Hall Sensor Offset Cancellation Using Switched Differential Amplification
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Solution Overview
Problem
Magnetic sensor devices face inaccuracies in detecting magnetic field intensity due to offset voltages and noise from components like Hall elements, amplifiers, and comparators, which cannot be effectively removed by existing technologies.
Innovation Solution
A magnetic sensor device is designed with a switch and capacitor configuration that cancels out offset components, allowing for precise detection of magnetic field intensity by switching between detection states and using a differential amplifier to isolate the signal voltage from offset voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spinning current method is used to cancel element offset voltage, then element offset voltage is reduced, but input offset voltage of comparator remains and causes detection errors
Solution Approach 1:
The patent applies periodic action by switching the current direction through the Hall element in alternating periods. During the first period, current flows in one direction and the output is stored; during the second period, current flows in the opposite direction and the output is stored. By subtracting these two periodic outputs, the periodic offset components (including element offset voltage and input offset voltage) cancel each other out, while the magnetic field signal is preserved. This periodic switching and subtraction method effectively removes both element offset voltage and comparator input offset voltage.
2Power
If minute output voltage from Hall element is amplified, then signal strength increases, but noise and offset voltages are also amplified
Solution Approach 1:
The patent converts the harmful effect of offset voltages and noise into a beneficial cancellation mechanism. By measuring the output during two opposite current directions and subtracting them, the offset voltages (which are common to both measurements) cancel out, while the magnetic field signal (which reverses polarity with current direction) is doubled. The noise, being random, also tends to cancel out through the subtraction process. This transforms the amplification of harmful factors into an opportunity for their elimination.
Solution Approach 2:
The patent uses a feedback mechanism where the output from the first period is stored and then subtracted from the output of the second period. This feedback loop allows the system to compare and cancel offset components while preserving the magnetic field signal. The subtraction operation effectively feeds back the offset information to eliminate it from the final output.
3Device complexity
If simple amplifier circuit is used, then device complexity is reduced, but offset voltage cancellation is insufficient
Solution Approach 1:
The patent segments the detection process into two distinct periods: the first period for measuring output with current in one direction, and the second period for measuring output with current in the opposite direction. This temporal segmentation allows the system to separate the magnetic field signal from the offset voltage components. By processing these two segmented measurements through subtraction, effective offset cancellation is achieved without requiring complex circuitry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables accurate and precise detection of magnetic field intensity by removing offset components, resulting in a highly reliable magnetic sensor device with improved accuracy.
Implementation Method 1
a magnetoelectric conversion element (such as Hall element) outputs a voltage corresponding to (typically, substantially proportional to) magnetic field intensity
Data Source
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AI summary
Provided is a sensor device capable of removing the influence of each offset voltage of a sensor element, a differential amplifier, and an amplifier of the sensor device, to thereby detect a physical quantity with high precision. The sensor device includes: a switch circuit, which is connected to a first terminal pair and a second terminal pair of the sensor element, for controlling switching of the terminal pairs and outputting detection voltages; a differential amplifier, which includes a first input terminal and a second input terminal connected to a first output terminal and a second output terminal of the switch circuit, respectively, for outputting a result obtained by amplifying a difference of the detection voltages; an amplifier including at least two differential input pairs, one of which inputs the differential signal output from the differential amplifier, and at least one of which inputs a reference signal corresponding to a physical quantity to be detected; and a detection voltage setting circuit for outputting the reference signal to the amplifier.