A coupled two-stage ring oscillator

Modeling, analysis and test results of a fabricated coupled two-stage ring oscillator are presented in this paper. The oscillator consists of two two-stage ring oscillators which are coupled to each other and oscillate with the same frequency, but with 45 degrees phase difference resulting in two sets of quadrature outputs. It has been proven analytically that the coupled ring oscillator has an inherent capability of oscillating with frequencies as high as 1.96 times that of a single three-stage ring. A coupled two-stage ring oscillator, fabricated in CMOS 0.18 /spl mu/m technology, is described. This VCO has frequency tuning range of 2.5 - 9 GHz for a 1.8 V power supply voltage.