A 27.6-dBm Four-Stack X-Band CMOS Power Amplifier With Supply-Voltage-Scalable Multipower-Mode Operation

This article presents an X-band CMOS power amplifier (PA) employing a four-stack topology with supply-voltage-scalable multipower-mode operation, targeting highly integrated beamforming systems that require both high output power and high efficiency across a wide output power range. In conventional CMOS PAs, the already-low supply voltage headroom severely limits the practical range of supply voltage scaling, making multipower-mode operation ineffective. The supply voltage scaling range is theoretically bounded by the per-transistor reliability constraint at the upper limit and the saturation condition at the lower limit, with both bounds scaling proportionally with the number of stacked transistors. Consequently, the proposed four-stack topology raises the allowable supply voltage to 4.0 V and provides a scaling range of approximately 3.48 V—significantly wider than that achievable with conventional two- or three-stack designs—enabling meaningful multipower-mode operation verified through node voltage simulations. By dynamically adjusting the supply voltage according to the required output power level, the proposed PA shifts the peak efficiency point without additional amplifier paths or switching networks, making it particularly suitable for compact beamforming channel integration. The PA is designed and fabricated in a 65-nm RF CMOS process. At 10 GHz, the PA achieves a P_1dB of 27.3 dBm and a saturation output power (P ${}_{\mathbf {SAT}}$ ) of 27.6 dBm—the highest output power reported for CMOS X-band PAs to date. Furthermore, compared to the high-power mode, the proposed multipower-mode operation improves average PAE by 4.3%, 7.5%, and 6.6% at 2-, 6-, and 10-dB output back-off points, respectively. These results validate that the proposed architecture simultaneously achieves record output power and enhanced back-off efficiency within a compact core area of 0.218 mm².