A1220 ALLEGRO [Allegro MicroSystems], A1220 Datasheet - Page 10

• Manufacturer Part Number: A1220
• Description: Chopper Stabilized Precision Hall Effect Latches
• Manufacturer: ALLEGRO [Allegro MicroSystems]

A1220, A1221
and A1222
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 ele-
ment. This makes it difficult to process the signal while main-
taining 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. 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 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 2.
Hall Element
Figure 2. Model of chopper stabilization technique
Chopper Stabilized Precision Hall Effect Latches
Regulator
The chopper stabilization technique uses a 400 kHz high fre-
quency 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 device families with lower sensitivity
to jitter. For more information on those devices, contact your
Allegro sales representative.
Clock/Logic
Amp
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
Low-Pass
Filter
10