Design of Octave Tuning Range LC VCO With Ultralow KVCO Using Frequency-Dependent Implicit Capacitance Neutralization Technique

Abstract

This article presents a technique of frequency-dependent implicit capacitance neutralization (FD-ICN) among capacitor bank and varactors in LC voltage-controlled oscillator (VCO) to facilitate ultralow VCO gain ( $K_{\text {VCO}}$ ) across an octave frequency tuning range (TR). Series interconnect inductors are used between capacitor units to feature the inverse capacitance-frequency (C–f) relationship with varactors, thus yielding the proposed FD-ICN. A split 8-bit capacitor bank with centrosymmetric double-cross layout pattern is designed, enabling an enhanced FD-ICN through multiple capacitance equivalent iterations of the capacitor bank. The proposed FD-ICN technique is validated in a prototype of dual-mode electric-coupling VCO and fabricated in 130-nm CMOS process, exhibiting a measured frequency TR of 72.1% from 6.49 to 13.81 GHz with a $K_{\text {VCO}}$ of 7–73 MHz/V. The VCO shows a competitive phase noise (PN) and figures-of-merit in TR (FoM $\rm {_{T}}$ ) from −121.3 to −111.4 dBc/Hz and 197.4 to 201.7 dBc/Hz at 1-MHz offset across the whole TR.