A quadrature output voltage controlled ring oscillator based on three-stage sub-feedback loops

This paper presents a general ring oscillator circuit topology for high speed operation, multiphase output and wide range tuning. The topology use sub-feedback inverters to construct fast loop for long chain ring oscillator to achieve high speed. The operating frequency of the ring oscillator is directly proportional to the transconductance (G(m)) of sub-feedback inverters which can be controlled with an external voltage. Both single-ended and differential controlled voltage and inverter stages can be used. A quadrature output ring oscillator based on three-stage sub-feedback loops is designed and fabricated in a 0.5 mu m CMOS process for a 1.25GHz clock recovery application. The circuit operates from 400MHz up to 2GHz, and consumes 3mW at 1.25GHz with 3.3V power supply.