Switchless Dual-Power-Mode Fully Differential HBT Power Amplifier for Mobile Applications

This study proposes a switchless dual-power-mode (DPM) power amplifier (PA), which operates independently in high-powermode (HPM) and low-power mode (LPM) to improve the efficiency. The DPM PA optimizes the output impedances using bias control of the PA and the proposed bidirectional output matching structure with a transformer (TF) for each power mode with no switches for isolation between the LPM and the HPM with high passive efficiency. The proposed output structure realizes a high impedance in the nonoperating mode network to ensure that the operating mode network realizes the optimal impedance by utilizing bidirectional matching of the OFF characteristics of transistors and TF output for each mode. The differential DPM PA is implemented using a 2-
$\mu \mathrm {m}$
InGaP/GaAs heterojunction bipolar transistor (HBT) process on a nine-layer printed circuit board with low insertion loss to demonstrate the proposed structure. The HPM and LPM, operating independently, achieved the gains of 24–25.5 and 11.4–12.9 dB and the saturated output power of 34.2–34.8 and 23.2–23.5 dBm, with a peak power-added efficiency (PAE) of 44.4%–49% and 32%–34.4%, respectively, under a continuous-wave (CW) signal test of over 5.15–5.925 GHz. The proposed PA error vector magnitude (EVM) is tested with 160 MHz of a 64-quadrature amplitude modulator (QAM) signal and achieves the average output powers of 24.5 and 14 dBm (EVM = −32 dB) and a PAE of 10.5% and 10.1% for HPM and LPM with digital predistortion, respectively.