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Single Shot with Noise Immunity

IP.com Disclosure Number: IPCOM000092101D
Original Publication Date: 1968-Sep-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Ford, JW: AUTHOR

Abstract

Single-shot circuits of the type having a normally nonconductive input transistor, capacitively coupled to a normally conductive output transistor, are usually susceptible to noise disturbances on the power line. Conventionally, a single-shot circuit has input control terminal 10 feeding through a resistor R11 to the base of transistor T12 whose emitter is grounded. The collector of T12 is connected through resistor R13 to a power source. T12 is normally nonconducting. Transistor T14 has its emitter connected to ground and its collector connected through resistor R15 to the power source. T14 is rendered normally conductive by a base bias current source of resistor R16 and diode D17 between the source and the base of T14.

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Single Shot with Noise Immunity

Single-shot circuits of the type having a normally nonconductive input transistor, capacitively coupled to a normally conductive output transistor, are usually susceptible to noise disturbances on the power line. Conventionally, a single-shot circuit has input control terminal 10 feeding through a resistor R11 to the base of transistor T12 whose emitter is grounded. The collector of T12 is connected through resistor R13 to a power source. T12 is normally nonconducting. Transistor T14 has its emitter connected to ground and its collector connected through resistor R15 to the power source. T14 is rendered normally conductive by a base bias current source of resistor R16 and diode D17 between the source and the base of T14. Feedback resistor R18 is connected from the collector of T14 to the base of T12 and capacitor C19 connects the collector of T12 to the junction R16 and D17.

In operation, a positive signal at input 10 turns on T12 to drop its collector voltage. The voltage pulse through C19 and D17 turns off T14 and the resultant positive voltage at its collector feeds back through R18 to hold T12 conductive. This condition holds until C19 has discharged through R16 to a point in which the base current for T14 can feed through R16 and D17 to turn on T14. This starts restoration to the original conditions. Such a single-shot is susceptible to noise on the current supply for any negative noise spike can pass through R13 and C19 to th...