Analysis and design of an optimally coupled 5-GHz quadrature LC oscillator

A 5-GHz quadrature LC oscillator has been realized, in which the two LC stages are coupled with phase shifters. Analysis on the behavioral level shows that an N-stage LC oscillator is optimally coupled when each stage is connected with phase shifters providing /spl plusmn/180/spl deg//N phase shift. Simulation of the 5-GHz two-stage quadrature LC oscillator reveals a 4.3-dB reduction in phase noise compared to a quadrature LC oscillator without phase shifters. Measurements of the 5-GHz quadrature LC oscillator, made in a 30-GHz f/sub T/ process, show a phase noise lower than -113 dBc/Hz, with a resonator quality factor of only 4 and an oscillator core power dissipation of 21.2 mW.