Start-up time of CMOS oscillators

This paper describes the evolution of signals in CMOS inverter-based oscillators during start-up. The time constant characterizing the exponential increase of the oscillation amplitude is determined by a small-signal analysis of the resonant circuit, and the dependence of this time constant on circuit parameters is examined. Calculation of the initial value of currents and voltages generated when power is applied to the inverter is explained. Oscillator start-up under various conditions is analyzed and different types of resonators are taken into account. The total oscillator starting time can be determined from the present work. Results of experimental work carried out on the oscillator of the microprocessor MC68HC04P3 with ceramic and quartz resonators agree well with the calculated values. Oscillograms illustrate how the start-up occurs.