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Noise Immune High Gain Photodevice Amplifier

IP.com Disclosure Number: IPCOM000077904D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Shidler, KA: AUTHOR

Abstract

The amplifier provides a negative logical level on output line 20 when light falls on phototransistor T3. The leading edge and trailing edge of the output signal is free from multiple transitions induced by noise, during the time the collector current of phototransistor T3 passes through the threshold level of the amplifier. This is accomplished through employment of capacitive, regenerative feedback by capacitor C1.

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Noise Immune High Gain Photodevice Amplifier

The amplifier provides a negative logical level on output line 20 when light falls on phototransistor T3. The leading edge and trailing edge of the output signal is free from multiple transitions induced by noise, during the time the collector current of phototransistor T3 passes through the threshold level of the amplifier. This is accomplished through employment of capacitive, regenerative feedback by capacitor C1.

Phototransistor T3 is capable of supplying at least 25 microamperes when light impinges thereon. As light falls on phototransistor T3, its collector current begins to build up; and, when the collector current is sufficiently large, transistor T1 begins to conduct, thus supplying base current to transistor T2. As transistor T2 begins to conduct, the collector voltage of transistor T2 goes negative from +5V and this negative voltage transition is coupled back to transistor T1 by capacitor C1, and the amplifier regeneratively switches "on". The time constant associated with capacitor C1 and its driving point resistance is sufficiently long so that transistor T1 is held in a conducting condition, until the collector current of transistor T3 has built up to such a level that the amplifier will be maintained in its conducting condition. This feedback via capacitor C1 eliminates noise sensitivity during the time the collector current is building up in the phototransistor T3.

The operation of the amplifier during...