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Impedance Comparator using Exponential Current Source

IP.com Disclosure Number: IPCOM000092732D
Original Publication Date: 1967-Jan-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Ristad, CH: AUTHOR

Abstract

Unknown impedance 1 is compared with reference impedance 1' to determine whether the difference in value exceeds a given percentage tolerance. The feature of the test is that all impedance levels, within the range of the tester, are tested to the same percentage tolerance without the need for programming such tolerance. Impedances other than resistors can be tested.

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Impedance Comparator using Exponential Current Source

Unknown impedance 1 is compared with reference impedance 1' to determine whether the difference in value exceeds a given percentage tolerance. The feature of the test is that all impedance levels, within the range of the tester, are tested to the same percentage tolerance without the need for programming such tolerance. Impedances other than resistors can be tested.

To make this test, impedance 1' and impedance 1 are connected in series to a current source. The latter starts at a small quiescent value and increases with time. When the voltage across either impedance reaches a fixed reference, counter 3 is started. It is the higher impedance that starts counter 3. Later the voltage across the lower impedance reaches the same reference and counter 3 is stopped. If the count is lower than a preset amount, a go signal is generated. If the count is higher than this amount, a no-go is generated. To insure that all impedance levels are tested to the same percentage tolerance while the count corresponding to a go, no-go threshold is fixed at a preset value, the applied current source is required to increase exponentially with time.

The plural pin circuit module 4 is to be tested. Identical module 4' meets specifications accurately. The impedance between each pin and all other pins on module 4 is to be tested. A program-controlled switch assembly 5 sequentially connects each pin such as 7 and each remaining pin such as...