Analysis and design of series combining transformers for integrated Doherty power amplifiers

In this paper, analysis and design of a series combining transformer based integrated Doherty PA is presented. A Z-parameter based model is used to optimize the series combining transformer(SCT) for Doherty operation. The proposed 2.4 GHz fully integrated Doherty Power Amplifier is fabricated in standard 90 nm CMOS technology and aimed for high linearity WLAN applications. The measurement results indicate that the PA shows efficiency enhancement at power back-off due to Doherty operation. The PA delivers 20.5 dBm output power with a peak drain efficiency of 30.9% (PAE 26.7%) by using 2 V supply voltage. The two stage Doherty PA has 16.6 dB small signal gain and 1 dB compression occurs at 17.5 dBm output power.