The benefit of GaN characteristics over LDMOS for linearity improvement using drain modulation in power amplifier system

This paper reports that significant linearity improvement can be obtained in gallium nitride (GaN) RF power amplifiers (RFPAs) in comparison to laterally diffused metal oxide semiconductor (LDMOS) RFPAs through the use of a modulated drain supply. It is shown that the gain characteristic of a GaN RFPA has significant variation with the drain bias voltage and this results in a 10-20 dB reduction in intermodulation (IM) levels. The LDMOS RFPA was measured and the result showed that the gain of LDMOS did not change substantially with drain bias voltage. As a consequence, when the LDMOS RFPA is measured using modulated drain bias, the IM levels showed only a much smaller improvement. These results appear to indicate that GaN devices have an important advantage over LDMOS in linear RFPA applications.