Magnetic-Hall effect Based Sensors

Sanjay JagarwalB.Tech Chemical 3rd year

Hall effect

The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current.

Discovered by Edwin Hall in 1879.

Hall effect

Lorentz Force: F = q[E + (v x B)]

•Hall voltage is produced by charge accumulation on sidewalls.•Charge accumulation balances Lorentz Force.•Charge accumulation increases resistance.

Typical Shapes of Hall Sensors:

Hall plate area should be small. To accuratly measure magneticflux density, Hall plate area should be smaller than cross section of field being measured.Transverse (useful when fields must be measured in thin gaps.)Can be as small as .006”

Axial (useful when field is parraellel to axis of hole. Traveiling wave tubes or solenoids.)Can be as small as .063” in diameter.

Hall voltage

VH IBned

RHIB

d

For simple conductors;

Where n = carrier density, d = conductor length• RH is known as the Hall coefficient

• VH α B Useful for measuring B-Fields

Gaussmeter Probe uses a hall sensor

• The Hall coefficient is the ratio of the induced electric field to the product of the current density and the applied magnetic field.

• It is a characteristic of the material from which the conductor is made.

• The value of Hall coefficient depends on the type, number, and properties of the charge carriers that constitute the current.

Hall coefficient 𝑅𝐻=𝐸 𝑦

𝑗𝑥 𝐵

Hall effect in semiconductorsWhy Semiconductors?

• Ideal number of charge carriers• Charge carriers increase with temperature

For moderate magnetic fields the Hall coefficient is;

For large applied fields; where

Enables us to determine the carrier density.

Hall effect type• Magnetic Hall effect

• Quantum Hall effect

• Spin Hall effect

• Quantum spin Hall effect

• Anomalous Hall effect

Magnetic Hall effect sensors

• A Hall Effect sensor is a transducer which varies its output voltage in reaction to a magnetic field.

• These type of sensors are used for proximity switching, speed detection, positioning and current sensing applications.

• The sensor operates like an analog transducer, thus directly returning a voltage.

• Its distance from the Hall plate can be determined with a known magnetic field.

Hall effect magnetic proximity sensor IC

• By using groups of Hall Effect sensors, the relative position of the magnet can be determined.

• The electricity which is carried through a conductor will produce a magnetic field which varies according to the current.

• The sensor can be used in order to measure the current without interrupting the circuit.

• The sensor is typically integrated with a permanent magnet or a wound core that surrounds the conductor to be measured.

Hall probe

• A Hall probe contains an indium compound semiconductor crystal such as indium antimonide, mounted on an aluminum backing plate, and encapsulated in the probe head.

• The plane of the crystal is perpendicular to the probe handle.• Connecting leads from the crystal are brought down through

the handle to the circuit box.

Pira DCS # 5M10.10Equipment:Magnet Hall Probe Ballistic Galvanometer6V Battery Wires

Hall switches:

• Hall switches (switching sensors) have an integrated comparator with predefined switching points and a digital output which can be adapted to different logic systems (Latched, Unipolar, Bipolar, Unipolar with inverted output, etc.).

• All Hall switches include an open-drain output transistor and require an external pull-up resistor to the supply voltage.

• A standard Hall switch has a single Hall plate and can respond to the absolute value of the magnetic field perpendicular to the plate.

• The Hall switch is characterized by the magnetic switching points BON (or BOP ) and BOFF (or BRPN). If the magnetic flux exceeds BON , the output transistor is switched on; if it drops below BOFF, the transistor is switched off. The magnetic hysteresis BHYS is the difference between the switching points BON and BOFF.

Switch/Latch Hall sensor

Outputamp

Comparator

Hall Sensor System overview

Input switches

Input amp

LPF Signal

recovery

OUTPUTINTERFACE

FRONT END BACK END

Linear Hall sensor

Most of the offset, noise and sensitivity problems are here!!!

QUADS

Cell offset reduced to +/- 100uv

Current spinning

Cell offset reduced to almost zero

How we reduce Hall cell offset ?

