Browse Prior Art Database

Variable Threshold Circuit

IP.com Disclosure Number: IPCOM000080645D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Cassidy, BM: AUTHOR [+2]

Abstract

The circuit described herein varies the voltage applied to the channel region of a field-effect transistor (FET) to vary the threshold of the FET, by setting the FET in the feedback loop such that as the current through the FET falls, the voltage applied to the channel region of the FET rises which, in turn, causes the threshold voltage of the FET to fall.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 82% of the total text.

Page 1 of 2

Variable Threshold Circuit

The circuit described herein varies the voltage applied to the channel region of a field-effect transistor (FET) to vary the threshold of the FET, by setting the FET in the feedback loop such that as the current through the FET falls, the voltage applied to the channel region of the FET rises which, in turn, causes the threshold voltage of the FET to fall.

The input to the gate of transistor T1 is VR, which is the voltage that determines the threshold of the device. The approximate equalizing of the gate voltage VR of transistor T1 and the threshold voltage of the device occurs, because the drain voltage of transistor T1 is determined by the current going through transistor T2 and this current is adjusted as follows.

The substrate of transistors T4, T5, and T7 are all connected to a voltage source V3, which guarantees that they all operate in the enhancement mode when their sources are connected to -5 volts. In this condition, transistor T5 operates in the saturation mode and transistors T3 and T6 are also operating in the saturation mode. Thus, the gate-to source voltage of transistor T3 equals the gate-to-source voltage of transistor T6. This causes the voltage on the gate of T7 to go down as the voltage on the gate of T3 rises and vice versa. This means that if the threshold of transistor T1 rises, the current through transistor T1 falls which, in turn, causes the voltage on the gate of T3 to rise, causing the voltage on the gate of...