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Transistor Switch

IP.com Disclosure Number: IPCOM000096423D
Original Publication Date: 1963-May-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Ruoff, CE: AUTHOR

Abstract

The transistor switch operates in a common emitter configuration. It is connected from its base to a diode logic network. For the purpose of noise rejection there is connected a variable-capacitance feedback diode D between collector and base of the transistor. Transient noise appears at the transistor switch whenever changes in the signal voltage level occur at the input terminals due to inherent small capacitance values exhibited by the diodes of the logic network. Thus, it can happen that the transistor switch responds to input signals other than signals representing the logic function. Without any preventive measures, dynamic voltage changes at the inputs can cause the transistor switch to produce some kind of signal at the output sufficient in intensity to be erroneously recognized as a data signal.

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Transistor Switch

The transistor switch operates in a common emitter configuration. It is connected from its base to a diode logic network. For the purpose of noise rejection there is connected a variable-capacitance feedback diode D between collector and base of the transistor. Transient noise appears at the transistor switch whenever changes in the signal voltage level occur at the input terminals due to inherent small capacitance values exhibited by the diodes of the logic network. Thus, it can happen that the transistor switch responds to input signals other than signals representing the logic function. Without any preventive measures, dynamic voltage changes at the inputs can cause the transistor switch to produce some kind of signal at the output sufficient in intensity to be erroneously recognized as a data signal. This circuit eliminates such error signals.

In the non-conducting state of the transistor, the highly reversely biased diode D has a small capacitance C1. This small value still permits an overall high-speed operation of the circuit and a high response to input signals. The feedback from collector to base provided in this state by the value C1 is sufficient for noise rejection. In the conducting state when the transistor is driven into saturation, the slightly forwardly biased diode D exhibits a higher capacitance C2. Thus, D is still maintained in its high resistance region. Capacitance value C2 causes a relatively high negative feedback from c...