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MOS Transistor Electronic Stabilization of Thresholds

IP.com Disclosure Number: IPCOM000093343D
Original Publication Date: 1967-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Pleshko, P: AUTHOR [+2]

Abstract

This circuit arrangement reduces threshold variations in FET devices from chip to chip. The variation of the threshold voltage of FET devices from chip to chip can be due to differences in production runs and to threshold drift due to aging. Arrangements to accommodate wider threshold variations require higher voltage levels which in turn lead to increased either dissipation or slower performance or both. The threshold voltage of an FET device is a function of the voltage applied to the substrate. The problem of variations in threshold voltage from chip to chip and with aging can be overcome by regulating the substrate bias applied to a chip by a circuit on the chip. Thus, each chip is individually biased with the proper substrate voltage to obtain a given threshold. An example of a circuit to accomplish this is shown.

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MOS Transistor Electronic Stabilization of Thresholds

This circuit arrangement reduces threshold variations in FET devices from chip to chip. The variation of the threshold voltage of FET devices from chip to chip can be due to differences in production runs and to threshold drift due to aging. Arrangements to accommodate wider threshold variations require higher voltage levels which in turn lead to increased either dissipation or slower performance or both. The threshold voltage of an FET device is a function of the voltage applied to the substrate. The problem of variations in threshold voltage from chip to chip and with aging can be overcome by regulating the substrate bias applied to a chip by a circuit on the chip. Thus, each chip is individually biased with the proper substrate voltage to obtain a given threshold. An example of a circuit to accomplish this is shown. N-channel devices are assumed.

In operation, a voltage is applied to the substrate S of Q1.

This voltage differs from -V2 by the drop across resistor R3, which in turn is determined by the current flowing in Q2. The current through Q2 is a function of the voltage on the gate of Q2, point C.

This in turn depends upon the voltage drop across resistor R1, which depends upon the current in Q1. This last mentioned current depends upon the difference between the reference voltage Vref on the gate of Q1 and the threshold of device Q1.

The proper substrate voltage is applied to Q1 to result in a drop ac...