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Beta Booster

IP.com Disclosure Number: IPCOM000089453D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Gersbach, JE: AUTHOR

Abstract

This article teaches that the current gain of bipolar transistors can be increased by biasing the collector emitter circuit near its open base breakdown voltage. The usual equation for Beta is Beta = Alpha/1-Alpha. A more complete equation includes the collector multiplication factor M. Beta = M Alph/1-M Alpha where M = 1/1-(Vcb/BVcbo) . M will increase to infinity as the collector-to-base voltage approaches its breakdown voltage, and Beta will approach infinity as M Alpha approaches unity or as M approaches 1/Alpha. M' will approach unity as the collector base voltage approaches the open base breakdown voltage BVceo. Therefore, if the collector voltage is biased slightly below the BVceo, B will be significantly and predictably higher. The above circuit shows one implementation of this mechanism.

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Beta Booster

This article teaches that the current gain of bipolar transistors can be increased by biasing the collector emitter circuit near its open base breakdown voltage. The usual equation for Beta is Beta = Alpha/1-Alpha. A more complete equation includes the collector multiplication factor M. Beta = M Alph/1-M Alpha where M = 1/1-(Vcb/BVcbo) . M will increase to infinity as the collector-to-base voltage approaches its breakdown voltage, and Beta will approach infinity as M Alpha approaches unity or as M approaches 1/Alpha. M' will approach unity as the collector base voltage approaches the open base breakdown voltage BVceo. Therefore, if the collector voltage is biased slightly below the BVceo, B will be significantly and predictably higher. The above circuit shows one implementation of this mechanism.

The input impedance of the amplifier T1 and T2 is raised as a result of the increased current gain Beta. T3, T4, T5 and T6 cause the voltage across T1 and T2 to be nearly BVceo. T4 is allowed to breakdown by virtue of its floating base. T3 will not breakdown because of its low base impedance and the drop across R in its emitter circuit. The voltage across T1 and T2 will be the same as that of T4-V(R). The output current is taken from the collectors of T5 and T6. The power supply must be greater than BVceo, and the transistors must be on the same chip to ensure tracking of the breakdown voltages.

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