A 386 GHz Injection-Lockable Push-Push Colpitts Oscillator in TS-InP-HBT with 1.3% Efficiency for Beam-Steered THz Arrays

Abstract Injection-locked terahertz oscillators enable coherent source arrays for beam steering, radar, and high-data-rate links. We present a compact, injection-lockable push-push Colpitts oscillator operating at 386 GHz, fabricated in a transferred-substrate indium phosphide heterojunction bipolar transistor (TS-InP-HBT) MMIC process. The circuit implements single-sided emitter injection at the fundamental f 0 together with a 50 Ω symmetry termination on the opposite emitter and no input matching network, while the Colpitts divider/phase shift is realized with distributed coupled-line sections for reproducible sub-THz behavior. A two-finger HBT core is used to raise transconductance while preserving parasitics compatible with the coupled-line feedback. Design and verification employ harmonic-balance/transient co-simulation with post-layout EM back-annotation of the feedback, injection feed, and transitions; measurements are performed on-wafer. The active core occupies 0.2 mm 2 and delivers −1.3 dBm at 386 GHz with 1.3% DC-to-RF efficiency. Under subharmonic injection (P inj ≈ −2.4 dBm at f 0 ), the 2f 0 output synchronizes to the injected reference and achieves a locked span of ≈3.10 GHz. Within this range, the measured single-sideband (SSB) phase noise at 100 MHz offset is ≈8 dB lower than in the free-running condition, reflecting the oscillator’s tracking of the cleaner injected tone. These results demonstrate that emitter-injection with symmetry termination, combined with EM-aware co-design of the distributed Colpitts network, achieves wide locking bandwidth and spectral cleaning in a footprint suited for dense, coherent THz arrays with potential for on-chip antenna integration.