A Broadband Doherty-like Load-Modulated Balanced Amplifier with an Optimized Impedance Transformation Ratio in InGaP/GaAs HBT Process for Handset applications

This study presents a design methodology for implementing broadband load modulated balanced amplifier (LMBA) for handset applications. It is evaluated which architecture, Doherty-like LMBA (DL-LMBA) or pseudo-Doherty LMBA (PD-LMBA), is more suitable for InGaP/GaAs HBT power amplifier (PA). The impedance transformation ratio (ITR) is optimized through an analysis of correlation between the coupler impedance (Z0) and matching network. A prototype LMBA attains measured saturation power (PSAT), collector efficiency (CE), and 6 dB output power back-off (OBO) CE of over 33.2 dBm, 45.2%, and 42.0%, respectively, in the range of 3.2-5.0 GHz. The LMBA is also evaluated by 5G NR FR1 100 MHz QPSK CP-OFDM with 9.5 dB peak-to-average power ratio (PAPR), achieving 26.6 dBm average output power (Pavg) with 37.7% average CE (CEavg) at adjacent channel leakage ratio (ACLR) of -33 dBc.