0.4V CMOS based low power voltage controlled ring oscillator for medical applications

In this paper, a two-stage voltage controlled ring oscillator has been designed, analyzed and verified by simulations with 0.18μm technology. This voltage controlled ring oscillator uses partial positive feedback in its each stage, which allows the circuit to operate with only two stages. It only consumes 4.98mW in its central frequency of 1.90 GHz using a 1.5V power supply. Further, voltage controlled ring oscillator circuit is designed with bulk-drain connected load in the sub-threshold region. By connecting the bulk and drain terminals of PMOS, it exhibits a more linear IDS-VDS characteristic and therefore it can be conveniently used as loads for sub-threshold circuits. By using this load, VCO can be operated at low supply voltage. Further, it has been depicted from the analysis and simulation results that the power consumption of the VCO has been reduced to a great extent. The maximum power consumption of the circuit is 3.2nW using 0.4V power supply and oscillating frequency is 170kHZ.These characteristics are highly attractive for its use in ultra low power applications particularly in medical applications.