Dual-Mode CMOS Power Amplifier Based on Load-Impedance Modulation

Abstract

This letter presents a dual-mode CMOS power amplifier (PA) that has an improved efficiency using load-impedance modulation in the low-power mode (LPM) and a fully differential operation in the high-power mode (HPM). For the LPM, the transistor in the negative path of the differential pair is turned ON, as a switch, to appropriately modulate the load impedance for the transistor in the positive path using the output balun. An external switch is deployed to turn $V_{\text {DD}}$ OFF for the negative path. In order to verify the proposed concept, a dual-mode CMOS PA IC was designed using a bulk CMOS process and an off-chip output balun, and it was evaluated using the 920-MHz narrow-band Internet of Things signal with a bandwidth of 200 kHz and a peak-to-average power ratio of 5.7 dB. For the HPM, the implemented PA exhibited a gain of 24.1 dB, a power-added efficiency (PAE) of 44.3%, and an adjacent channel leakage power ratio (ACLR) of −33.9 dBc at an average output power of 27.7 dBm. For the LPM, a gain of 19.3 dB, a PAE of 37.7%, and an ACLR of −34.9 dBc were obtained at an average output power of 21.7 dBm.