Fully active and highly reliable combined ring voltage controlled CMOS oscillator

Leveraging two types of enhanced delay stages to form an oscillation loop, results in a highly reliable CMOS ring oscillator versus external interventions. The idea is investigated via symbolic delay calculations and the HSPICE circuit simulator while 0.18 μm CMOS is exploited. Based on two described inverters, three-ring oscillators are presented. The two ones use only one type of delay stage while the third is combined using two basic inverters and a single current-starved inverter. The basic type inverter is the fastest while is sensitive to power supply and temperature variations. On the other hand, the sensitivity of the current starved inverter is acceptable but this delay stage shows a large delay time, reducing oscillation frequency. This work tries to address this tradeoff between speed and sensitivity by proposing an oscillation loop. The delay times analysis and simulation results verify the robust performance of the proposed oscillator.