+

+

+

+

-

-

-

-

Static Techniques (QUADS)

• CELL Offset is spatially averaged, thus highly reduced

• Residual offset depends on individual offset contribution mismatches

Dynamic Techniques (current spinnig)

+

-

Phase 0

+

-

Phase 90

Offset from each single cell can be as high as 10mv!!!

How we reduce Hall cell noise ?

d

nHI Ntq

rISS

Current driving (CD)

- At room temp SNR is worse than VD- At 150C is the same as VD- Sensitivity linearity over temp is better

Voltage driving (VD)

-At room temp SNR is better than CD-At 150C is the same as CD-Sensitivity over temp is parabolic

d

n

H

HI Ntq

r

R

VSS

How we reduce INPUT AMPLIFIER offset ?

AUTOZEROING

Offset Trimming

CHOPPING

(the way to go)

Residual offset of chopping….how we reduce it?

Some results from the actual world - offset

VSH IS ON

DC OFFSET

Out

put r

efer

red

(G=1

15x)

CHOPPER-STABILIZED AMP Residual OFF=F(fck)

0

100

200

300

400

500

600

700

1000800600400200100

freq [KHz]

Res

off ][

mv]

Unit 1 Unit 2 Unit 3 Unit 4 Unit 5

Ripple (modulated offset)1MHz 800KHz 600KHz

400KHz 200KHz 100KHz

Some results from the actual world – ripple

Some results from the actual world – noise (1)

1/f reduction

~ 90nv/Hz

fk ~ 2KHz

INPUT

FLICKER NOISE

POST-CH

LPFCHOPPER

f ffCK

However…• How do we ADD amplifier + Hall Cell offsets ?• What freq do we chop at ?• What about noise modulation ?• What about the LPF recovery system ?

– Is it too large ? Too much delay ?

• For many years Patented technique SH RECOVERY was used.• NO LPF (but Sinc Filter) , No delay. but Aliasing Noise.

• Just now new ideas are being developed to use Topologies that combine no LPF with low noise amplifiers (aliasing free).

Goal was to obtain a relaxed LPF, with small area and delay

Chopper with SH Recovery First DOC FE improvement: SH RECOVERY chopper (1995 – DB2)

Vsig

Voff

A

5fBW

HCK

LPF

10)(OSR pole-1

/ 3

dBCK ffOSR

Vsig

Voff

Vsig

Voff

Demodulation + S&H

Chopper Amplifiers

Results of experiments:

- Hall cell : Current spinning allows to separate Hall cell offset from signal offset or signal could be modulated (chopped)

- Input Amplifier:

- Chopping is the most suited DOC technique for high accuracy (low offset, low noise) systems

+ Totally removes 1/f noise and offset

- Limits amplifier bandwidth

- SH RECOVERY

+ Helps reduce delay with small area

- Introduces aliasing

- Hall Cell and Amplifier offset can be added in the base band while the signal is modulated.

We have the signal … now what ?

• Offset was reduced, Gain stabilized over temp… what else ?

• Process Variations & Application errors Trimming.– Needs to be NON-VOLATILE memory. Poly fuses.

• Bank of fuses to affect analog parameters (Gain, Sens, etc)• Can also be EEprom … but 150C is a problem.

• Output the signal What format ?– Binary (H or L)… if B>Bop , Vout = L or B<Brp , Vout = H // Bop-Brp=Bhy– Linear … requires output amplifier (class A or AB), Ro < 10ohm.– Digitized , need a AD converter. High resolution (12bit)… sigma-delta.

Application of Hall effect based sensors

• Hall Effect Switches Unipolar Switches Bipolar Switches• Hall Effect Fan Motor Drivers• Hall Effect Latches• Linear Hall ICs• Special-Purpose Hall ICs• Triaxis® Hall ICs

Hall Effect SwitchesMLX92241The device integrates a voltage regulator, Hall sensor with advanced offset cancellation system, programmable digital logic and a current sink-configured output driver, all in a single package .

