Frequency doubler with duty cycle monitor means

Abstract

A frequency doubler for receiving an input clock signal and generating an output signal at twice the input signal frequency and having fifty percent duty cycle. The input signal is received by a tapped delay line and transmitted from a predetermined tap thereof to a first input of an EXCLUSIVE OR gate. The second input of the EXCLUSIVE OR gate receives the undelayed input clock signal and generates the output clock signal in response to performing an EXCLUSIVE OR operation on the delayed and undelayed signals. The duty cycle of the output signal is monitored via a comparator in combination with logic circuitry. The output of the comparator is connected to the up/down input of a digital counter which is clocked once for each cycle of the input signal, and generates a digital count value in response thereto. In the event that the monitored duty cycle is less than fifty percent, the comparator generates an up count signal for incrementing the digital counter. In the event that the duty cycle is greater than fifty percent, the comparator generates a down count signal for decrementing the counter. The counter output is connected to a decoder circuit for decoding the digital count valve and generating a signal to enable one of the taps of the delay line, thereby compensating for drift in the components comprising the delay line, and maintaining the output signal at fifty percent duty cycle.