Twisted TMR Bridge Layout for Low-Noise Current Sensing
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Solution Overview
Problem
Magnetic sensors with Wheatstone bridge circuits using TMRs face issues of increased chip area and di/dt noise due to induced electromotive forces and common-mode signals from magnetic flux distribution, which degrade signal quality.
Innovation Solution
The design incorporates a twisted Wheatstone bridge circuit with alternating magnetic field detection directions and twisted wiring lines to cancel out induced electromotive forces and suppress di/dt noise, using a magnetic sensor to detect current-induced magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple TMRs are connected in series to constitute each resistor arm, then DC voltage resistance and ESD voltage resistance are improved, but chip area increases and di/dt noise is generated
Solution Approach 1:
The patent transitions from a planar arrangement of TMRs to a three-dimensional stacked configuration. Multiple TMRs are arranged vertically in layers rather than horizontally in series, maintaining the series connection for voltage resistance while reducing the lateral chip area occupied by the same number of elements.
Solution Approach 2:
The patent implements a nested structure where multiple TMR layers are stacked within a compact vertical space. Each TMR layer is nested above the previous one, allowing multiple magneto resistive elements to occupy a smaller footprint area while maintaining their series connection for improved voltage resistance.
2Reliability
If multiple TMRs are connected in series to constitute each resistor arm, then DC voltage resistance and ESD voltage resistance are improved, but di/dt noise is generated due to induced electromotive force
Solution Approach 1:
The patent introduces asymmetric twist angles between adjacent TMR layers. By setting different magnetic field detection directions for each layer (e.g., 0°, 45°, 90°, 135°), the induced electromotive forces from magnetic flux changes in different layers do not add up coherently, thereby suppressing di/dt noise while maintaining voltage resistance benefits.
Solution Approach 2:
The patent converts the harmful effect of magnetic flux-induced electromotive force into a beneficial noise cancellation mechanism. By carefully designing the twist angles between layers, the induced voltages from each layer interfere destructively, transforming what would be noise into a noise-reduction mechanism that preserves the voltage resistance advantage.
3Reliability
If multiple TMRs are connected in series to constitute each resistor arm, then DC voltage resistance and ESD voltage resistance are improved, but common-mode signal is generated due to magnetic field distribution
Solution Approach 1:
The patent uses asymmetric twist angles between TMR layers to differentiate their magnetic field detection directions. This asymmetry causes each layer to respond differently to common-mode magnetic field variations, enabling the differential circuit to reject common-mode signals while preserving the voltage resistance benefits of series-connected TMRs.
Solution Approach 2:
The patent assigns different local properties (magnetic field detection directions) to different TMR layers through varied twist angles. This local differentiation allows each layer to contribute uniquely to the overall signal, improving the differential mode signal quality while maintaining voltage resistance, as each layer's unique orientation provides localized noise rejection capability.
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 effectively reduces di/dt noise and common-mode signals, improving signal quality and accuracy in current detection devices.
Implementation Method 1
a magnetic sensor which has a Wheatstone bridge circuit composed of four resistor arms each of which includes a magneto resistive element
Implementation Method 2
as a result of a chip area increasing, in other words, a closed loop formed by the four resistor arms increasing, and a large number of magnetic fluxes passing through the inside of the closed loop, not only an induced electromotive force is generated, resulting in a di/dt noise
Data Source
AI summary
A magnetic sensor 50 includes: a resistor arm Ra having: a plurality of magneto resistive elements 51a; an electrode piece 52a which connects upper surfaces of two magneto resistive elements 51a; and an electrode piece 53a which connects lower surfaces of two magneto resistive elements 51a, where the plurality of magneto resistive elements 51a are alternately connected in array sequence by the electrode pieces 52a and 53a; and a resistor arm Rb having: a plurality of magneto resistive elements 51b; an electrode piece 52b which connects upper surfaces of two magneto resistive elements 51b; and an electrode piece 53b which connects lower surfaces of two magneto resistive elements 51b, where the plurality of magneto resistive elements 51b are alternately connected in array sequence by the electrode pieces 52b and 53b.