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Logic Network Nodal Conductances

IP.com Disclosure Number: IPCOM000083414D
Original Publication Date: 1975-May-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 54K

IBM

Related People

Collins, CA: AUTHOR

Abstract

This circuit measures the conductance of a logic network with respect to ground or power to determine the number of inputs and outputs on a logic network, as well as whether a terminator exists or not. This circuit measures the conductance of a logic network with respect to a reference or power potential, to determine the number of logical elements attached to a network.

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Logic Network Nodal Conductances

This circuit measures the conductance of a logic network with respect to ground or power to determine the number of inputs and outputs on a logic network, as well as whether a terminator exists or not. This circuit measures the conductance of a logic network with respect to a reference or power potential, to determine the number of logical elements attached to a network.

The circuit uses an operational amplifier 10 to measure conductance by measuring the current I1, which is resultant from a constant voltage E1 - E2 applied across the network. The location of the amplifier 10 in the circuit is the key to prevent extraneous current paths, which would detract from the quality of the measurement. As can be seen from the figure, the potential of the 2 logic circuit bias terminals is maintained at the same value, thus preventing a current to flow between these 2 terminals. The sum of the currents into the (-) input terminal of the amplifier results in an output voltage E0 as follows. E0 = E2 - (I1-I2)R1 (eq 1).

Assuming for the moment that the connection to R2 does not exist the following are the basic equations of the operation of the circuit:

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This concept can be used in inline testing and as a diagnostic tool, to investigate the characteristics and quality of the input and output circuits attached to a logic network. Furthermore, it can be used on a troubleshooting tool during system debug to determine if a particular...