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APPLICATION INFORMATION

GIANT MAGNETORESISTANCE VERSUS HALL EFFECT—ACOMPARISON OF TECHNOLOGIES FOR SPEED SENSORAPPLICATIONS
By Braeden Benedix, Chris Dean, Zachary Richards
Allegro MicroSystems

INTRODUCTION
Automotive and industrial systems rely on speed sensor
technology to sense the rotational movement of a magnetic
encoder or a ferrous gear. Hall-effect technology offers atime-tested and trusted speed sensing solution. However,
newly emergent cutting-edge devices that leverage themagnetoresistance (MR) effect may be able to deliver significant performance improvements. Allegro MicroSystems
giant magnetoresistance (GMR) effect technology [1] offerings build on lessons learned from experience with Halleffect devices to enable new options for speed sensing
system design. To help users determine if the new GMR
technology is appropriate for a specific application, thisapplication note compares Hall-effect and GMR technologies and provides straightforward reference tables to help
users choose the best device. Proper use of a GMR device
may allow for revolutionary breakthroughs in system-level
capabilities.

Figure 1: Simplified Hall plate diagram.

Hall-effect device characteristics significant to speed sensing applications include:• Unidirectional magnetic field sensitivity: A planar
Hall-effect device is only sensitive to magnetic fields inone direction—into the branded face of the packaged
integrated circuit (IC), perpendicular to the silicon.

OVERVIEW OF BASIC PRINCIPLES• Linear transducer output: Over a large signal range, thetransducer output remains linear.

Hall-Effect Technologies• High field strength robustness: The ability to withstandstrong magnetic fields enables operation with a verysmall minimum air gap and a moderate maximum air gap.

Hall-effect sensing elements generate a voltage that is
proportional to the magnitude of a nearby magnetic field.
Hall sensor technology is an application of Lorentz force,
which is the force exerted on electrons as the electrons
move across a plate perpendicular to a magnetic field. The
electron movement ultimately induces a voltage difference
across the plate, as shown in Figure 1. Amplification of thisinduced voltage change is the basis of the Allegro Halleffect speed sensor technology.
[1] https://www.allegromicro.com/en/insights-and-innovations/allegro-technology/gmr-technology

To facilitate most design requirements, Allegro Hall-effectdevices are typically available either:• With a back-biasing magnet included inside the package,
which simplifies system design; or• Without an integrated magnet, which facilitates use of
specific magnetic encoder or custom magnet designs.

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APPLICATION INFORMATIONGMR Technologies
GMR sensing elements respond to magnetic vectors, andGMR sensor technology operates on the principles of spintransport electronics. In a magnetoresistor, electron scattering rates increase or decrease as a function of the interactionof the spin state of the electrons and the magnetic orientation of the medium in which the electrons travel. Electron
scatter increases the mean free path of the electron flow,which effectively alters the resistance of the medium. Thus,in the presence of a magnetic field, the resistance value ofa magnetoresistor changes as a function of the cosine of
the applied external magnetic field relative to the reference
layer in the plane parallel to the silicon surface, as shown in
Figure 2.

ϴBiCMOS

Figure 3: GMR sensor IC monolithic solution—Simplified layer cross section.

HOW TO CHOOSE A TECHNOLOGYTo enable designers to select the best technology for anapplication, performance metrics of interest for transducers
that use the Hall effect and the GMR effect are discussed
here and are compared in Table 1.
Table 1: Transducer Type Performance Metric Comparison
PerformanceMetric(Orientation B)

BAPP

Hall

Sensitivity

Low to medium

High, roughly 50 times
greater than HallLinearity

Large linear range

Limited linear range

Sensing Range(Response Area)

Virtually infinite
magnetic range

Limited and related tosensitivity [1]Sensing Plane

Perpendicular toIC: Planar Hall
Parallel to IC:
Vertical Hall

Parallel to IC [2]

Air Gap

Closest minimum
air gap, andmoderatemaximum air gap

Potentially limited
minimum air gap, butlarge maximum airgap (greater than 50%
improvement comparedto Hall, in most cases)

Jitter/Repeatability

Standard

Best edge repeatability

Sensing Principle

Lorentz force

Spin-transport
electronics(Orientation A)
Rmin

Spin
Valve

Rmax

Rmean

Rmean

Free Layer(BAPP)
Spacer
Reference
Layer
Wafer

Output Voltage (V)R ∝ cos(ϴ)–100

GMR Response7.5%
MR[1] Allegro designs are capable of operation in the saturation

100 300 500 700
0 200 400 600 800
Angle (Degrees)

Figure 2. Simplified GMR structure and response to applied magnetic fieldorientation.

Allegro GMR transducers are built in a complex stack ofadditional layers (of various proprietary formulations) overan independent BiCMOS process as shown in Figure 3. The
process achieves a monolithic single-die solution. Compared to multi-die predecessors that employ one die for theBiCMOS core IC and another for the MR sensing elements,
the single-die approach is a simpler, more robust solution
with a smaller form factor.

GMRregions, design dependent.

[2] Allegro back-biased designs are compatible with Hallmountings. Allegro SIP packages can sense in parallel andperpendicular orientations.

