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Synchronizer for Multiphase Clocks

IP.com Disclosure Number: IPCOM000100908D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 84K

Publishing Venue

IBM

Related People

Nathanson, B: AUTHOR

Abstract

This circuit synchronizes several multiphase clock generators. Ordinarily, even if all generators derive their output from the same oscillator, and are turned on at the same time, their outputs will not necessarily be in phase because the generators may have different internal states at power-up. It is not always possible to force the generators to a known initial state. This circuit guarantees that, regardless of initial state or when the generators are powered on, an n-phase clock generator will attain synchronism within n cycles.

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Synchronizer for Multiphase Clocks

       This circuit synchronizes several multiphase clock
generators.  Ordinarily, even if all generators derive their output
from the same oscillator, and are turned on at the same time, their
outputs will not necessarily be in phase because the generators may
have different internal states at power-up.  It is not always
possible to force the generators to a known initial state.  This
circuit guarantees that, regardless of initial state or when the
generators are powered on, an n-phase clock generator will attain
synchronism within n cycles.

      The circuit operates as follows.  For illustration we use a
four- phase active-low clock whose phases are designated T0, T1, T2,
T3, and let there be two clock generators to be synchronized, G0 and
G1.  The extension to three or more clock generators is described
subsequently.

      Choose one phase of one clock generator arbitrarily to be a
reference.  The other clocks will be synchronized to this.  For
illustration we choose phase T0 of generator G0.

      Figure 1 shows the circuit, and Figure 2 the resulting
waveforms.

      Each clock generator, other than the reference, gets its
oscillator input from a synchronizer.  When the reference clock is
active, the synchronizer will "skip a beat" of its oscillator output
if it detects a phase mismatch.  Each skipped beat moves the
out-of-phase clock one phase closer to the reference clock until the
phases coincide....