Hall-Effect Latch for High Temperature Operation
A1225, A1227
and A1229
10
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 4. Chopper stabilization technique
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 sen-
sor IC. 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. Allegro
employs a technique to remove 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 base band, 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 sensor IC while completely removing
the modulated residue resulting from the chopper operation. The
chopper stabilization technique uses a high-frequency sampling
clock. For the demodulation process, a sample-and-hold tech-
nique 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.
Amp
Regulator
Clock/Logic
Hall Element
Tuned
Filter
Anti-Aliasing
LP Filter
