Magnetic Field Sensor Current-Mode Offset Averaging
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Solution Overview
Problem
Magnetic field sensors, such as Hall effect and magnetoresistance sensors, suffer from offset voltages due to resistance gradients and geometrical asymmetries, which vary with mechanical pressure and temperature, leading to signal imbalances and susceptibility to saturation.
Innovation Solution
Implementing a current mode signal path with a modulation circuit, amplifier, sample and hold circuit, and switch point circuit to modulate and average magnetic field signals, effectively separating and reducing offset components, thereby improving handling and reducing signal path saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chopper stabilization techniques are used to cancel Hall offset voltage, then offset handling is improved, but device complexity and die area increase
Solution Approach 1:
The patent extracts the offset cancellation function from the traditional chopper stabilization circuitry and implements it through a current mode signal path with separate sampling of offset components. The offset cancellation is achieved by sampling the offset voltage at specific phases and subtracting it from the total signal, rather than using complex chopper modulation circuits.
Solution Approach 2:
The patent segments the signal processing into distinct phases: offset sampling phase and signal measurement phase. By using multiple sample and hold circuits that operate at different phases, the offset component is separated and cancelled independently from the magnetic field signal, reducing the need for complex continuous chopper circuits.
2Measurement precision
If traditional voltage mode signal conditioning is used, then offset cancellation is achieved, but susceptibility to signal path saturation increases
Solution Approach 1:
The patent changes the signal domain from voltage mode to current mode for signal conditioning. Current mode operation provides higher input impedance and avoids the saturation issues inherent in voltage mode amplifiers. The current signals are processed through transconductance amplifiers that maintain linearity over a wider dynamic range.
3Measurement precision
If switched Hall plate modulation is used to discriminate offset from magnetic signal, then offset discrimination is improved, but device complexity increases
Solution Approach 1:
The patent employs periodic switching of the Hall plate connections to modulate the magnetic field signal while keeping the offset signal invariant. By alternating the supply voltage connections to the Hall plate contacts in quadrature phases, the magnetic signal is modulated at the switching frequency while the offset remains at DC, enabling easy separation through filtering and sampling.
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
The solution achieves smaller die area and improved offset handling with reduced susceptibility to signal path saturation, enhancing the performance of magnetic field sensors.
Implementation Method 1
Magnetic field sensors-such as Hall effect, Giant Magnetoresistance (GMR), and Tunnel Magnetoresistance (TMR) sensors-are used in a wide variety of applications
Data Source
Figure 1~1A
Figure 2
Figure 3A
AI summary
According to some embodiments, a sensor includes: one or more sensing elements configured to generate a magnetic field signal having a magnetic field component that varies in response to a magnetic field and an offset component contributed by the one or more sensing elements; a modulation circuit configured to modulate the magnetic field component of the magnetic field signal at a modulation frequency; an amplifier configured to receive the modulated signal and provide an amplified modulated signal having a current responsive to at least the magnetic field and the offset contributed by the one or more sensing elements; and a sample and hold circuit configured to receive the amplified modulated signal and provide a conditioned signal having a current that varies in response to the magnetic field signal and having substantially zero offset contribution from the one or more sensing elements and from the amplifier.