Uses:-Bop- Brp- Hysteresis- Temperature Compensation- Active Pole- Output Polarity

Features and Benefits:• MLX92241 Features and Benefits• Wide operating voltage range: from 2.7V to 24V• Very wide range for magnetic sensitivity• Chopper-stabilized amplifier stage• Programmable negative temperature coefficient• Reverse Supply Voltage Protection• Under-Voltage Lockout Protection• Thermal Protection• High ESD rating / Excellent EMC performance• Thin SOT23 3L Green Compliant package• Factory Programmable magnetic switching thresholds (Bop, Hyst, TC)

Hall Effect Unipolar SwitchesMLX92221The device integrates a voltage regulator, Hall sensor with advanced offset cancellation system, programmable digital logic and a current sink-configured output driver, all in a single package.Uses:-Bop- Brp- Hysteresis- Temperature Compensation- Active Pole- Output Polarity

Features and Benefits:• Wide operating voltage range: from 2.7V to 24V• Very wide range for magnetic sensitivity• Chopper-stabilized amplifier stage• Programmable negative temperature coefficient• Reverse Supply Voltage Protection• Under-Voltage Lockout Protection• Thermal Protection• High ESD rating / Excellent EMC performance• Thin SOT23 3L Green Compliant package• Factory Programmable magnetic switching thresholds (Bop, Hyst, TC)

Hall Effect Unipolar SwitchesMLX92241 The device integrates a voltage regulator, Hall sensor with advanced offset cancellation system, programmable digital logic and a current sink-configured output driver, all in a single package.

Uses:-Bop- Brp- Hysteresis- Temperature Compensation- Active Pole- Output Polarity

Features and Benefits:• Wide operating voltage range: from 2.7V to 24V• Very wide range for magnetic sensitivity• Chopper-stabilized amplifier stage• Programmable negative temperature coefficient• Reverse Supply Voltage Protection• Under-Voltage Lockout Protection• Thermal Protection• High ESD rating / Excellent EMC performance• Thin SOT23 3L Green Compliant package• Factory Programmable magnetic switching thresholds (Bop, Hyst, TC)

Hall Effect Bipolar SwitchesUS2881The device integrates a voltage regulator, Hall sensor with dynamic offset cancellation system, Schmitt trigger and an open-drain output driver, all in a single package.

-The device is delivered in a Thin Small Outline Transistor (TSOT) for surface mount process and in a Plastic Single In Line (TO-92 flat) for through-hole mount.-Both 3-lead packages are RoHS compliant.

Features and Benefits:• Wide operating voltage range from 3.5V to 24V• Very high magnetic sensitivity• CMOS technology• Chopper-stabilized amplifier stage• Low current consumption• Open drain output• Thin SOT23 3L and flat TO-92 3L both RoHS Compliant packages• SE package North Pole Active• UA package South Pole Active

Hall Effect Fan Motor Drivers

MLX90283The MLX90283 is a one-chip solution for driving single-coil brushless DC vibration motors.

Designed in mixed signal CMOS technology, the device integrates Hall sensor with dynamic offset cancellation, control logic and full bridge output driver.

The device is delivered in an Ultra Thin QFN package. Its 0.4mm thickness enables thin and competitive vibration motor design.This 6-pin leadless package is RoHS compliant.

Features and Benefits:• Low supply voltage: 1.8V ~ 3.6V• Low current consumption• Active Start (proprietary design to address Dead Point issue)• High motor efficiency• High sensitivity Hall sensor• Full Bridge output driver• Reverse voltage protection• Thermal Protection• Ultra thin leadless RoHS compliant package• No external components

Hall Effect Fan Motor Drivers

MLX90285The MLX90285 is a really cool driving solution for silent brushless cooling fans. It provides a robust, high performance and fully integrated Hall effect based fan driver IC, including technology lowering both acoustic and electrical noise. This device is ready to serve demanding cooling requirements in office equipment or consumer electronics such as Laser Printers, Projectors or Flat-Screen Televisions.

