A Process and Temperature Compensated Two-Stage Ring Oscillator

Local positive feedback in a delay element enables a ring oscillator with only two stages to oscillate and produce quadrature clocks. Routh-Hurwitz's criterion is applied to prove that such a structure can oscillate. An internally generated power supply from a constant-gm bias keeps the free running frequency to within ±5% from -40 to 125°C over process variations. The 1.25GHz oscillator in 0.13μm CMOS draws 3.4mA and has a phase noise of -88dBc/Hz at 1MHz offset.