Bio-Impedance Transducer Circuit With Current-Mode Noise Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing bio-impedance measurement devices struggle with noise interference from external electrical and magnetic sources, particularly common mode noise, which affects the accuracy of impedance measurements.
Innovation Solution
A bio-impedance transducer system that converts voltage signals to current signals using a high common mode rejection input stage and a continuous time sigma delta analog-to-digital converter (ADC), eliminating the need for an anti-aliasing filter and enhancing noise rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional voltage measurement methods are used for bio-impedance measurement, then the device structure is simple, but noise interference from external electrical and magnetic sources significantly affects measurement accuracy
Solution Approach 1:
The patent replaces traditional voltage measurement methods with current measurement methods. By measuring the current through the body instead of voltage, the system achieves immunity to common-mode noise from external electrical and magnetic sources, as current measurements are inherently reference-free and not affected by ground potential differences or electromagnetic interference.
Solution Approach 2:
The patent changes the measurement parameter from voltage to current. The bio-impedance measurement system measures current directly through the body rather than measuring voltage across electrodes, fundamentally changing the measurement approach to eliminate susceptibility to external noise while maintaining the ability to calculate impedance.
2Measurement precision
If high precision amplification and conversion stages are added to reduce noise, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent performs preliminary conversion of the bio-impedance signal from voltage to current at the input stage, before subsequent processing. By converting to current early in the signal chain, the system establishes a noise-immune signal format that can be processed through standard amplification and ADC stages without requiring special noise-rejection circuitry, thus achieving high precision with moderate complexity.
Solution Approach 2:
The patent introduces a current-mode intermediary stage that converts the voltage signal from the electrodes into a current signal. This intermediary current-mode processing stage acts as a mediator between the input electrodes and the output ADC, providing noise immunity while enabling standard signal processing techniques to be used in the subsequent stages.
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 system achieves precise and efficient bio-impedance measurements with reduced noise interference, suitable for wearable health monitoring devices and IoT applications.
Implementation Method 1
a resistance across the two electrodes to determine an alternating current of the bio-impedance signal
Implementation Method 2
a down converter coupled to the gain stage to convert the amplified alternating current to a direct current bio-impedance signal
Data Source
AI summary
A method and apparatus are described for bio-impedance measurement using voltage to current conversion. In one example, a bio-impedance transducer includes an input stage to receive a bio-impedance signal having an oscillating voltage from two electrodes, the electrodes being coupled to a body, a resistance across the two electrodes to determine an alternating current of the bio-impedance signal, a gain stage coupled to the resistance to amplify the alternating current, a down converter coupled to the gain stage to convert the amplified alternating current to a direct current bio-impedance signal, and an analog-to-digital converter coupled to the down converter to convert the direct current bio-impedance signal to a digital bio-impedance signal.