A1160 Datasheet, PDF (11/13 Pages) Allegro MicroSystems – Chopper-Stabilized Precision Hall Effect Switch With Advanced Diagnostics

A1160
Chopper-Stabilized Precision Hall Effect Switch
With Advanced Diagnostics
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 across the specified operating tempera-
ture 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 unwanted 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. This configuration is illus-
trated in figure 4.
The chopper stabilization technique uses a 400 kHz, high
frequency clock. For demodulation process, a sample-and-hold
technique is used, where the sampling is performed at twice the
chopper frequency (800 kHz). This high-frequency operation
allows a greater sampling rate, which results in higher accuracy
and faster signal-processing capability. This approach desensi-
tizes 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.
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 applications, Allegro
recommends its digital sensor IC families with lower sensitivity
to jitter. For more information on those products, contact your
Allegro sales representative.
Regulator
Hall Element
Clock/Logic
Amp
Low-Pass
Filter
Figure 4. Chopper stabilization circuit (Dynamic Quadrature Offset Cancellation)
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