TMR Sensor Readout Circuit Using Common-Mode Feedback
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Solution Overview
Problem
Current biomagnetic signal detection methods face challenges with low spatial resolution, high noise levels, and the need for invasive electrodes, which can lead to discomfort and infection, while existing magnetic sensors are bulky, costly, and require controlled environments.
Innovation Solution
A readout integrated circuit (IC) architecture for tunnelling magnetoresistive (TMR) sensors using a three-operational amplifier configuration with chopper stabilization and common-mode feedback, integrated with a magnetic sensor array, enabling high spatial and temporal resolution biomagnetic signal detection without invasive electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional bioelectricity recording methods are used, then temporal resolution is achieved, but spatial resolution remains poor and invasive electrodes cause discomfort and infection risk
Solution Approach 1:
The patent replaces the mechanical contact-based bioelectricity recording system with a magnetic field-based detection system. TMR sensors detect biomagnetic fields generated by neural activity without requiring physical contact or penetration of the skin, thereby eliminating infection risk while maintaining high temporal resolution and achieving superior spatial resolution through miniaturized sensor arrays that can be positioned close to the head.
Solution Approach 2:
The patent changes the detection parameter from electrical potential (requiring contact) to magnetic field strength (detectable without contact). This parameter change enables non-invasive measurement while preserving temporal fidelity. The TMR sensors operate at room temperature with high sensitivity to detect the weak biomagnetic fields, resolving the contradiction between non-invasiveness and measurement capability.
2Measurement precision
If SQUIDs or OPMs are used for magnetic field detection, then sensitivity is improved, but device size increases and controlled environment requirements are imposed
Solution Approach 1:
The patent changes the operating conditions of magnetic sensors by using TMR technology that operates at room temperature instead of requiring cryogenic temperatures (SQUIDs) or complex optical pumping systems (OPMs). This parameter change in operating temperature enables miniaturization and eliminates the need for large magnetically shielded rooms, while maintaining pico-Tesla level sensitivity through the high tunneling magnetoresistance effect in the TMR junctions.
Solution Approach 2:
The patent extracts the magnetic sensing functionality from the bulky, environment-dependent SQUID and OPM systems and integrates it into compact TMR sensor arrays that can be incorporated into portable devices. This extraction removes the requirement for large magnetically shielded environments and complex support infrastructure, enabling wearable biomagnetic measurement systems.
3Volume of moving object
If GMR sensors are used, then device miniaturization is achieved, but sensitivity remains in the nano-Tesla range requiring averaging
Solution Approach 1:
The patent uses composite material structures in the TMR sensor design, combining ferromagnetic layers with high anisotropy, non-magnetic spacer layers, and tunnel barrier materials to achieve both miniaturization and enhanced sensitivity. The composite structure of multiple thin films with specific magnetic and electrical properties enables the TMR effect to produce giant resistance changes in response to weak magnetic fields, achieving pico-Tesla sensitivity in miniaturized sensors without requiring sensor arrays or signal averaging.
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 low input-referred noise of nV/√Hz, allowing for accurate and comfortable detection of biomagnetic signals with improved spatial resolution and reduced power consumption, suitable for wearable biosensors.
Implementation Method 1
tunnelling magnetoresistive (TMR) sensors that are highly miniaturized and can be operated at room temperature using a sensor array
Implementation Method 2
The differential amplifier includes a common-mode feedback (CMFB) circuit configured to eliminate a common-mode current component from the differential input signals
Implementation Method 3
The architecture may use a three-operational amplifier configuration with chopper stabilization
Data Source
AI summary
A readout integrated circuit (IC) architecture for a tunnelling magnetoresistive (TMR) sensor which uses common mode feedback to achieve a performance level suitable for accurate detection of biomagnetic signals. The architecture uses a three-operational amplifier configuration with chopper stabilization. The architecture may form part of a fully integrated biomagnetic sensor electronics package that includes an array of TMR sensors together with modules for signal amplification and conditioning, data conversion and communication.