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Browse Prior Art Database

Integrated Digital Stuck-Clock Detector

IP.com Disclosure Number: IPCOM000100067D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Peterson, MJ: AUTHOR [+2]

Abstract

The figure illustrates circuitry for an integrated digital stuck-clock detector. The circuit detects when a clock coming onto a chip becomes stuck in a high or low state.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 84% of the total text.

Integrated Digital Stuck-Clock Detector

       The figure illustrates circuitry for an integrated
digital stuck-clock detector.  The circuit detects when a clock
coming onto a chip becomes stuck in a high or low state.

      A system clock is divided down to obtain a square wave less
than half of a minimum ring oscillator frequency (in this case, 2 MHz
is used as an example).  A ring oscillator is designed with a tight
frequency tolerance.  The detector comprises two sampling circuits
clocked by the ring oscillator.  Outputs of these two circuits are
ORed together to form a "clock stuck" signal.  This signal is then
used to override the output of any sequential logic using the system
clock.

      The two sampling circuits monitor the system clock.  If the top
"AND" circuit samples 10 consecutive ones, it assumes the clock is
stuck at a one.  Likewise, if the bottom "OR" circuit samples 10
consecutive zeroes, it assumes the clock is stuck at a zero.

      The minimum ring oscillator frequency is greater than twice the
divided system clock frequency to guarantee a sample of each half of
the divided system clock square wave.  If the ratio is exactly 2:1, a
sample is always the same half of the square wave, and a
stuck-at-zero or -one results.

      At the maximum ring oscillator frequency, enough samples are
required to sample both halves of the square wave.  With a 2 MHz
square wave and a 20 MHz maximum ring oscillator frequency, six
samples...