Large signal comparative modeling and characterization of GaAlAs HEMT, GaAs MESFET and Si bipolar transistor microwave oscillators

Solid state oscillators are widely used in microwave equipment and their spectral purity specifications are among the hardest to satisfy. The reason is that microwave active devices, because of their reduced sizes, inherently exhibit large low frequency excess noise, which is up-converted by the device nonlinearities in baseband noise near the carrier. In this work, three different types of microwave active devices are considered: Si bipolar transistor, GaAs Schottky field-effect transistor (MESFET) and GaAlAs-GaAs field-effect transistor (HEMT). To understand such a behavior, the authors have had to realize first a non-linear modeling of each active device with the aim to simulate the non-linear behavior of the oscillator, the later being built with each device. Thus, it is possible to predict, output power, 1dB compression point and noise up-conversion. This work allows comparison of different types of active devices commonly used in microwave oscillators