principle of the hall effect · pdf fileprinciple of the hall effect sensor z when a...

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ChenYang Technologies GmbH & Co. KG

Principle of the Hall Effect Sensor

When a conductor carrying a current (I) is placed in a magnetic field (B) and oriented so that the current and magnetic filed are at right angles, an electric field is produced in the conductor at right angles to both current and magnetic field and produce a Hall Voltage (Vh) given by:

Vh = Kh . B . I

e.n.thK1=

Where the sensitivity Kh is given by: t: Thickness n: Electron concentration e: Electron charge

BZ I

t Jy

Jx

Vh

L

w

Hall Effect phenomenon



Magnetic Field Sensors Spectrum

Commercial GaAs Hall effect sensor

Magnetoresistors

Inductive sensors

Giant magnetoresistors

Nuclear magnetic resonance

Fluxgate magnetometer

SQUIDs

10-6 10-3 10-2 10-1 1 10 102 103 104 105 Gauss 10-10 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 Tesla

Magnetic field sensor spectrum

Magnetodiode

Magneto-optical sensor

Optically pumped magnetometer

Nuclear precession magnetometer

Fibre optic magnetometer

AHS 2DEG Hall effect sensor

Earth's field



Hall Effect Devices Parameters

Offset Voltage: The Piezoresistance Effect Misalignment.

Noise

- 1/f Noise - Thermal noise

Self Induced Magnetic Field By the passage of the applied current

Frequency Limitation Restricted by relaxation time of the dielectric

Sensitivity Current sensitivity Si

Voltage sensitivity Sv

Linearity

Effect of Temperature The Joule Heating Ambient temperature

IBVS h

i =

GLwS hv µ=



Epitaxial Layer Profiles and Processing

Generic Hall effect epitaxial structure

In the form of square Greek crosses with an (L/w) ratio of 3

GaAs Buffer layer

InyGa(1-y) As Quantum Well

Silicon δ layer

AlxGa(1-x) As Spacer layer

AlxGa (1-x) As Supply layer

GaAs cap Layer • The device structure was

symmetrical and thus input and output resistance were the same.

• Au-Ge-Ni ohmic contacts aree used

• Packaged into SOT-143.

L

Greek cross

Ohmic contact

L

W

W = 70 µm L = 210 µm

Shape of the 2DEG Hall sensor



The manufacturing Process

Lithography

Etching

Annealing

Metal Evaporation

Packaging

Stage 2 - Processing Stage 3 - PackagingStage 1- Epitaxial Growth

Contact Layer Charge Supply Layer Quantum Well Layer

Buffer Layer GaAs Substrate



Characteristics of the 2DEG Hall Sensors

5x10112x1012Channel sheet carrier density (n) (cm-2)

0.25 7000 200

1.4 6500

50

Power consumption for Vin = 1 V (mW) Electron mobility (µH) (cm2/V.sec) AlGaAs Spacer layer (Å)

0.3 0.3 Resistance drift over temperature (%/°C)

- 0.08 - 0.08 Current sensitivity drift over temperature (%/°C)

-100 to +180 -100 to +180Operating temperature (°C)

1000 200 Current sensitivity (V/AT)

4000 680 Output resistance (Ω)

4000 680 Input resistance (Ω)

1 1.5 Nominal Control Current (mA)

P15 P2 Parameter



Noise Measurement

• From DC to 1 kHz the initial noise is reduced by 55 dB.

• To eliminate the low

frequency noise, the Hall sensor has to be driven by an AC current with a frequency higher or equal to 1 kHz

dB

-120-110-100-90-80-70-60-50

Hz50 1025.10

210

45.10

42.10

3

P15P2

1/f

-130

-140

dB

-120-110-100-90-80-70-60-50

Hz50 1025.10

210

45.10

42.10

3

P15P2

1/f

-130

-140

Noise measurement of the P2 and P15 Hall sensors for an input voltage Vin = 1V



Automatic Offset Cancellation

The automatic offset cancellation

technique uses a symmetric Hall plate.

The quadrature states are generated by periodically connecting the supply current and the signal conditioner input.

Each state is defined by the state of the

clock which controls the switches.

