A1308 and
A1309
Linear Hall-Effect Sensor ICs with Analog Output
Available in a Miniature, Low-Profile Surface-Mount Package
APPLICATION INFORMATION
A1308
A1309
VOUT
VCC
RL
4.7 nF
GND
0.1 µF
5 V
Figure 5: Typical Application Circuit
through a low-pass filter, while the modulated DC offset is sup-
pressed. In addition to the removal of the thermal and mechanical
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 demodulation process, a sample-and-hold technique
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-
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 sensor
IC. This makes it difficult to process the signal while maintain-
ing 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 baseband, while the DC offset becomes a
high-frequency signal. The magnetic-sourced signal then can pass density logic integration and sample-and-hold circuits.
Regulator
Clock/Logic
Hall Element
Amp
Anti-aliasing Tuned
LP Filter
Filter
Figure 6: Chopper Stabilization Technique
Allegro MicroSystems, LLC
115 Northeast Cutoff
9
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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