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Feedback Switching Circuit

IP.com Disclosure Number: IPCOM000090613D
Original Publication Date: 1969-Jun-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Weiss, L: AUTHOR

Abstract

This switching circuit provides steady-state negative feedback from an in-phase output to compensate for the emitter-base voltage drop associated with an emitter-follower. Positive feedback is employed in the circuit to improve noise tolerance during input switching transitions.

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Feedback Switching Circuit

This switching circuit provides steady-state negative feedback from an in- phase output to compensate for the emitter-base voltage drop associated with an emitter-follower. Positive feedback is employed in the circuit to improve noise tolerance during input switching transitions.

Emitter-followers 1 are coupled to current switch 2-3 which provides true and complement outputs to emitter-followers 5 and 4 respectively. Emitter-followers 1 provide high input impedance. Switch 2-3 is isolated from input-output considerations. The isolated current switch is optimized for a minimum RC time constant at the collector node as well as the deletion of the collector capacitance due to fan-in.

A negative feedback from the true output or emitter-follower 5 to the reference voltage of switch 2-3 compensates for the emitter-base voltage drop of emitter-follower 1. The feedback node tracks the input to switch 2-3 by virtue of emitter-base voltage of emitter-follower 5 tracking the emitter-base voltage of emitter-follower 1. Changes in the emitter-base voltage due to temperature provide a similar feedback efficiency.

Positive feedback is provided from resistor RF through capacitor C to the base of switch transistor 3. The positive feedback changes the reference base potential relative to the input potential to switch transistor 2. This allows the circuit to have noise tolerance to reflections and skin effects that normally occur at the latter part of the...