Hybrid Magnetic Field Sensor Using CT-ΣΔ DC Offset Cancellation
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Solution Overview
Problem
Conventional hybrid magnetic field sensors face limitations in accurately measuring fast-switching currents due to low-frequency current sensing architectures, leading to high-frequency magnetic field component measurement inaccuracies, and require large DC decoupling capacitors, off-chip components, and DC servo loops that introduce noise, cost, and bandwidth limitations.
Innovation Solution
Implementing a direct current (DC) component rejection path coupled with a high-frequency magnetic field component path, using either digital- or analog-based solutions, which eliminates the need for DC decoupling capacitors and reduces noise, incorporating a Continuous-Time Sigma-Delta Analog-to-Digital Converter (CT-ΣΔ ADC) and digital or analog integrators to generate a DC component cancellation signal, and optionally utilizing XMR sensors and vertical Hall sensors for enhanced bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional hybrid magnetic field sensors use low-frequency current sensing architectures, then DC and low-frequency magnetic field components can be measured, but high-frequency magnetic field component measurement accuracy deteriorates
Solution Approach 1:
The patent divides the magnetic field sensing into two separate paths: a first path for high-frequency magnetic field components and a second path for DC and low-frequency magnetic field components. Each path uses optimized sensor elements and circuitry tailored to its frequency range, eliminating the compromise of using a single architecture for all frequencies.
Solution Approach 2:
The patent adds a frequency-dimension separation by implementing parallel sensing paths with different architectural characteristics. The high-frequency path uses one type of sensor element while the low-frequency path uses another, allowing simultaneous optimization for both frequency ranges without interference.
2Measurement precision
If DC decoupling capacitors are used in hybrid magnetic field sensors, then DC offset can be blocked, but device complexity and noise increase
Solution Approach 1:
The patent extracts and removes the DC decoupling capacitors from the high-frequency path by implementing a DC servo loop that actively compensates for DC offsets through feedback. This replaces passive component-based DC blocking with an active electronic solution, reducing component count and associated noise.
Solution Approach 2:
The patent implements a DC servo loop that continuously monitors the output for DC offset components and generates compensating signals to cancel them. This feedback mechanism dynamically maintains DC rejection without requiring large decoupling capacitors, thereby reducing device complexity and noise.
3Measurement precision
If off-chip components and DC servo loops are used, then DC component rejection can be achieved, but bandwidth limitations and noise are introduced
Solution Approach 1:
The patent merges the DC rejection functionality directly into the chip by integrating the DC servo loop circuitry with the sensor elements. This eliminates the need for off-chip components and reduces the bandwidth-limiting effects of external connections, while maintaining effective DC component rejection.
Solution Approach 2:
The patent replaces passive mechanical/electrical DC blocking methods (capacitors) with an active electronic feedback system (DC servo loop) that uses operational amplifiers and feedback networks. This substitution enables better DC rejection performance without the bandwidth limitations and noise associated with large decoupling capacitors.
4Measurement precision
If Hall sensor elements are used for DC and low-frequency measurement, then measurement accuracy is improved, but high-frequency response is limited
Solution Approach 1:
The patent segments the sensing function by assigning Hall sensor elements specifically to the DC and low-frequency path where they excel, while using coil-based sensors or other high-frequency optimized elements for the high-frequency path. This segmentation allows each sensor type to operate in its optimal frequency range.
5Measurement precision
If coil-based sensors are used for high-frequency measurement, then noise is reduced, but low-frequency measurement capability is lost
Solution Approach 1:
The patent segments the sensing function by assigning coil-based sensors specifically to the high-frequency path where they provide low noise performance, while using Hall sensor elements for the DC and low-frequency path. This segmentation allows each sensor type to operate in its optimal frequency range without compromise.
Solution Approach 2:
The patent creates a universal hybrid sensor system that can measure across the entire frequency spectrum from DC to high frequencies by combining multiple sensor types in parallel paths. Each sensor type contributes its strengths to the overall system, achieving multi-frequency capability that neither sensor type could achieve alone.
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 enables high-bandwidth, high-accuracy magnetic field measurements with reduced DC offset, eliminating the need for external components and improving sensor accuracy by effectively canceling DC components and reducing quantization noise.
Implementation Method 1
a Continuous-Time Sigma-Delta Analog-to-Digital Converter (CT-ΣΔ ADC) configured to generate digital data based upon the sensor signal
Implementation Method 2
digital integration circuitry configured to perform a digital integration of the digital data to output a digital representation of a DC component cancellation signal
Implementation Method 3
a digital to analog converter (DAC) configured to convert the digital representation of the DC component cancellation signal to an analog form
Implementation Method 4
an amplifier configured to output a voltage signal based upon the current signal
Data Source
AI summary
The described techniques address issues associated with hybrid current or magnetic field sensors used to detect both low- and high-frequency magnetic field components. The hybrid sensor implements a DC component rejection path in the high-frequency magnetic field component path. Both digital and analog implementations are provided, each functioning to generate a DC component cancellation signal to at least partially cancel a DC component of a current signal generated via the high-frequency magnetic field component path. The hybrid sensor provides a high-bandwidth, high-accuracy, and low DC offset hybrid current solution that also eliminates the need for DC decoupling capacitors in the high-frequency path. A modification is also described for implementing a Sigma-Delta (ΣΔ) quantization noise reduction path to reduce the quantization noise and to improve accuracy.