A Current-Reused VCO With Inductive-Transformer Feedback Technique

This article presents a low phase noise (PN) voltage-controlled oscillator (VCO) based on a current-reused structure with inductive-transformer feedback (ITF) technique. With the proposed topology, the drain-to-gate voltage gain (
$A_{v}$
), negative conductance (
$G_{m}$
), loaded-
$\mathbf {\mathit {Q}}$
, and the impulse sensitivity function (ISF) are improved, thus better PN. Besides, the ITF can improve the transistors’ switch synchronization by eliminating the waveform offset of the waveforms at the gate nodes, leading to smaller amplitude errors. As a proof of concept, the VCO is designed and fabricated in a 65-nm CMOS process consuming 0.25 mm
²
die area and 7.7 mW from the 1.2-V supply. The measurement results exhibit a PN of −115.35 dBc/Hz at 1 MHz offset when the oscillation frequency is 6.85 GHz, and a tuning range of 29.9% varying from 6.27 to 8.47 GHz. The VCO achieves a figure-of-merit (FoM) of −183.11 dBc/Hz and a −192.6-dBc/Hz tuning range included FoM(FoM
_T
).