Crystal oscillator monitoring circuit

摘要

In an integrated circuit, a clock monitor circuit detects when an analog clock signal output by an on-chip crystal oscillator has stabilized. The clock monitor circuit uses an envelope follower circuit to monitor the envelope of the analog clock signal and compare the amplitude of the envelope with a predetermined amplitude value. When the predetermined value is reached and the envelope has remained steady for a predetermined time, an oscillator okay signal is generated. If an oscillator okay signal is not detected within another predetermined time, then an oscillator failure signal may be generated.

主权项

1. A clock monitoring circuit for detecting stable operation of a crystal oscillator, the clock monitoring circuit comprising:
an envelope follower circuit for receiving an analog output signal from the crystal oscillator and providing an envelope output signal; and signal processing circuitry, connected to the envelope follower circuit, for receiving the envelope output signal, comparing the envelope output signal with a reference signal over time using a comparator, and generating an output signal indicating stable operation of the crystal oscillator when the envelope output signal reaches and maintains a desired value for a preset period of time, wherein:
the comparator comprises an analog to digital converter (ADC) for producing digitized values of the received envelope output signal over time, andthe reference signal is a previous digitized value of the received envelope output signal.