At the output of the switched Hall plate a low pass filter averages out the offset voltage

Contact commutation

switches

Low passfilter

Amplifier I

Hall plate

Vout

Block diagram of the switched Hall plate

Clock generator



Offset Cancellation Circuitry

Switched Hall plate for automatic offset cancellation

HP

I

VH - Voffset (0°)

VH + Voffset (90°) I

Equivalent circuit for a positive CK

HP

1

4 2

3

1 4 2

3

Sw6

Sw7 CK

CK

Sw

Sw1 Sw2

Sw3 Sw4

Sw8

I

CK

Instrument Amplifier

1 4 2 3

HP

- +

Sw3



DC Circuit Design

Instrumentation Amplifier, G = 103

DC Current Sourc

Low Pass Fc = 0.1

Amplifier

G = 20

DVM

Switching

circuit

Hall plate

Square wave

1 kHz

Power supply ±5V

Block diagram of the DC Hall effect magnetometer circuit

Current source.

Switching circuit for automatic offset cancellation.

Low noise instrumentation amplifier,

with a gain of one thousand.

Low pass active filter with a cut-off frequency of 0.1 Hz.

Amplifier based on a low noise,

precision operational amplifier, with a gain of twenty.

Overall gain of the circuit equal to

20.103.



Test Circuit of the Magnetometer

Helmholtz coil driving

circuitDC/AC

magnetometer circuit

Digital voltmeter

Hallsensor

Helmholtz coil Fluxgate

sensor


controller

Helmholtz coil driving

circuitDC/AC

magnetometer circuit

Digital voltmeter

Hallsensor

Helmholtz coil Fluxgate

sensor


controller

Test Circuit Arrangement



Offset Cancellation for DC Circuit

Output signals of the DC circuit low pass filter using the P2 Hall sensor, (a) with offset cancellation and (b) without offset cancellation.

m0. 1.0 2.0 3.0 4.0 5.0-200-160-120

-80-40

04080

120

160200

O

ffset

vol

tage

(mV

)

Time (ms)

(b) (a)



DC Circuit Measurement

The magnetic sensitivity of the

circuitry using the P15 sensor is equal to 5 mV/µT. the resolution was 4 µT.

Using the P2 with the same overall magnetic sensitivity, the resolution was 1 µT.

Hall voltage versus magnetic induction and the corresponding fluctuation from the P15 and P2 2DEG Hall sensors, with a bias voltage of 1V.

-

-

-

-

-

30

80

13

18

- - - - 0 10 20 30 4

Magnetic field (µT)

Out

put v

olta

ge (m

V)

P2A P15A



AC Circuit Design

AC current source. Offset cancellation circuit. An instrumentation amplifier,

with a gain of one thousand. A low pass active filter (LPF)

with a cut-off frequency of 1 kHz.

An amplifier based on a low noise, precision operational amplifier with a gain of fifty-six.

A phase shifter was introduced to make the input signal of the PSD in phase with a reference signal.

A PSD, which acts as a very high Q pass band filter.

A low pass filter.

ReferenceSignal

Phase Shifter

Low-PassFilter

fc = 0.1 Hz

Phase Sensitive

DemodulatorDigital Volt

Meter

AmplifierG = 56

InstrumentationAmplifier G = 103

Multivib-rator

10 kHz

Commut-ation

Network

Power Supply ± 5VSinewave Oscillator

1 kHz

LPFfc = 1 kHz

SchmittTrigger

Hall

Sensor

Current Source

Block diagram of the AC Hall effect magnetometer circuit



AC Circuit Offset Cancellation

Output waveform of the AC circuit instrumentation amplifier, (a) with and (b) without offset cancellation, using the P2 Hall sensor.

(b) X: 0.5 ms/Div Y: 0.5 mV/Div

(a) X: 0.5 ms/Div Y: 0.02 mV/Div



AC Circuit Measurement

Using the P2 Hall sensor with a

sensitivity of 14 mV/µT the minimum detectable magnetic field with the AC magnetometer is equal to 100 nT.

The resolution obtained is 40 times lower than, and amongst the lowest ever reported using a GaAs Hall effect sensor with low cost signal conditioning circuitry.

-250

-200

-150

-100

-50

0

50

100

150

200

250

-20 -15 -10 -5 5 10 15 20

Out

put v

olta

ge (m

V)

Magnetic field (µT)-250

-200

-150

-100

-50

0

50

-250

-200

-150

-100

-50

0

50

100

150

200

250

-20 -15 -10 -5 5 10 15 20

Out

put v

olta

ge (m

V)

Magnetic field (µT)

Output voltage of the AC circuit versus variable magnetic field using P2 Hall sensor



Magnetic Field Mapping

The magnetic field mapping was performed using a scanner assembly, which comprises:

The scanner comprises Two X and Y stepper motor drive units, capable of positioning the sensor at any point within a 200 x 150 mm area to a resolution of 50 µm on the Y axis and 25 µm on the X axis.

