Browse Prior Art Database

SYNCHRONIZED IC MULTIVIBRATOR

IP.com Disclosure Number: IPCOM000024261D
Original Publication Date: 1980-Feb-29
Included in the Prior Art Database: 2004-Apr-02
Document File: 2 page(s) / 109K

Publishing Venue

Xerox Disclosure Journal

Abstract

Frequently it is desirable to synchronize two or more systems operating at different frequencies primarily to eliminate non-coherent noise. In those instances in which the oscillator to be synchronized is of the astable relaxation type (i.e., the oscillator will operate without being triggered and its timing interval is established by capacitive charging), present state of the art requires the synchronizing frequency to be limited to only frequencies higher than the synchronized frequency. The disadvantage of this requirement is that during loss of sync, the oscillator must free run at a frequency lower than the desired synchronized frequency and system performance may be degraded (e.g., due to increased power dissipation). Further-more, the synchronizing capture range must be sufficient to ensure sync lock for the worst case minimum value of the free-running frequency.

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CEROX DISCLOSURE JOURNAL

SYNCHRONIZED IC MULTIVIBRATOR Proposed Jeffrey E. Miller Classification

US. C1. 331/8 Int. CI. H03b 3/04

+V

TTTTTTTTTT

CD 40476

TI7

- 0

Frequently it is desirable to synchronize two or more systems operating at different frequencies primarily to eliminate non-coherent noise. In those instances in which the oscillator to be synchronized is of the astable relaxation type (i.e., the oscillator will operate without being triggered and its timing interval is established by capacitive charging), present state of the art requires the synchronizing frequency to be limited to only frequencies higher than the synchronized frequency. The disadvantage of this requirement is that during loss of sync, the oscillator must free run at a frequency lower than the desired synchronized frequency and system performance may be degraded (e.g., due to increased power dissipation). Further- more, the synchronizing capture range must be sufficient to ensure sync lock for the worst case minimum value of the free-running frequency.

The following disclosure presents a method of synchronizing a commonly used, integrated circuit relaxation oscillator, the CD 40478, configured in its astable mode despite the lack of provisions for such synchronization being intentionally designed into this IC by the manufacturer. In addition, this method permits the use of synchronization frequencies that can be either greater than, equal to or less than the free-running frequency, thus eliminating the disadvantage mentioned above.

This disclosure was implemented for use in display units of word processor systems to synchronize the high-voltage power supply DC-DC converter frequency to the horizontal scanning frequency thereby eliminating interference patterns from rolling through the display raster and eliminating flicker caused by a beat frequency from the unavoidable mixing of the two unsynchronized frequencies. The synchronization will thus result in a more visually appealing display.

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