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Wide Response Amplifier with Automatic Threshold Control

IP.com Disclosure Number: IPCOM000095179D
Original Publication Date: 1965-Sep-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Braun, RJ: AUTHOR

Abstract

The amplifier has an automatically controlled threshold level. The amplifier is capable of translating a wide range of input values to a nominal range of operating values. Light from a source L impinges on a phototransistor PT. Interruption of the light beam can be utilized to detect passage of documents, punched holes in data cards, etc. PT is connected between a positive source of potential and ground via resistor R1. The input current values in this portion of the circuit can vary over a wide range due partly to variations in light intensity. Such can result from voltage changes on L, aging of L, etc.

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Wide Response Amplifier with Automatic Threshold Control

The amplifier has an automatically controlled threshold level. The amplifier is capable of translating a wide range of input values to a nominal range of operating values. Light from a source L impinges on a phototransistor PT. Interruption of the light beam can be utilized to detect passage of documents, punched holes in data cards, etc. PT is connected between a positive source of potential and ground via resistor R1. The input current values in this portion of the circuit can vary over a wide range due partly to variations in light intensity. Such can result from voltage changes on L, aging of L, etc.

To provide a more reasonable variation in inputs to the amplifier portion of the circuitry, a nonlinear network comprising a plurality of suitably circuited and proportioned zener diodes Z1...Z3 with associated resistors R2...R4 are connected across R1. These combine to form a nonlinear network which provides relatively small change in input voltage to the base of transistor T1 despite large ranges of current through PT.

The emitter of T1 is connected to ground via R5 and R6 and is provided with a time constant network comprising diodes D1 and D2, resistor R7 and capacitor
C. These are proportioned and arranged so that, during a reference period, PT is fully exposed to L for sufficient time to permit C to charge via D1. This charge then establishes a threshold value for subsequent inputs. During the time th...