Broadband Harmonic-Assisted Power and Efficiency Enhancement in a 174–232-GHz SiGe Voltage-Controlled Oscillator

This article presents a wideband sub-THz Colpitts voltage-controlled oscillator (VCO) with a novel harmonic-assisted technique to enhance power efficiency across a large tuning range. We first show how the proposed oscillator architecture operates compared to conventional Colpitts oscillators and present the efficiency enhancement techniques. Furthermore, we demonstrate a harmonic-based adjustment of power efficiency using a variable impedance at the device embedding network. We also evaluate the effect of the harmonic-assisted operation on the phase noise of the oscillator through the comparison of simulation and measurement results. The circuit is fabricated in a 55-nm SiGe BiCMOS technology occupying a compact area of 0.29 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. A 174–232-GHz oscillation bandwidth (28.6%) is achieved with a peak output power of −0.4 dBm and 2.9% peak dc-to-RF efficiency while the power variation across the tuning range is 5.8 dB and a 41-GHz 3-dB bandwidth of output power is achieved. The best-measured phase noise is −100 dBc/Hz at the 10-MHz offset.