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TTL FET Logic Probe Front End Circuitry

IP.com Disclosure Number: IPCOM000083248D
Original Publication Date: 1975-Apr-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Rayburn, SD: AUTHOR [+2]

Abstract

This circuit is particularly useful in detecting whether the voltage level at a particular point in an electronic circuit under test is within certain predetermined ranges. The output voltages are shown below for various input conditions. VIN VOUT VOUT 0 0 -60V to 0.95V 4.2V 3.0V 0.95V to 2.16V 4.2V 4.2V 2.16V to +60V 3.0V 4.2V INPUT FLOATS 4.2V 4.2V.

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TTL FET Logic Probe Front End Circuitry

This circuit is particularly useful in detecting whether the voltage level at a particular point in an electronic circuit under test is within certain predetermined ranges. The output voltages are shown below for various input conditions.

VIN VOUT VOUT 0 0 -60V to 0.95V 4.2V 3.0V
0.95V to 2.16V 4.2V 4.2V
2.16V to +60V 3.0V 4.2V

INPUT FLOATS 4.2V 4.2V.

With the above values of 0 and 0, it is possible to control a suitable display lamp, not shown, to indicate the input condition being detected. In addition, the circuit will provide outputs which will switch state, when a single 6 nanosecond (ns) wide pulse (measured at 1.4V with 1 ns rise and fall time) is applied at the input. The output will switch back within 15 ns after the pulse leaves.

In essence, the circuit is divided into functional halves. The upper half responds to fast negative-going pulses. The lower half responds to fast positive- going pulses.

On the front of each half there is an emitter-follower made from two transistors in a Darlington connection. The PNP emitter-follower drives the upper half and the NPN one drives the lower half.

The upper and lower comparators, including transistors T9, T10 and T7, T8, respectively, determine the boundary voltage levels for the "gray" zone (0.95V to
2.16V).

Transistors T11, T12, and T13 provide power gain and proper phasing of the signals.

Transistors T5 and T6 aid the turncff of the Darlington emitter-followers.

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