Design of a 1.2 V Low Phase Noise 1.6 GHz CMOS Buffered Quadrature Output VCO with Automatic Amplitude Control

This paper presents the design of a low phase noise 1.6 GHz CMOS buffered quadrature output VCO with automatic amplitude control. It is operated with a supply voltage of 1.2 V and dissipates a current of less than 10 mA. It is capable of delivering quadrature locked signals with almost constant amplitude in the range from 1.22 GHz to 1.95 GHz with a phase noise response of less than -115 dBc at an offset of 1 MHz from the carrier. The effect of the automatic amplitude control is shown to improve phase noise at high oscillation frequencies and its noise has a negligible effect on phase noise response, even at low offset frequencies from the carrier. Design guidelines for reducing both the loop noise and the AM-PM conversion factors of the oscillator are also given.