Linear Hall Effect Sensor ICs with Analog Output

A1324, A1325,

and A1326

9

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Amp

Regulator

Clock/Logic

Hall Element

Tuned

Filter

Anti-Aliasing

LP Filter

Concept of Chopper Stabilization Technique

Typical Application Circuit

Chopper Stabilization Technique

When using Hall-effect technology, a limiting factor for

switchpoint accuracy is the small signal voltage developed across

the Hall element. This voltage is disproportionally small relative

to the offset that can be produced at the output of the Hall IC.

This makes it difficult to process the signal while maintaining an

accurate, reliable output over the specified operating temperature

and voltage ranges. Chopper stabilization is a unique approach

used to minimize Hall offset on the chip. Allegro employs a

patented technique to remove key sources of the output drift

induced by thermal and mechanical stresses. This offset reduc-

tion technique is based on a signal modulation-demodulation

process. The undesired offset signal is separated from the

magnetic field-induced signal in the frequency domain, through

modulation. The subsequent demodulation acts as a modulation

process for the offset, causing the magnetic field-induced signal

to recover its original spectrum at baseband, while the DC offset

becomes a high-frequency signal. The magnetic-sourced signal

then can pass through a low-pass filter, while the modulated DC

offset is suppressed. In addition to the removal of the thermal and

stress related offset, this novel technique also reduces the amount

of thermal noise in the Hall IC while completely removing the

modulated residue resulting from the chopper operation. The

chopper stabilization technique uses a high frequency sampling

clock. For demodulation process, a sample-and-hold technique

is used. This high-frequency operation allows a greater sampling

rate, which results in higher accuracy and faster signal-processing

capability. This approach desensitizes the chip to the effects

of thermal and mechanical stresses, and produces devices that

have extremely stable quiescent Hall output voltages and precise

recoverability after temperature cycling. This technique is made

possible through the use of a BiCMOS process, which allows the

use of low-offset, low-noise amplifiers in combination with high-

density logic integration and sample-and-hold circuits.

GND

1[1]

3[2]

Pin numbers in brackets

refer to the UA package

2[3]

VOUT

A132x

VCC

V+

0.1 μF