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A3425 Datasheet(PDF) 7 Page - Allegro MicroSystems |
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A3425 Datasheet(HTML) 7 Page - Allegro MicroSystems |
7 / 21 page Ultra-Sensitive Dual-Channel Quadrature Hall-Effect Bipolar Switch A3425 7 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Functional Description Chopper-Stabilized 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 dis- proportionally small relative to the offset that can be produced at the output of the Hall device. This makes it difficult to process the signal and maintain an accu- rate, reliable output over the specified temperature and voltage range. Chopper stabilization is a unique approach used to minimize Hall offset on the chip. The patented Allegro technique, dynamic quadrature offset cancellation, removes key sources of the output drift induced by thermal and mechanical stress. This offset reduction technique is based on a signal modulation-demodula- tion process. The undesired offset signal is separated from the magnetically induced signal in the frequency domain through modulation. The subsequent demodu- lation acts as a modulation process for the offset, causing the magnetically-induced signal to recover its original spectrum at the baseband level, while the dc offset becomes a high-frequency signal. Then, using a low-pass filter, the signal passes while the modulated dc offset is suppressed. The chopper stabilization technique uses a 170 kHz high-frequency clock. The Hall element chopping occurs on each clock edge, resulting in a 340 kHz chop frequency. This high-frequency operation allows for a greater sampling rate, which produces higher accuracy and faster signal processing capability. This approach desensitizes the chip to the effects of ther- mal and mechanical stress. The disadvantage to this approach is that jitter, also known as 360° repeatability, can be induced on the output signal. The sample-and- hold process, used by the demodulator to store and recover the signal, can slightly degrade the signal- to-noise ratio. This is because the process generates replicas of the noise spectrum at the baseband, causing a decrease in jitter performance. However, the improve- ment in switchpoint performance, resulting from the reduction of the effects of thermal and mechanical stress, outweighs the degradation in the signal-to-noise ratio. This technique produces devices that have an extremely stable quiescent Hall element output volt- age, are immune to thermal stress, and have precise recoverability after temperature cycling. This tech- nique is made possible through the use of a BiCMOS process, which allows the use of low-offset and low- noise amplifiers in combination with high-density logic integration and sample-and-hold circuits. This process is illustrated in the following diagram. Chopper stabilization circuit (dynamic quadrature offset cancellation) Amp Regulator Low- Pass Filter |
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Similar Description - A3425_06 |
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