CMOS transformer-based uneven Doherty power amplifier for WLAN applications

This paper reports a fully integrated Doherty power amplifier in standard 90 nm CMOS technology for 2.4 GHz WLAN applications. An asymmetrical series combining transformer is used as the Doherty combiner to enhance the efficiency at power back-off. The two-stage uneven Doherty PA has 18 dB gain and produces 26.3 dBm saturated output power, with a peak power added efficiency (PAE) of 33% by using 2 V supply voltage. The PAE at 6 dB back-off is still as high as 25.1%. The PA is tested with 54 Mbps WLAN 802.11g signal and meets the stringent EVM and spectral mask requirements at 19.3 dBm average output power with a PAE of 22.9% with no need of predistortion. Then, an open loop digital predistortion is applied to further improve the linearity. The PA satisfies WLAN requirements at 20.2 dBm average output power with a PAE of 24.7% with predistortion.