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 uses sub-feedback inverters to construct a 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 μm CMOS process for a 1.25 GHz clock recovery application. The circuit operates from 400 MHz up to 2 GHz, and consumes 3 mW at 1.25 GHz with 3.3 V power supply