A1225, A1227
and A1229
Hall Effect Latch for High Temperature Operation
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.
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 patented technique to remove key sources of the out-
put drift induced by thermal and mechanical stresses. This offset
reduction technique is based on a signal modulation-demodula-
tion 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
Regulator
Clock/Logic
Hall Element
Amp
Anti-Aliasing
LP Filter
Tuned
Filter
Figure 4. Chopper stabilization technique
Allegro MicroSystems, Inc.
115 Northeast Cutoff
10
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
SANKEN [ SANKEN ELECTRIC ]
