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T/2/L and Current Switch Emitter Follower Logic Blocks

IP.com Disclosure Number: IPCOM000076431D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Mathews, KF: AUTHOR [+2]

Abstract

This circuit provides an interface between low-level transistor transistor logic (T/2/L) and current switch emitter-follower logic (CSEF) in a unified power supply system. The circuit accepts low-level T/2/L logic levels and drive currents, and converts them to CSEF voltage levels. The output is capable of driving as many as ten separate loads.

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T/2/L and Current Switch Emitter Follower Logic Blocks

This circuit provides an interface between low-level transistor transistor logic (T/2/L) and current switch emitter-follower logic (CSEF) in a unified power supply system. The circuit accepts low-level T/2/L logic levels and drive currents, and converts them to CSEF voltage levels. The output is capable of driving as many as ten separate loads.

Transistors T1, T2, and T3 and resistors R1, R2, R3, and R4 constitute a circuit configuration similar to a low-level T/2/L circuit. However, the series combination of R3 and R4 replaces the conventional pull-up output resistor normally found in a T/2/L circuit, and also functions to simulate a current switch collector resistor for driving the emitter-follower circuit constituted by T5. Transistor T4 clamps the down level input into the base of transistor T5 and prevents transistor T2 from heavily saturating, and also controls the down level of the output terminal. With the emitter terminals of T1 more positive than -0.10 volt, transistor T1 operates in a reverse manner and drives current from its collector into the base of T2. The emitter current of T2 develops a voltage across R2 which biases T3 into conduction. As T2 begins to conduct more heavily, transistor T3 is driven harder into conduction thus taking more current from T2. This feedback action coupled with the clamping action of transistor T4 prevents T2 from heavily saturating.

With the emitter of transistor T...