A 144- μW Phase-Interval Balanced RVCO With 142% Tuning Range and 218.2-dBc/Hz FoM TA

This paper presents a phase-interval balanced ring voltage-controlled oscillator (RVCO) with ultra-low power and ultra-wide frequency tuning range (FTR), for wearable or implanted brain-computer sensors. An approximate phase-interval error analysis model is developed to quantify the phase imbalance introduced by switched capacitors in phase-combined RVCOs. Based on this model, digitally controlled switched capacitors are incorporated into the low-power RVCO core to significantly expand the FTR while reducing phase-interval imbalance. An enhanced time-window phase combiner (E-TWPC) is further proposed to improve tolerance to residual phase-interval errors and mitigate phase noise degradation over a wide operating range. Prototyped in 65-nm CMOS, the proposed oscillator consumes only 16-144~μWand achieves an FTR of 440MHz-2.6GHz (142%) under 4-bit digital control. This RVCO maintains comparable phase noise performance to existing RVCOs, while occupying a compact area of0.00057~mm², achieving aFoMTAof 218.2dBc/Hz at 1MHz offset.