Predistortion Linearisation of Amplifiers for UHF Mobile Radio

Predistortion introduced to correct for amplifier nonlinearity is a technique well known in principle, but its application has been restricted to relatively expensive high power amplifier installations. Small cells for FM and TDMA mobile communications systems require linear transmitter amplifiers with power outputs of about 100 mW to 1 W. This paper describes the theory and evaluation of a 1 GHz medium power amplifier whose performance has been enhanced by a simple predistorter circuit. Tests over a temperature range of -10°C to 52°C show that a significant improvement in linearity can be maintained for all amplifier drive levels up to a maximum drive level by means of a simple diode and resistor predistorter circuit that includes an external bias which needs to respond to temperature but not to drive level.