Apparatus and method to generate a 50% duty cycle clock in a single-ended crystal oscillator

Abstract

A clock generator includes an active oscillator portion that generates an oscillating signal having a frequency determined by a resonator, such as a crystal or other type of resonator. A filter or delay module filters or delays the oscillating signal to generate a second oscillating signal that has a DC component that matches that of the original oscillating signal. A comparator then compares the original oscillating signal with the filtered or delayed oscillating signal to determine the amplitude cross points. In other words, the comparator determines where the amplitude of the original oscillating signal crosses that of the filtered or delayed oscillating signal, and generates a square wave pulse at the amplitude cross points. Since both compared signals have a common DC component then the amplitude cross points will be equally separated in time, which produces an output oscillating signal with a 50% duty cycle.