Browse Prior Art Database

Converter Circuit

IP.com Disclosure Number: IPCOM000082284D
Original Publication Date: 1974-Nov-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Parker, CP: AUTHOR

Abstract

The circuit shown provides a means for interconnecting ground-down logic circuitry and ground-up logic circuitry.

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Converter Circuit

The circuit shown provides a means for interconnecting ground-down logic circuitry and ground-up logic circuitry.

The circuit comprises a grounded-base output transistor T4 capable of handling 8 milliamperes. The emitter of T4 is connected to a current source comprising R1, T2 and T3. The output transistor T4 has a current gain very nearly unity and its emitter, when off, floats up towards ground minimizing the collector-emitter voltage. When the input is DOWN, T1 is off, and a current of essentially 1.5-Vbe over R1 flows into the collector of T2.

By reason of the transistor matching, inherent in large-scale integration (LSI), a similar current density is required in T3 for equilibrium. Thus, a current approximately equal to 4 x 1.5-Vbe is pulled from the emitter of T4 and hence from the output node. When the input is UP, the base of T3 is pulled down to Vce (clamped) and T3 is switched off. As previously described, the emitter of T4 floats up switching T4 off, and minimizes the Vce across T4.

The circuit requires a pull-up network connected to the output to establish the upper level. A suitable network would be 2k ohms to +3 volts (or the Thevenin equivalent). With this loading on the output and a value of 500 ohms for R1, the circuit can drive two logic circuits.

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