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 plusmn 5% from -40 to 125degC over process variations. The 1.25 GHz oscillator in 0.13 mum CMOS draws 3.4 mA and has a phase noise of -88 dBc/Hz at 1MHz offset.