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Input Buffer Circuit

IP.com Disclosure Number: IPCOM000094759D
Original Publication Date: 1965-May-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Clapper, GL: AUTHOR

Abstract

This circuit has low power dissipation, noise-free output with controlled rise and fall times, a level-setting action for variable inputs, and no feed through in either direction. The circuit has low impedance and high current handling capabilities. The circuit comprises an inverting amplifier including transistor T1 which feeds a clamped integrator output circuit including transistor T2. A regenerative feedback connection from the output is provided via resistor R1 to the base of T1.

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Input Buffer Circuit

This circuit has low power dissipation, noise-free output with controlled rise and fall times, a level-setting action for variable inputs, and no feed through in either direction. The circuit has low impedance and high current handling capabilities. The circuit comprises an inverting amplifier including transistor T1 which feeds a clamped integrator output circuit including transistor T2. A regenerative feedback connection from the output is provided via resistor R1 to the base of T1.

This produces a desirable hysteresis action so that the output can be on or off for wide ranges of input signals. These can overlap by any desired amount depending upon the value of R1. An AC feedback between the output and the base of T2 is provided via capacitor C1. Clamp diode D1 clamps the output near ground while diode D2 holds the base of T2 to a value such that T2 is never far from an active conductive condition.

When the output is off, at about -6 volts, the input can range in value, for example, from -10 volts or lower to -2.5 volts, with no effect on the output level. T1 conducts throughout this range from current supplied by the input plus the current supplied through R1. With T1 conducting, T2 is held in a state of conduction by current flowing in resistor R2 from the collector of T1 to the base of T2.

Any attempt by outside loading to raise the voltage of collector T2 feeds back to the base of T2 by C1. This feedback serves to clamp the collector ev...