High-Efficiency, Coupler-Based D-Band InP PA Stages With Output Power Above 16.4 dBm

This work presents a systematic design and comparison of D-band differential power amplifier (PA) stages in a 250-nm InP HBT technology, focusing on enhancing efficiency and stability. We introduce a horizontal-finger (HF) common-base layout that achieves robust stability without the performance trade-offs of conventional stabilization techniques. Two coupler-based output matching networks—a transformer-like coupler (TLC) and a straight-line coupler (SLC)—are implemented to evaluate the trade-offs between single-unit performance and power combining scalability. The TLC-based PA achieves a 33.6% collector efficiency (CE) with 17.5 dBm saturated output power (Psat) at 140 GHz, maintaining >25% CE across 120-150 GHz. The SLC-based PA demonstrates an alternative path optimized for series power combining. This work provides design insights into stable power cores and efficient combining topologies for future THz systems.