A 42-62 GHz Transformer-Based Broadband mm-Wave InP PA with Second-Harmonic Waveform Engineering and Enhanced Linearity

Indium phosphide (InP) heterojunction bipolar transistors (HBTs) with f-{t}/f-{max} of 350/675 GHz are studied and explored for a linear, high efficiency and broadband power amplifiers (PAs) at mm-wave frequencies. Unlike the conventional transmission-like-based design, this article presents a compact, broadband transformer-based power combining and impedance matching using the waveform engineering approach. We present, for the first time, mm-wave (40-60 GHz) InP topologies incorporating the following: 1) on-chip transformer for broadband, efficient and compact impedance matching and power combining; 2) synthesis of optimal second-harmonic impedance through transformer center tap to achieve high-efficiency differential PA operation; and 3) biasing techniques to reduce AM-PM distortion for linearity enhancement. This work reports a transformer-based push-pull InP PA in 0.25~mu text{m} technology across 42-62 GHz demonstrating a peak power added efficiency (PAE) of 39.5% and peak P-{text{sat}} of 20.6 dBm. The PA supports 4 GHz bandwidth at 52 GHz with an EVM of -22.9 dB and an adjacent channel leakage ratio (ACLR) of -32 dBc for an 8 Gb/s QPSK signal at 13.3 dBm average output power. This work presents one of the highest efficiency with wide bandwidth and highest linearity mm-wave PAs in integrated technology.