Wide frequency range CMOS relaxation oscillator with variable hysteresis

摘要

A voltage controlled oscillator (VCO) which may be adjusted to provide oscillatory signals for a wide range of frequencies includes a relaxation oscillator in which a ramp signal is compared to a reference threshold which exhibits hysteresis. The frequency of the oscillator is changed by varying the hysteresis range of the threshold level and by changing the rate at which the ramp is generated. At higher frequencies, the signal processing delay through the comparator is a factor in determining the frequency of the signal produced by the oscillator. Current sources internal to the oscillator are controlled by a reference potential that is generated from an externally supplied band-gap reference potential. The VCO is used in a phase-locked loop which includes a charge pump circuit that accumulates charge on a capacitor responsive to limited-width pulses applied to a current source which is controlled by the reference potential generated in the VCO.