The scanner is driven by the parallel port of a personal computer (PC), which include the National Instruments LabVIEW software.

The Hall sensor transmits signal voltages to the DC circuit described previously.

The reading is transmitted to a bipolar 12 bits analogue to digital converter (ADC).

The ADC in turn transfers the data to the host computer via the national instrument data acquisition card the PCI-6503 board.

The computer is used for storage display and signal processing of the digital data.

PC

Hall Sensor

Data acquisition system layout

PC

I -65

03

Conditioning AC/DC Circuit

ADC LTC1276

Photo- CouplerTLP521

TimerLM555

Buffer 74LS241

12 bit

Power Supply ±5V

DAQ board



PC

12 bits Analogue to Digital Converter

Bus Buffer

NI 24 Lines

Digital I/O Device

AC/DC Circuit N.I Labview

6.i

Parallel Port

X stepper motor

Y linear stepper motor

X-axis rail

Y-axis Lead screw

Sensor holder

Area to Scan

Limit switchs

4

131312

8

Clock

Optic Coupler

Digital Bus Analogue Bus

N Number of bit

Hall sensor

Stepper motors Powerdriver + switches drive

Hardware assembly of a magnetic scanning system

Magnetic Field Mapping



Data Acquisition Flowchart

Data acquisition flowchart

Open and enter the name of a new file

Initiate DAQ port for reading

Read data from DAQ port

No

Yes

Convert data from 2s complement into binary code

Convert data into decimal value

Display output voltage and the equivalent measured magnetic field

Save data into designated file

Close file

Report any error

Start

End

Data available from DAQ port

Stop data acquisition

Yes

No



Data Acquisition Program

Front panel of DAQ program



Scanning Software

Flowchart of the mapping program

Start

Open a new file where to store data

Enter (X,Y) lengths of the area to scan in (cm)

Enter the speed of the motors

Check the power supply. Initialise the DAQ port and the motors driver.

Calculate the number of steps (N X , N Y )

End of Y length

End of X length

Move one step Y

Store data in designated file

Read data from sensor

Save and close file

End

Report any errors

Move one step X

Invert X steps way

Start

Open a new file where to store data

Enter (X,Y) lengths of the area to scan in (cm)

Enter the speed of the motors

Check the power supply. Initialise the DAQ port and the motors driver.

Calculate the number of steps (NX, NY)

End of Y length

End of X length

Move one step Y

Store data in designated file

Read data from sensor

Save and close file

End

Report any errors

Move one step X

Invert X steps way

Yes

Yes

No

No



Scanning Software

Front menu of the scanning software



Filtering Data

Filtered data using a Schmitt trigger program



Bank Notes Scanning • Using the magnetic field

mapping system a £5 and £10 UK and €10 Euro bank notes were scanned.

• it was found that it generates a reading over the metal strip.

Scanning of £5, £10 UK and €10 bank notesover the metal strip

Processing of the scanned bank notes raw signals

Position



Floppy Disk Scanning

Floppy disk scan of an 5 x 5 mm2 area, the tracks of the disk are displayed as vertical lines.

Floppy disk scanning Cross section of the red line

Position



Hall Voltage vs.Magnetic Flux Density for various Commercial Hall Sensors

Ic=1 mA

500

450

400

350

300

250

200

150

100

50

0

Magnetic Flux Density B (mT)

Output Hall Voltage V (mV)

0 50 100 150 200 250 300 350 400 450 500

InSb

I10A

P15A

InAs

GaAs

CCoommppaarriissoonn wwiitthh LLeeaaddiinngg CCoommmmeerrcciiaall HHaallll SSeennssoorrss



0

20

40

60

80

100

120

140

25 50 75 100 125 150 175 200Output Hall Voltage VH (mV)

Pow

er D

issi

patio

n (m

W)

Blue and Orange new sensors

Hall Voltage vs.Magnetic Flux Density for various Commercial Hall Sensors Ic=1 mA

Commercial Hall Sensors



CONTACTS Technical Support: Dr J. Liu, ChenYang Technologies GmbH & Co. KG Email: [email protected] Tel: +49 (0)8121 -2574102 Local Sales Department: M.Sc. Jane Chen, ChenYang Technologies GmbH & Co. KG Email: [email protected] Tel: +49 (0)8121 -2574100 Fax: +49 (0)8121 -2574101 http://www.chenyang-gmbh.com http://www.cy-sensors.com http://www.hallsensors.de

principle of the hall effect · pdf fileprinciple of the hall effect sensor z when a...

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