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Clock Recovery Circuit

IP.com Disclosure Number: IPCOM000090765D
Original Publication Date: 1969-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Esteban, DJ: AUTHOR

Abstract

This multilevel clock recovery circuit consists of a delay circuit, two digitally controlled full-wave rectifiers, a synchronization sign slope anticipation circuit, and a comparator circuit. Prediction of the sign of the slope of the synchronization signal avoids inverting the opposite synchronization signals, half of them being of the opposite sign. If not done, synchronization can be lost with the set patterns of the opposite synchronization slope. Only three operational amplifiers are needed, the comparator included, and no logic circuits are used to select true synchronization information. This circuit can be extended from two levels to four levels or eight levels with the use of a full-wave rectifier, two levels of full-wave rectifiers or four levels of full-wave rectifiers.

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Clock Recovery Circuit

This multilevel clock recovery circuit consists of a delay circuit, two digitally controlled full-wave rectifiers, a synchronization sign slope anticipation circuit, and a comparator circuit. Prediction of the sign of the slope of the synchronization signal avoids inverting the opposite synchronization signals, half of them being of the opposite sign. If not done, synchronization can be lost with the set patterns of the opposite synchronization slope. Only three operational amplifiers are needed, the comparator included, and no logic circuits are used to select true synchronization information. This circuit can be extended from two levels to four levels or eight levels with the use of a full-wave rectifier, two levels of full-wave rectifiers or four levels of full-wave rectifiers.

Recognition of the synchronization pulses allows to refixing the phase of the clock. These pulses are determined by comparison of the signal at a sampling instant with the signal at the preceding sampling instant, delay tau. On an oscillographic representation, the superposition of such signals gives sharp areas around the sampling instant. Because of the aspect of these areas, they are termed eyes. On the drawing, there is an eye area for data A and an eye area for data B. The principle of the full-wave rectification and shift is shown in the drawing. In order to detect all the possible arrangements in the eye, which are equal to the square of the number of level...