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Automatic On Chip Threshold Voltage Compensation

IP.com Disclosure Number: IPCOM000076456D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Forbes, L: AUTHOR

Abstract

This circuit compensates for variations in threshold voltage in field effect transistors (FET).

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Automatic On Chip Threshold Voltage Compensation

This circuit compensates for variations in threshold voltage in field effect transistors (FET).

Transistor T1 is a sensitive sensor of the threshold voltage which exists on the particular semiconductor chip in question. FET T2 serves as a load for T1. The voltage of these FETs is applied to T3 which controls the threshold voltage by controlling the substrate bias. R1 and C1 are a resistor and capacitor mounted on the module or in some other convenient place in the circuit. Both T1 and T3 operate without any substrate-to-source bias. If the threshold voltage of T1 is low when power is applied, it will conduct and lower the gate voltage of T3. This in turn will cause the substrate bias on the chip to increase. If on the other hand, the threshold voltage of T1 is high, then T1 will be normally off and a large gate voltage will be applied to T3 causing the substrate bias applied to the chip to decrease. By controlling the substrate bias applied to the chip, the threshold voltage of an FET in a logic or memory circuit exemplified by T4 is controlled within a relatively narrow range.

Since, at the present time, there is no known way to control process parameters sufficiently to eliminate threshold variations, the present circuit can be used to automatically sample the threshold voltage of a device on a particular chip and automatically adjust the substrate bias to compensate for:
1) varying amounts of oxide charge,
2) va...