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Field Effect Transistor as a Linear Variable Resistance

IP.com Disclosure Number: IPCOM000095783D
Original Publication Date: 1964-Jun-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Elliott, WY: AUTHOR

Abstract

The field effect transistor can be advantageously utilized as a voltage-controlled variable resistance where the control voltage may be of either polarity. This is accomplished without requiring the passage of a DC bias current through the resistance. However, when used in this way with usual biasing methods, a high degree of non-linearity of result is obtained. The essential effect gained by the technique described here is a vastly improved linearity.

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Field Effect Transistor as a Linear Variable Resistance

The field effect transistor can be advantageously utilized as a voltage- controlled variable resistance where the control voltage may be of either polarity. This is accomplished without requiring the passage of a DC bias current through the resistance. However, when used in this way with usual biasing methods, a high degree of non-linearity of result is obtained. The essential effect gained by the technique described here is a vastly improved linearity.

When the source and drain are maintained at substantially equal and oppositely poled potentials (V1 - drain potential, V2 - source potential), as in the first drawing, considerable improvement in linearity is obtained. Exemplary of the improved characteristic are the graphical results shown for this case where V3 = V1 - V2 and the current 14 is the source-to-drain current.

In certain situations it may not be possible or feasible to maintain the drain and source potentials at the above prescribed values V1 = - V2. However, enhanced linearity can be achieved by superimposing approximately one-half the signal potential available at the drain onto the gate bias with the source held at ground potential. The lower drawing shows an arrangement for accomplishing this.

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