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Programmable Current Load for Testing Integrated Circuits

IP.com Disclosure Number: IPCOM000043491D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Ayers, RL: AUTHOR [+2]

Abstract

This article describes a circuit which provides constant current load (sync or source) for testing integrated circuits. The circuit can be used with any general-purpose integrated circuit testers to provide the testing function. The programmable current is switched at functional test speeds and requires no software development and minimal hardware cost. The circuit comprises four transistors (Q1-Q4), five diodes (D1- D4, DCL) and two resistors (R1, R2). Q1 and Q2 are a matched pair of PNP transistors which supply negative current Iload. Iload is the source current load which is supplied to the device under test (DUT). The value of the current Iload is determined by the value of Vin and R1 or R2. The polarity of the current Iload is determined by the polarity of Vin.

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Programmable Current Load for Testing Integrated Circuits

This article describes a circuit which provides constant current load (sync or source) for testing integrated circuits. The circuit can be used with any general- purpose integrated circuit testers to provide the testing function. The programmable current is switched at functional test speeds and requires no software development and minimal hardware cost. The circuit comprises four transistors (Q1-Q4), five diodes (D1- D4, DCL) and two resistors (R1, R2). Q1 and Q2 are a matched pair of PNP transistors which supply negative current Iload. Iload is the source current load which is supplied to the device under test (DUT). The value of the current Iload is determined by the value of Vin and R1 or R2. The polarity of the current Iload is determined by the polarity of Vin. The circuit operates as follows: For positive Vin, Q2 and Q4 are off and can be ignored. The positive Vin is applied across the series circuit of R1 and Q3, whose collector and base are shorted. Thus, the current through Q3 is determined from the relation Vin = Vbe3+I3R1, where Vbe3 is the base emitter bias at Q3 and I3 is the emitter current through Q3. Since the bases and emitters of Q1 and Q3 are common, respectively, the base-emitter bias of Q1 is identical to that of its matched twin Q3. Since the gains of Q1 and Q3 also match, the collector current of Q1 is identical to Q3 collector current which for high gains is essentially proportional to the positive values of Vin for a fixed R1. For...