A1171EEWLT-P 데이터 시트보기 (PDF) - Allegro MicroSystems

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A1171EEWLT-P

Micropower Ultrasensitive Hall Ef fect Switch

Allegro MicroSystems 

A1171

Micropower Ultrasensitive Hall Effect Switch

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 element. This makes it difficult to process the signal while

maintaining an accurate, reliable output over the specified oper-

ating temperature and voltage ranges.

Chopper stabilization is a unique approach used to minimize

Hall offset on the chip. The patented Allegro technique, namely

Dynamic Quadrature Offset Cancellation, removes key sources

of the output drift induced by thermal and mechanical stresses.

This offset reduction 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 mag-

netic sourced signal then can pass through a low-pass filter,

while the modulated dc offset is suppressed. This configuration

is illustrated in figure 4.

The chopper stabilization technique uses a high frequency clock.

For demodulation process, a sample and hold technique is used,

where the sampling is performed at twice the chopper frequency.

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.

The repeatability of magnetic field-induced switching is affected

slightly by a chopper technique. However, the Allegro high

frequency chopping approach minimizes the affect of jitter and

makes it imperceptible in most applications. Applications that

are more likely to be sensitive to such degradation are those

requiring precise sensing of alternating magnetic fields; for

example, speed sensing of ring-magnet targets. For such applica-

tions, Allegro recommends its digital device families with lower

sensitivity to jitter. For more information on those devices,

contact your Allegro sales representative.

Regulator

Hall Element

Clock/Logic

Amp

Figure 4. Chopper Stabilization Circuit (Dynamic Quadrature Offset Cancellation)

Allegro MicroSystems, LLC

8

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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