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A Voltage Discriminator

IP.com Disclosure Number: IPCOM000093546D
Original Publication Date: 1967-Oct-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Cole, TG: AUTHOR

Abstract

The circuit is a voltage discriminator whose input threshold is depend-end only upon two power supply voltages. The circuit is a cascaded connection of two single transistor circuits. A voltage-to-current converting stage T1 and R1 feeds a current threshold stage T2, D1 and R3. A current source is produced by E2 and R2.

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A Voltage Discriminator

The circuit is a voltage discriminator whose input threshold is depend-end only upon two power supply voltages. The circuit is a cascaded connection of two single transistor circuits. A voltage-to-current converting stage T1 and R1 feeds a current threshold stage T2, D1 and R3. A current source is produced by E2 and R2.

In the circuit E3 and R3 are sufficiently large to define a constant current through R3 and E1 is greater than E2. Initially the input is held sufficiently positive so that T1, T2, and D1 conduct.

When the input voltage V is reduced, the current IT1 is reduced, the collector of T1 goes positive, the current IT2 increases thus reducing the current ID1. At the threshold voltage, when V is fractionally larger than E1-E2, T2 saturates end D1 is cut off and the constant current IR3 flows through T2. The collector voltage of T2, which is previously the sum of the voltages across the diode and from base to emitter of T2, falls to the saturation voltage of T2. Fast switching is obtained as both transistors are in the active region at the threshold.

By making R1 = R2 and having matched transistor base-emitter characteristics, the input voltage threshold is made only dependent upon the difference between voltages E1 and E2.

The diode current ID1 is given by (E1-E2-V)/R1. Thus the current ID1 is equal to zero when at the threshold V = E1-E2.

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