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Low Cut Leakage T/2/L Circuit

IP.com Disclosure Number: IPCOM000076924D
Original Publication Date: 1972-May-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Culican, EF: AUTHOR

Abstract

Transistor T2 has been added to a usual transistor, transistor logic (T/2/L) circuit in order to limit input leakage current to a few microamps.

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Low Cut Leakage T/2/L Circuit

Transistor T2 has been added to a usual transistor, transistor logic (T/2/L) circuit in order to limit input leakage current to a few microamps.

T/2/L circuits manufactured by a known high-density integrated circuit process, using arsenic subcollectors, have leakage current in the order of a few tenths of a milliamp. The high-leakage currents are caused by the inverted transistor action of transistor T1 when its base-collector junction is forward biased sufficiently to conduct. The inverted transistor action is associated with the emitter that is biased up. T2 effectively clamps the base-to-collector voltage of T2 (VBC) so that it will not conduct and simultaneously supplies the current that the inverted portion of T1 would normally supply.

There are two leakage conditions to be considered. The first is when the input voltage to input 1 is up and the voltage to input 2 is down. Without T2, the current into input 1 is approximately 0.16 milliamp with the current at input 2 at - 1.15 milliamps. Without the leakage problem, the input current at input 1 would be expected to be less than 20 microamps and the current at input 2 would be expected to be in the order of -1.0 milliamp. With T2 in the circuit the leakage is substantially reduced. The base current (IB2) of T2 is 0.003 milliamp so that the minimum drop across the 0.3K resistor is 290 millivolts, which results in less than 10 millivolts difference in biasing. The collector connection of T2 allows this desired result. The base-to-collector voltage (VBC) of T2 is approximately 300 milli...