A bias-circuit-noise cancellation VCO was designed and fabricated in a 0.18 μm CMOS process. By inserting a strobe circuit between the bias circuit and the VCO core, the noise voltage from the bias circuit could be low-pass filtered. Analyses showed that the corner frequency of the low-pass filter was dependent on the turn-on resistance and turn-off resistance of the strobe circuit as well as the duty cycle of the switching clock. Measurement results showed that with the assistance of the strobe circuit, the near-end phase noise of the VCO was reduced by 20 dB approximately, exhibiting a significant suppression for flicker noise from the bias circuit.