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Self Checking Oscillator Failure Detector

IP.com Disclosure Number: IPCOM000086632D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Curlander, PJ: AUTHOR

Abstract

An oscillator O is defined as having failed when two consecutive clock pulses are missing. This oscillator failure detector uses three monostable multivibrators (SS1, SS2, SS3) to check the oscillator. The pulse width or active time of each monostable multivibrator is approximately two and one-half clock or pulse periods.

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Self Checking Oscillator Failure Detector

An oscillator O is defined as having failed when two consecutive clock pulses are missing. This oscillator failure detector uses three monostable multivibrators (SS1, SS2, SS3) to check the oscillator. The pulse width or active time of each monostable multivibrator is approximately two and one-half clock or pulse periods.

SS1 becomes active every time there is a clock pulse detected and it is not already in the active state, such as shown in the waveform SS1. SS2 becomes active only when SS1 is active and a clock pulse is received. Similarly, SS3 becomes active only when both SS1 and SS2 are simultaneously active and a clock pulse is received. This set of rules results in the illustrated signal waveforms.

Oscillator failure is detected by any one of the four D-type latches 10 being set to the active condition. In this regard, AND circuit A4 checks the condition that SS1 has reverted to the inactive state when both SS2 and SS3 are inactive. Similarly, AND circuit A5 sets its associated D-type latch when SS1 and SS3 are simultaneously inactive when SS2 is inactive, i.e., SS2 going inactive is a clock to the D-type latch. AND circuit A6 checks the condition that SS1 and SS2 are both inactive when SS3 reverts to the inactive state. Finally, the bottom D-type latch is set to the active condition whenever a clock pulse C occurs, and all three monostable multivibrators are in the active condition. That is, if any of the monostab...