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A Mosfet Overvoltage/undervoltage Detection Circuit

IP.com Disclosure Number: IPCOM000062011D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Cranford, HC: AUTHOR [+2]

Abstract

Described is an overvoltage/undervoltage detection circuitry whose detection level can be changed by altering the width-to- length (W/L) ratio of certain devices in the circuit.

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A Mosfet Overvoltage/undervoltage Detection Circuit

Described is an overvoltage/undervoltage detection circuitry whose detection level can be changed by altering the width-to- length (W/L) ratio of certain devices in the circuit.

With reference to the figure, devices T1 and T2 are biased in the linear region to form a voltage divider circuit. As Vdd increases, node A rises above the sum of Vt4 and Vt5 to switch T4 on. Node C then rises to a voltage determined in part by the ratio of the W/L's of devices T3 and T5, respectively. As node B falls below an enhancement threshold, device T6 switches off and the output (node D) rises. This indicates that Vdd is above the level determined by the divider formed by devices T1 and T2, respectively. Thus, the actual switching point of this circuit is determined by the level set by devices T1 and T2 and its relationship with V5. The effects of threshold voltage variation may largely be compensated for by the proper selection of device sizes.

For a given power supply (Vdd) level the voltage at node A will be set by the depletion thresholds of devices T1 and T2, respectively. Since the thresholds of devices T1, T2 and T5 track, V5 will be higher when V2 is higher and lower when V2 is lower. The tracking of V2 and V5 compensates for the threshold voltage variation and maintains a nearly constant switch point.

Disclosed anonymously.

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