of view. We calculated the estimates of operational stability and stability factor using a simplified transistor model, with the multi-element model reduced to a two-element model. Nevertheless, the results of the estimates retain their significance in real conditions, when the introduction of suppressing resistors creates a significant margin of stability, including the actual operating frequency band of the stage. To date, the data we have obtained after the manufacture of the samples only partially confirms the calculated estimates, due to the complexity of managing the experimental studies. However, there are no recorded results, which deny our estimates for the model.