A low-phase-noise CMOS voltage-controlled oscillator (VCO) with zero-bias scheme and multi-stage filtering is presented. Sharing ground with fully integrated loop filter, the PMOS-only VCO achieves a zero-bias scheme, which prevents tuning line noise from disturbing VCO output common-mode voltage and hence minimizes phase noise caused by nonlinear C-V characteristic of varactors. Top-biased current source is optimized by multi-stage filtering to reduce 1/f flicker and thermal noise. Fabricated in TSMC 180 nm CMOS process, the proposed VCO exhibits a measured oscillation frequency of 0.85~1.45 GHz, with a phase noise of -121.8~-131.3 dBc/Hz @1MHz offset over the whole band. Power consumption is 3.8~6.3mW from a 1.8V supply.