Phase noise in a back-gate biased low-voltage VCO

The phase noise in an ultra low-power and low-voltage CMOS voltage controlled oscillator (VCO) has been measured and modelled for supply voltage V_DD from 1.8 V down to 80 mV with various body bias voltages V_BS. The VCO is a fully integrated ring oscillator designed in a 0.18 μm CMOS technology. In this design, the frequency can be controlled by V_BS. The effects of scaling V_DD together with the effect of V_BS on the phase noise are examined experimentally and theoretically. It has been observed that the phase noise at V_DD >0.5 V is dominated by the upconverted 1/f noise. But the low frequency noise disappears when V_DD decreases below 0.5 V. Application of forward body bias voltages from 0 to 0.6 V also provides a practical method to suppress the low frequency noise being upconverted to phase noise.