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Binary Switching Circuit

IP.com Disclosure Number: IPCOM000074826D
Original Publication Date: 1971-Jun-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Walsh, JL: AUTHOR

Abstract

This circuit operates with a small input signal swing, minimum power dissipation, and high noise rejection when measured as a per cent of the total input signal. An input signal 10 is applied to base input terminal 12 of NPN input switching transistor T1. Voltage source +V is connected directly to the collector of NPN transistor T2 and to node 14 via biasing resistor 16. Output node 18 is connected to the emitter of transistor T2 and to the base of NPN transistor T3, which in turn is connected at its collector terminal to the emitter of transistor T1. Resistors 19 and 20 are connected to the emitter of transistor T3 and to output node 18, respectively, and then to ground potential. The binary output signal produced by the switching circuit is illustrated at 22.

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Binary Switching Circuit

This circuit operates with a small input signal swing, minimum power dissipation, and high noise rejection when measured as a per cent of the total input signal. An input signal 10 is applied to base input terminal 12 of NPN input switching transistor T1. Voltage source +V is connected directly to the collector of NPN transistor T2 and to node 14 via biasing resistor 16. Output node 18 is connected to the emitter of transistor T2 and to the base of NPN transistor T3, which in turn is connected at its collector terminal to the emitter of transistor T1. Resistors 19 and 20 are connected to the emitter of transistor T3 and to output node 18, respectively, and then to ground potential. The binary output signal produced by the switching circuit is illustrated at 22.

The load on the collector diode of transistor T3 is the emitter-base diode of transistor T1. Accordingly, it can be seen that the input signals, e.g., 10 are applied in a push-pull manner across the emitter-base diode of transistor T1, and as such provides positive feedback by way of transistor T2. However, once the input transistor T1 is switched the feedback becomes negative and prevents transistor T1 from saturating. Thus, transistor T1 presents a virtually zero current load to transistor T3. When the output signal goes negative, transistor T3 switches out of saturation to the active region and the base current necessary to discharge capacitive loads, not shown, is significantly...