Efficiency enhancement using adaptive bias control for 60GHz power amplifier

Abstract

A single-stage 60GHz class-A bipolar power amplifier (PA) is fabricated in a BiCMOS 55nm technology. In order to enhance the power added efficiency (PAE) behavior of the PA, a bias control loop, based on direct power detection, is implemented in order to dynamically adjust the DC bias current of the PA according to its output power level. A power detector (PD) is connected directly at the output of the amplifier in order to track the envelope variation of its output signal. The employed PD has a dynamic range of more than 30dB, and a maximum power consumption of 0.8mW. Under constant bias conditions, the PA has a power gain of around 7dB, a maximum PAE of 16%, and an output compression point of around 7.5dBm while driving 25.8mA under 1.2V supply voltage. Under adaptive bias control, the mean value of the DC current is reduced down to 20.8mA, while maintaining high power gain, leading to a significant enhancement of the PAE over the linear input dynamic range of the PA. System level simulations show that the applied technique enhances the average PAE and DC power consumption by 18% without significant discrepancies on the EVM, ACPR, and power gain.