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System with Multiple Clocks each Using a Crystal Controlled Oscillator and Interconnected with other Oscillators to Form a Phase Locked Loop if a Crystal Fails

IP.com Disclosure Number: IPCOM000037494D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Boerstler, DW: AUTHOR

Abstract

Some data processing systems have a large number of identical components that each require a circuit called a clock that produces timing pulses. The clocks must run at closely similar rates but they are not required to be synchronized. An improved clock has a semiconductor oscillator with a frequency determining network that is controlled by either a crystal or a reactance that can be varied by means of a control voltage. The control voltage is developed by a circuit that compares the oscillator frequency with a reference frequency. Such a circuit is called a phase locked loop because the frequency and phase of the oscillator are locked to the reference frequency and phase. A circuit that generates a frequency from a reference frequency is commonly called a frequency synthesizer.

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System with Multiple Clocks each Using a Crystal Controlled Oscillator and Interconnected with other Oscillators to Form a Phase Locked Loop if a Crystal Fails

Some data processing systems have a large number of identical components that each require a circuit called a clock that produces timing pulses. The clocks must run at closely similar rates but they are not required to be synchronized. An improved clock has a semiconductor oscillator with a frequency determining network that is controlled by either a crystal or a reactance that can be varied by means of a control voltage. The control voltage is developed by a circuit that compares the oscillator frequency with a reference frequency. Such a circuit is called a phase locked loop because the frequency and phase of the oscillator are locked to the reference frequency and phase. A circuit that generates a frequency from a reference frequency is commonly called a frequency synthesizer.

Commonly, the crystal controlled oscillator is more expensive than the frequency synthesizer. In this system, a few of the circuits are connected as crystal oscillators and the rest are connected as frequency synthesizers. Each crystal oscillator is connected to provide a clock signal to its associated component and to provide a reference signal to a suitable number of frequency synthesizers.

In another application for this circuit, the crystal oscillators are interconnected to receive, but initially not to use, the output of one...