Dual positive feedback VCO with noise cancellation

A low phase noise voltage controlled oscillator (VCO) is proposed by employing two positive feedback loops. One of them is used to enhance the output signal swing of the VCO while the other cancels the noise of active devices to reduce the noise contribution of those devices to the phase noise of the VCO. The proposed VCO is fabricated in a 0.18 μm 1P6M CMOS process. The measurement result shows that the phase noise is 126.6 dBc/Hz at 1 MHz offset frequency from the oscillation frequency of 3.8 GHz while dissipating 5.1 mA from a 1.0 V supply voltage with a FOM of 191.1 dBc/Hz.