Biasing circuits for voltage controlled GSM power amplifiers

In GSM phones, voltage controlled power amplifiers are used to vary the output power. Inaccuracies in output power levels are predominantly caused by drift in PA gain over temperature and input power. In this paper, we present biasing circuits that implement an inherently accurate gain control curve. These circuits are based on temperature stabilised V/I-converters and current mirrors. Applying current driven biasing of the first RF-stage reduces the input power dependency of the gain. Measurements show an order of magnitude less drift in PA gain over temperature variations and about a factor five smaller drift over input power variations. The proposed circuits relax the dynamic range and stability requirements on the power control loop and they help make phone output power calibrations redundant.