Features and Benefits:• 2-coil fan driver• Wide Operating Voltage range: from 5V to 24V• 1-chip solution: Hall element + Output Drivers• Soft Switching for Low Noise : Acoustic & Electrical• Active Slope Control without external components• - automatically adapts slope to rotation speed• Two-Stage Thermal Protection• Locked Rotor Protection and auto-restart• Output options:• - Tachometer open drain output (MLX90285-FG)• - Alarm open drain output (MLX90285-RD)• “Green” Compliant Package options:• - Available in 4-pin through-hole VK (“No-VDD” design)• - surface mount SOIC8• Pin-to-pin compatible with US90A & US91A

Hall Effect Fan Motor Drivers

US168The use of Melexis Soft Switching concept lowers the acoustic and electrical motor noise and provides smoother operation.The device is also provided in a Chip Scale Package, the smallest packaged IC configuration available. The CSP saves valuable PCB and housing space allowing smaller integration. The footprint of the new Ultra-Thin QFN (Quad Flat No leads) package is only 3mm2 (1.5 x 2mm) with 0.43mm maximum thickness.

Features and Benefits:• Soft switching for low noise• Low supply voltage: 1.8V to 6.5V• Full bridge driver• High sensitivity integrated Hall sensor• Low power consumption• Reverse voltage protection• Locked rotor protection and auto-restart• Thermal protection and auto-restart• No external components needed• Tachometer output signal (FG)• Thin SOT23-5L RoHS compliant package• Ultra thin leadless UTQFN-6L RoHS compliant package.

Hall Effect Two-Coil Fan Motor Drivers

US890Based on the advanced Melexis CMOS process, the IC contains a Hall-effect sensor, dynamic offset correction and powerful output drivers with 1200mA peak output current capability.

Specially designed for driving large fans, the device is optimized for low start-up voltage.

The Frequency Generator open-drain output makes easier the connectivity with any external interface such as hardware monitoring or Super I/O IC.

Features and Benefits:• Peak output current up to 1200mA• Low start-up voltage• Low output resistance• High sensitivity integrated Hall Sensor• Power-efficient CMOS and power MOSFETs• Built-in output protection clamping diode• Locked rotor protection and auto-restart• Integrated tachometer signal protected output• Low cost• 2-coil fan driver with FG output in• RoHS Compliant 4-pin VK package

Hall Effect Latches

US890The MLX90224 series are dual Hall effect latches. It includes two Hall effect latch functions of which typical thresholds are +/- 2.0 mT. In each latch, the magnetic flux detection is performed by a switched silicon Hall plate. The BOP and BRP are temperature-compensated and give a sensitivity temperature coefficient of 500 ppm/oC to compensate popular magnets.The output will be latched off (BRP) in the presence of aNorth field. Spacing on the plates is 1.85mm. The MLX90224 B series are designed for direction detection with a high speed chopper which provides 15ms delay.

Features and Benefits:• Chopper Stabilized Amplifier Stage• CMOS for Optimum Stability, Quality and Cost• Dual Output 4.5V to 26V Operation• Phase/Direction Detection (B)

Hall Effect Latche- Low Voltage & High Sensitivity

US3881 The device integrates a voltage regulator, Hall sensor with dynamic offset cancellation system, Schmitt trigger and an open-drain output driver, all in a single package.The low operating voltage and extended choice of temperature range make it suitable for use in automotive, industrial and consumer low voltage applications.The devices are delivered in a Thin Small Outline Transistor (TSOT) for surface mount process and in a Plastic Single In Line (TO-92 flat) for through-hole mount.Both 3-lead packages are RoHS compliant.• Features and Benefits:• Operating voltage range from 2.2V to 18V• High magnetic sensitivity – Multi-purpose• CMOS technology• Chopper-stabilized amplifier stage• Low current consumption• Open drain output• Thin SOT23 3L and flat TO-92 3L both RoHS Compliant packages• SE package North Pole Active• UA package South Pole Active

Linear Hall ICs

MLX90242 The MLX90242 is a CMOS Linear Hall Effect sensor IC. It possesses active error correction circuitry which virtually eliminates the offset errors normally associated with analog Hall Effect devices.

The ratiometric output voltage is proportional to the supply voltage. When using the supply voltage as a reference for an A/D converter, fluctuations of +10% in supply voltage will not affect accuracy.The voltage at the output will increase as a South magnetic field is applied to the branded face of the MLX90242. A North magnetic field will cause it to decrease. In the SOT-23 package the behavior is reversed. A North field will increase and a South field decrease the output voltage.

