International Business Machines Corporation

Walter A Svarczkopf

David A Kiesling

Mark D Mayo

Arnold E Barish

A circuit for testing a differential current switching logic circuit of the type including: a bias potential, two resistors connected to the bias potential, and apparatus responsive to an input signal for sinking a first current through a selected one of the resistors so as to generate first and second differential output signals at the resistors. The circuit includes first, second, and third transistors, each having first and second terminals for conducting a current responsive to a signal applied to a control terminal. Apparatus are provided for supplying a current. The first transistor has its first terminal connected to the current supplying means, and its second terminal connected to a circuit node. The second transistor has its first terminal connected to the circuit node, its second terminal connected to the bias potential, and its control terminal connected to sense the potential at a selected one of the resistors. The third transistor has its first terminal connected to the circuit node, its second terminal connected to the selected resistor, and its control terminal connected to sense the potential at the other of the resistors. The circuit functions to sense the potential difference between the first and second differential output signals. When the potential difference is less than a predetermined level, a second current is sunk through the one resistor so as to lower the potential of the output signal associated with the one resistor relative to the potential of the output signal associated with the other resistor.

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Walden, NY, United States of America

Walter A Svarczkopf