Magnetic Sensor Offset Cancellation via Differential Amplification
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Solution Overview
Problem
Existing magnetism detecting devices face challenges in achieving high gain while minimizing the influence of offset voltage, leading to complex circuit configurations and reduced accuracy in detecting weak magnetic signals.
Innovation Solution
A magnetism detecting device incorporating a magnetic sensor with an alternating current amplifier circuit, an integrating circuit, and a differential amplifier circuit, which subjects the output signals to alternating current amplification, integration, and differential amplification respectively, effectively canceling out offset voltages and enhancing detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistive voltage divider circuit and amplifier circuit are used for magnetic field detection, then the device can amplify the detection signal, but the offset voltage of the amplifier circuit affects the detection accuracy
Solution Approach 1:
The patent extracts and separates the offset voltage component from the magnetic detection signal through a dedicated offset detection circuit. The offset voltage is detected independently and then subtracted from the main detection signal, removing the harmful offset interference while preserving the actual magnetic field information.
Solution Approach 2:
The patent changes the operating parameters of the amplifier circuit by applying different DC voltage levels to the non-inverting input terminal during offset detection versus normal operation. This parameter change enables the circuit to distinguish between offset voltage and actual magnetic signals, allowing for selective cancellation of the offset component.
2Measurement precision
If multiple stages of amplifier circuits are used to amplify weak magnetic signals, then the gain is increased, but the circuit configuration becomes complex
Solution Approach 1:
The patent combines multiple functions into a single integrated circuit architecture. The offset detection circuit shares operational amplifiers and other components with the main signal processing path, and the high-pass filter is integrated into the same circuit block, reducing overall complexity while maintaining the ability to handle weak signals effectively.
Solution Approach 2:
The patent performs offset voltage detection and cancellation before the main signal amplification process. By removing the offset component in advance, subsequent amplification stages can operate more efficiently with fewer stages needed, as the signal-to-noise ratio is improved before amplification occurs.
3Measurement precision
If the number of amplifier circuit stages is increased to achieve high gain, then weak magnetic signals can be detected, but the offset voltage influence is amplified as well
Solution Approach 1:
The patent extracts the offset voltage component through a separate detection path that measures the amplifier's offset voltage under known conditions (zero magnetic field). This extracted offset information is then used to correct the main detection signal, preventing the amplification of offset errors while maintaining signal amplification.
Solution Approach 2:
The patent implements a feedback mechanism where the detected offset voltage is continuously monitored and subtracted from the main detection signal. This feedback loop ensures that offset voltage effects are dynamically compensated, allowing for high gain amplification without proportionally amplifying the offset error.
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 allows for accurate detection of weak magnetic field changes without offset voltage interference, improving the identification of magnetic patterns on banknotes with higher precision.
Implementation Method 1
a magnetic sensor provided with a resistive voltage divider circuit including a magnetoresistive element
Data Source
Figure 1
Figure 2(A)~2(B)
Figure 3(A)~3(C)
AI summary
A magnetism detecting device that can achieve a high gain and can also detect magnetism without being affected by an offset voltage, and a banknote identifying apparatus that includes such a magnetism detecting device are configured. A magnetism detecting device (101) includes a magnetic sensor (1) that is provided with a resistive voltage divider circuit including a magnetoresistive element (Rl), an alternating current amplifier circuit (20) that subjects an output signal of the magnetic sensor (1) to alternating current amplification, an integrating circuit (30) that integrates an output signal of the alternating current amplifier circuit (20), and a differential amplifier circuit (40) that subjects the output signal of the alternating current amplifier circuit (20) and an output signal of the integrating circuit (30) to differential amplification.