Sensitivity
Compared to a Hall-effect device, GMR technology offers
much greater transducer sensitivity, which results in:• Better maximum air gap, which eases mechanicaltolerances and provides design margin and flexibility; and• Lower jitter (greater repeatability) performance, whichincreases the accuracy of the speed data so as to provide
the system with better clarity and less noise.

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2

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APPLICATION INFORMATIONAir Gap
The increased sensitivity of a GMR device imposes certain
minimum air gap restrictions and linearity considerations.
For example, the Allegro ATS19580 back-biased GMR
transmission speed sensor IC—the successor to the Allegro
ATS19520 Hall-effect sensor IC—requires a minimum air gapof 1.5 mm. This represents a 1 mm increase in the minimum
air gap (the Hall-effect device has a minimum air gap of0.5 mm). However, the 4.5 mm maximum air gap of theGMR device is 1.7 mm greater than the 2.8 mm maximum airgap of the Hall-effect device. Thus, the GMR solution represents a maximum air gap improvement of greater than 60%
and a total air gap range improvement of greater than 30%.

For GMR-suitable applications, the selection of popular
Allegro GMR sensors in Table 3 summarizes strengths of individual products to help designers determine the best device
for specific application needs.
Table 3: Released Allegro GMR Speed Sensor ICs
Part Number [1]Sensor Field Orientation

Low
Priority

Low
Priority

Hall2

Low
Priority

HighPriority

Low
Priority

GMR

3

Low
Priority

Low
Priority

HighPriority

GMR

High-Accuracy Full-Pitch
Vibration-Tolerant Speedand Direction

A19570 [5]Magnetic Encoder

Large Air Gap, FullPitch Vibration-Tolerant,
Small-Pitch Speed andDirection

A19571 [6](GMR alternativeto predecessor
A19520 [7] Halleffect device)

Magnetic Encoder

Large Air Gap, FullPitch Vibration-Tolerant,
Large-Pitch Speed andDirection

Ferrous Gear

Large Air Gap, FullPitch Vibration-Tolerant,Speed and Direction
Sensor IC with
Integrated Magnetcompatible (EMC) protection components in a single
overmolded package.
[2] All products offer ISO 26262 ASIL integrated diagnostics andcertified design process with optional reporting protocol.
[3] https://www.allegromicro.com/en/products/sense/magneticspeed/wheel-speed-sensor-ics/a19250[4] https://www.allegromicro.com/en/products/sense/magneticspeed/wheel-speed-sensor-ics/a19350[5] https://www.allegromicro.com/en/products/sense/magneticspeed/transmission-sensor-ics/a19570[6] https://www.allegromicro.com/en/products/sense/magneticspeed/transmission-sensor-ics/a19571[7] https://www.allegromicro.com/en/products/sense/magneticspeed/transmission-sensor-ics/a19520[8] https://www.allegromicro.com/en/products/sense/magneticspeed/transmission-sensor-ics/ats19580[9] https://www.allegromicro.com/en/products/sense/magneticspeed/transmission-sensor-ics/ats19520

Table 2: Simplified Technology Selection Guide

HighPriority

Magnetic Encoder[1] All products are offered with integrated electromagnetic-As discussed throughout this document, each technology has its relative strengths. The simplified priority-driven
technology selection guide in Table 2 summarizes thesestrengths to help designers determine the most appropriatetechnology for an application.

1High-Accuracy Speed

ATS19580 [8](GMR alternativeto predecessor
ATS19520 [9] Halleffect device)

SIMPLIFIED SELECTION TABLES

Low Jitter

Magnetic Encoder

A19350 [4]Transmission Sensor IC, Back-Biased

As previously discussed, sensor field orientation is anotherimportant consideration: GMR elements sense fields in theplane of the silicon (parallel to the IC), whereas typical Halleffect devices sense fields perpendicular to the IC. To reduce
design considerations related to this orientation change andto facilitate transition from predecessor Hall-effect technology to GMR technology, the new ATS19580 GMR device isdesigned to be a drop-in replacement for the predecessor
ATS19520 Hall-effect device.

LargeMaximum
Air Gap

A19250 [3]Transmission Sensor IC

GMR-effect sensor ICs improve repeatability compared toHall-effect counterparts. For example, at the maximum airgap, the Allegro A19571 GMR transmission speed sensor
IC provides a full order-of-magnitude improvement in jittercompared to its Allegro Hall-effect predecessor A19520.

SmallMinimum
Air Gap

Description [2]Wheel Speed Sensor ICs

Repeatability

Scenario

Target TypeSelection
AdviceCONCLUSION
The Allegro MicroSystems comprehensive magnetic speed
sensor portfolio includes both GMR and Hall technologies.
With many output protocol options, the Allegro portfolio
offers a solution for any application need. The guidance inthis application note should be used to help select the mostsuitable device type for a specific speed sensing application.

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Revision History
NumberDate

Description

Responsibility–December 17, 2021

Initial release

Z. E. Richards

Copyright 2021, Allegro MicroSystems.

The information contained in this document does not constitute any representation, warranty, assurance, guaranty, or inducement by Allegro to the customer with respect to the subject matter of this document. The information being provided does
not guarantee that a process based on this information will be reliable, or that Allegro has explored all of the possible failuremodes. It is the customer’s responsibility to do sufficient qualification testing of the final product to ensure that it is reliable andmeets all design requirements.
Copies of this document are considered uncontrolled documents.

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