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Three-Level Switch With Override

IP.com Disclosure Number: IPCOM000098061D
Original Publication Date: 1961-Dec-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

McAnney, WH: AUTHOR

Abstract

The three-level switch with override receives a pair of inputs A and B and provides an output that is a function of both of the inputs. Normally, the A or B inputs alone provide an output that is inverse of the input. Whenever the A input is applied, followed by B, the output is controlled by B.

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Three-Level Switch With Override

The three-level switch with override receives a pair of inputs A and B and provides an output that is a function of both of the inputs. Normally, the A or B inputs alone provide an output that is inverse of the input. Whenever the A input is applied, followed by B, the output is controlled by B.

The circuit comprises two identical sections, each including a pair of input transistors coupled to a common base amplifier. The first section includes transistors T1, T2 and T3. The second includes transistors T5, T6 and T4. Transistors T1, T4, and T6 couple to current source 20 of magnitude 21. Similarly, T2 and T3 connect to supply 22 of magnitude 21. The T1 and T6 emitters are clamped to ground by diodes D1 and D4, respectively. The T2 and T5 emitters, however, are clamped to -V2 by diodes D2 and D3, respectively. The T1, T2, T5 and T6 emitters also connect to respective current sinks. The T3 and T4 collectors interconnect and connect to -V by way of load resistor 25. Supply +V1 biases the T3 and T4 bases. Inputs A and B are supplied to T5, T6 and T1, T2, respectively, and are positive, negative and ground. Output 26 connects to the T3 and T4 collectors.

With ground or no input to A and B, T1 and T6 are off. The ground signal is selected to be slightly negative, reversely biasing the emitter base junctions of the respective transistors. T2 and T5, however, are on since their emitters are clamped to a lower potential than the bases. This forwardly biases the transistors into conduction. Current from 22 and 20 divides through T2, T3 and T4, T5, respectively. The current to the load resistor is one unit from supply 20. The output voltage is between that of supply 20 and that for sink 24. When the passive elements are properly selected, this voltage approaches ground.

A positive input to A, with B grounded, produces an output which is the inverse of A. The posi...