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Integrated TMR Sensor with AC Electromagnet and Noise Mitigation

IP.com Disclosure Number: IPCOM000248572D
Publication Date: 2016-Dec-20
Document File: 3 page(s) / 482K

Publishing Venue

The IP.com Prior Art Database

Related People

Tim Jackson: INVENTOR [+2]

Abstract

This information applies to a sensor design and a sensor system based upon tunneled magneto-resistive (TMR) technology; wherein the design of the sensor system results in a highly integrated sensor which eliminates the need for a fixed-field (DC) magnet. The invention further provides a means for detecting/mitigating ambient noise sources which may affect the performance of a present art magnetic sensor.

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Detailed Description

Integrated TMR Sensor with AC Electromagnet and Noise Mitigation

Rev-0,1 18 November 2016 1

This information applies to a sensor design and a sensor system based upon tunneled magneto-resistive (TMR) technology; wherein the design of the sensor system results in a highly integrated sensor which eliminates the need for a fixed-field (DC) magnet. The invention further provides a means for detecting/mitigating ambient noise sources which may affect the performance of a present art magnetic sensor.

Magnet-based Sensors

Prior art magnetic-based sensors typically utilize Hall-effect technology which requires a fixed magnet in order to generate the field detected by the Hall elements. The Hall elements have very little gain so a strong field is necessary in order for the hall effect element to generate signals with sufficient signal-to- noise ratio (SNR.) Recent advances in magneto-resistive technologies have produced silicon sensor for which sensitivity to magnetic fields has increased by orders of magnitude (10x for AMR sensor, 100x for TMR sensors.) compared to the sensitivity of an equivalent Hall-effect sensor. This significant increase in the response of the sensor allows a MR sensor to provide the same performance (as a Hall-effect sensor with a much smaller magnet and/or increased performance with the same sized magnet. Because of the highly sensitive nature of the TMR sensors, the focus of this paper is on that particular MR technology.

Integrated Electromagnet

As with the Hall-effect sensors, the size of a TMR sensor is small enough that it can be co-packaged with the sensor interface IC. There is no novelty in this level of integration. The novelty of the proposed invention is in the implementation of the magnet and the control of said magnet.

As mentioned previously, prior art magnetic sensor utilize a fixed magnet as the moving target for the sensor. The advantage of such magnets is that they can be sized to provide the field strength necessary to achieve the requirements for a given sensor. The disadvantages of fixed magnets are:

• The field strength varies with temperature. Depending on the materials utilized to make the magnet, the temperature variation can be better or worse. Typically magnets with better temperature performance are more expensive.

• The field strength of the magnet decays over time. This decay is effectively a loss of accuracy in the system and this loss must be budgeted into the design of the sensor.

• Any other magnetic fields (AC or DC) which are in close proximity of the sensor appear as noise which degrades the accuracy of the sensor’s measurement.

The present invention seeks to eliminate these disadvantages of prior art magnetic sensors by exploiting the high sensitivity properties of TMR sensors

Present Invention

The present invention represent a unique sensor systems wherein the properties of the TMR sensor allow the fixed magnet to be implemented as an electro-magnet which is driven by...