Features and Benefits• Small Plastic Package (SOT-23, TO-92)• Quad Switched Hall Plate / Chopper Stabilized Amplifier• Ratiometric Output for A/D Interface• Low Quiescent Voltage Thermal Drift

SMD Programmable Linear Hall Sensor IC

MLX90292 MLX90292 is a SMD Programmable Linear Hall Sensor IC with digital output dedicated for position sensor applications with high safety requirements and/or small data latency.

The measured magnetic flux density is conditioned through a fast DSP and reported through a digital communication channel feat. a 2-wire PAS4, PSI5 or PWM as well as 3-wire PWM mode. Latency time is less than 500 us.

The MLX90292 is available in TSSOP-16 package feat. 2 independent and isolated dies for redundancy purpose.

• MLX90292 Features and Benefits• Programmable Hall effect sensor• > 12-bit magnetic flux density• > 8-bit temperature (PAS4 & PSI-5)• > Extensive diagnostic• > Embedded µ-controller• > Piecewise linearization• 2-/3-Wire PWM Mode (up to 2kHz)• Dual die for redundancy (safety)• Measurement range from ±30mT to ±170mT• Programmable through the connector• Dual customer area for supply chain split• Over 48 bit customer IDs available• TSSOP16 SMD package RoHS compliant• Lead free component, suitable for lead free soldering profile 260°C

Special-Purpose Hall ICsDifferential Dynamic Hall Effect Sensor:

MLX90254 The MLX90254 is a Differential Dynamic Hall Effect Sensor which has been developed for automotive crankshaft and ABS (anti-lock brake system) applications. The IC, combined with a magnet placed at his back, offers speed and position sensing of ferromagnetic tooth-wheels in dynamic operation (non zero speed). Its low hysteresis enables it to operate over a wide range of airgaps from -40°C to 150°C.

The output structure is an Open-Drain NMOS transistor with a capability of 25 mA under 24V and protected against short-circuits. The IC is packaged in 4-SIP VA.

• MLX90254 Features and Benefits• Differential hall sensor• Low consumption• Excellent repeatability performance• Large airgap range• Large supply voltage range• Distance between Hall plates : 2.25 mm

Programmable high speed Hall effect sensor IC

MLX91209 The MLX91209 is a fully customer-programmable monolithic Sensor IC packaged in standard SIP package. The Hall Sensor provides a high speed analog output signal proportional to the external applied flux density. The MLX91209 enables the user to construct a precise current sensor solution with fast response time of 3µs.

The MLX91209 sensor is automotive qualified and particularly appropriate for DC and/or AC current measurements up to 200kHz with galvanic isolation, fast response time and small package size.The MLX91209 features over voltage and reverse voltage protection including diagnostics. The transfer characteristic of the MLX91209 is fully customer programmable (offset, sensitivity and response time).

Current Sensor ApplicationsIn the typical application the sensor is used in combination with a ring shaped soft ferromagnetic core. The Hall-IC is placed in a small air gap and the current conductor is passed through the inner part of the ferromagnetic ring. The ferromagnetic ring concentrates and amplifies the magnetic flux on the Hall-Sensor IC which generates an output voltage proportional to the current. The Melexis MLX91209 is especially well suited for applications requiring very fast response time such as inverters. It can be used in many different fields such as electrical or hybrid vehicles, solar panels, etc.

Product Versions•

MLX91209BA - programmable magnetic sensitivity: 10 to 150mV/mTMLX91209CA – programmable magnetic sensitivity: 5 to 150mV/mT

• MLX91209 Features and Benefits• Programmable high speed current sensor• Fast response time < 3µs• Large bandwidth DC–200kHZ• Fast analog output (12 bits resolution DAC)• Selectable ratio-metric output• 48 bit ID number• Single die SIP (VA) package, RoHS compliant• Lead free component, suitable for lead free soldering, MSL3

Triaxis: The Sky's The LimitTriaxis® is Melexis’ trademarked term to describe an innovative magnetic sensor technology capable of 3 axis magnetic field measurement from a single sensor. Triaxis® technology used to measure the position of a magnet very precisely. It can be used to measure rotational, linear and 3D displacement as well as sense current flowing in a wire. It measures the properties of a magnetic field using the Hall Effect and innovative, patented, flux concentrators, known as "Integrated Magnetic Concentrators" or IMC.

