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Hall Effect Device Feedback Circuit

IP.com Disclosure Number: IPCOM000073757D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Collins, TW: AUTHOR

Abstract

A MOS FET Hall effect device is used consisting of a regular insulated gate field effect transistor with the addition of Hall contacts 1 and 2 connected to the conducting channel, as shown in drawing A. When a potential is applied to the gate, an inversion layer is formed and current is conducted from the drain to the source. In the presence of a transverse magnetic field B normal to the surface of the gate, the Lorentz force diverts the carriers to one side of the gate or the other. Under equilibrium conditions, a retarding field due to these diverted carriers is built up and no further deflection of carriers is experienced. This restraining field is sensed as the Hall field or Hall voltage. The Hall voltage as a function of gate voltage is shown in the approximate curve of drawing B.

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Hall Effect Device Feedback Circuit

A MOS FET Hall effect device is used consisting of a regular insulated gate field effect transistor with the addition of Hall contacts 1 and 2 connected to the conducting channel, as shown in drawing A. When a potential is applied to the gate, an inversion layer is formed and current is conducted from the drain to the source. In the presence of a transverse magnetic field B normal to the surface of the gate, the Lorentz force diverts the carriers to one side of the gate or the other. Under equilibrium conditions, a retarding field due to these diverted carriers is built up and no further deflection of carriers is experienced. This restraining field is sensed as the Hall field or Hall voltage. The Hall voltage as a function of gate voltage is shown in the approximate curve of drawing B.

The feedback circuit is shown in drawing C. When the magnetic field is applied, a Hall voltage VH is obtained and fed into a differential amplifier 3. The output of amplifier 3 is fed back to the gate of the FET 4 as either positive or negative feedback. This feedback voltage will change the gate voltage which in turn changes the Hall voltage. This process continues until the error voltage is zero in the case of negative feedback or until a nonlinearity stops the process in the case of positive feedback. This circuit employs the amplifying capability of the FET Hall effect device to amplify the detected signal caused by the application of a magne...