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Clock Recovery from Asynchronous Signals with Minimum Jitter

IP.com Disclosure Number: IPCOM000106878D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Camp Jr, WO: AUTHOR

Abstract

This article describes a clock recovery circuit that reduces clock phase variation when deriving a clock signal from a data signal.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Clock Recovery from Asynchronous Signals with Minimum Jitter

      This article describes a clock recovery circuit that reduces
clock phase variation when deriving a clock signal from a data
signal.

      The signal out of a radio demodulator is a sequence of signals
representing data that must be sampled at optimum times by means of a
clock signal derived from the data signal.  Most clock recovery
methods use either an oscillator at the data rate that is phase
locked to the data signal or a bandpass filter with its center
frequency at the data rate.  For instance, a 1 Mb/s data rate would
generate a 1 MHz clock with either a 1 MHz oscillator or bandpass
filter centered at 1 MHz.  Both methods represent a filter at the
data rate.

      The problem with such recovery methods is that the spectral
energy at 1 MHz for 1 Mb/s data signals is extremely small, in
theory, zero.  Thus, the filter must have a large-enough bandwidth
(or large loop bandwidth in the phase-locked loop approach) in order
to receive enough spectral energy to create the signal at 1 MHz.
This makes the phase of the signal vary in response to changing
patterns in the data signal.

      In this method, my clock recovery circuit consists of a
bandpass filter at a frequency equal to one-half of the data rate,
followed by a frequency doubler to create the clock signal at the
data rate, a gain block and limiter to make the clock signal uniform
regardless of data pattern, and a phase shifter to compensate for
componen...