Impact of the input baseband impedance on the intermodulation distortion and linearizability of RF power transistors

Abstract

Nonlinearities in Radio Frequency Power Transistors can be attributed to mechanisms such as non-linear transconductances and nonlinear capacitances at the device terminals. In this paper, we extend the work in by Ladhani et al to include the impact of the nonlinear gate-source capacitance in a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and discuss its contribution (along with the gate baseband impedance) to the amplifier’s intermodulation distortion and linearizability. Measured results show that for a 140W (P1dB (1dB Compression Point)) Class AB LDMOS (Laterally Diffused Metal Oxide Semiconductor Field Effect Transistor) PA, an optimized gate baseband impedance provides 6dB improvement in corrected ACPR (Adjacent Channel Power Ratio) and 7dB improvement in corrected Alt-1 (First Adjacent Channel Power Ratio) at 7dB backoff from peak power using a 4-Carrier WCDMA (Wideband Code Division Multiple Access) signal.