A 20.5-dBm $X$ -Band Power Amplifier With a 1.2-V Supply in 65-nm CMOS Technology

In this letter, we present an X-band power amplifier (PA) which achieves a saturated output power (P_sat) of 20.5 dBm under a 1.2-V supply in 65-nm CMOS. Considering the relatively low breakdown voltage of the 65-nm device, we adopted a differential configuration with a triple-well cascode in which the n-well of the cascode device was biased with a resistor. Also, the PA adopted an on-chip 1:2 transformer to provide a low output impedance at the drain, and a series RC feedback was employed to enhance the stability and the gain bandwidth (BW) as well. The measured 3-dB BW of the PA covered the whole X-band and supported an output 1-dB gain compression point (OP1dB) of 15.2 dBm. A peak power-added efficiency of 24.6% with a gain of 24.4 dB at 9 GHz was recorded. The core of the PA occupies only 0.48 mm².