400 GHz HBT Differential Amplifier Using Unbalanced Feed Networks

A terahertz differential eight-stage amplifier fabricated using state-of-the-art 125 nm double-heterojunction bipolar transistors (DHBT) is presented. The four-port unit-cell chain is designed for optimum forward differential gain with no even and odd-mode reverse gains. Unbalanced single-ended feed networks are added to preserve the amplifier gain without inducing oscillations. The proposed feed scheme is validated by a stable amplifier operation in 325-to-450 GHz range with the peak gain of 22 dB at 375 GHz.