Depositing a patented magnetic film to the surface of our IC and applying a specific mathematical formula to the resulting signals we can, with the same sensor, measure 3 components (x,y and z) of the applied magnetic flux density. Conventional Hall sensors (including devices like our MLX90215 Programmable Linear Hall Sensor) are only sensitive to flux in 1 axis, through the sensor.

Triaxis Features and Benefits• Triaxis® Magnetometer (BX, BY, BZ)• On Chip Signal Processing for Robust Position Sensing• High Speed Serial Interface • Enhanced Self-Diagnostics Features• 5V and 3V3 Application Compatible• Immune to dirt and dust• Assembly Misalignment Tolerant• Inexpensive magnet capability• Single Die – SO8 Package RoHS Compliant• Dual Die (Full Redundant) – TSSOP16 Package RoHS Compliant

Triaxis Programmable Position Sensor IC featuring SPI

MLX90363 General DescriptionUniversal, maximum flexibility for applications development can be accomplished with the MLX90363. Designed to be paired with an off-the-shelf microcontroller, the MLX90363 relies on SPI output communication. The range of position sensing applications are limitless and constrained only by the imagination of the designer. This puts the Bx, By and Bz information directly accessible for processing by the embedded microcontroller. Data from the on chip temperature sensor and from the internal chip diagnostics can also be digitally transmitted. Programming happens through the same channel.

• MLX90363 Features and Benefits• Triaxis™ Magnetometer (BX, BY, BZ)• On Chip Signal Processing for Robust Position Sensing• High Speed Serial Interface (SPI compatible – Full Duplex)• Enhanced Self-Diagnostics Features• 5V and 3V3 Application Compatible• 14 bit Output Resolution• 48 bit ID Number• Single Die – SO8 Package RoHS Compliant• Dual Die (Full Redundant) – TSSOP16 Package RoHS Compliant

MLX91206The MLX91206 opens new opportunities for contactless current sensing in renewable energy applications, Hybrid Electric Vehicle (HEV) and Electric Vehicle (EV). The device is a customer programmable monolithic Sensor IC featuring the Triaxis Hall technology. It enables the user to construct small, economical current sensor solutions with fast response times. The chip directly monitors the current flowing in an external conductor such as a bus bar or PCB track.

MLX91206 Features and Benefits• Programmable high speed current sensor• Fast response time• Large bandwidth DC– 90kHZ• Magnetic concentrator (IMC) provides higher Signal to Noise Ratio• Over voltage and reverse polarity protection• Broken track diagnostic• Fast analog output (12 bits resolution DAC)• PWM output (12 bits resolution ADC)• Selectable ratio-metric output• Thermometer output• Programmable switch function• 17 bit ID number• Single die SOIC8 package RoHS compliant• Lead free component, suitable for lead free soldering, MSL3

References: Links:• https://www.google.co.in/• http://en.wikipedia.org/• http://en.wikipedia.org/wiki/Hall_effect_sensor• http

://lcr.uns.edu.ar/electronica/Posgrado/EAMTA/2006/Documents/Analogicos/Smart%20HE%20Sensors%20over%20Regular%20Processes%20-%20part%201.ppt

• http://sensing.honeywell.com/index.php?ci_id=47847• http://

www.allegromicro.com/Design-Center/Technical-Documents/Hall-Effect-Sensor-IC-Publications/Integrating-Hall-Eff

• http://www.melexis.com/Products-By-Category/Hall-Effect-Sensor-ICs-1.aspx

Books:N.W. Ashcroft and N.D. Mermin "Solid State Physics“ T. Ohgaki et al. "Positive Hall coefficients obtained from contact misplacement on evident n-type ZnO films and crystals“Robert Karplus and J. M. Luttinger (1954). "Hall Effect in Ferromagnetics". Phys. Rev. 95: 1154–1160.N. A. Sinitsyn (2008). "Semiclassical Theories of the Anomalous Hall Effect“