Bioimpedance Signal Measurement With Common-Mode Reset Timing
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Solution Overview
Problem
Existing bioimpedance measuring devices face challenges in accurately and quickly measuring bioimpedance signals due to issues with common mode voltage interference, which affects the accuracy and efficiency of impedance measurement.
Innovation Solution
A signal measuring apparatus that includes a power source, a reset unit to reset the input voltage signal to a common mode voltage, and an amplifier to generate an amplified signal, along with an analog-to-digital converter to convert the signal into a digital form, effectively reducing common mode voltage interference and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If common mode voltage is not reset during measurement, then the circuit operates continuously without interruption, but measurement accuracy deteriorates due to common mode voltage interference
Solution Approach 1:
The patent implements periodic resetting of the input voltage signal to common mode voltage during the carrier frequency period. The reset unit periodically clamps the input voltage to common mode voltage at specific timing points, eliminating cumulative common mode interference while maintaining measurement accuracy. This periodic action resolves the contradiction by introducing controlled interruptions that improve precision without significantly increasing circuit complexity.
2Measurement precision
If reset operation is performed frequently to improve accuracy, then measurement precision improves, but measurement time is reduced due to reset intervals
Solution Approach 1:
The patent performs the reset operation at optimally timed intervals before measurement critical points, preparing the input voltage signal in advance to be at common mode voltage level. This preliminary resetting ensures that when measurement begins, the signal is already in the optimal state, achieving high precision without requiring frequent interruptions during the actual measurement process.
Solution Approach 2:
The reset unit operates periodically at specific phases of the carrier frequency cycle, resetting the input voltage to common mode voltage at predetermined timing points. This periodic timing ensures that measurements are taken during optimal windows when the signal has been freshly reset, balancing accuracy requirements with continuous measurement capability and minimizing time loss.
3Measurement precision
If amplifier gain is increased to improve signal detection, then measurement sensitivity improves, but common mode interference is also amplified
Solution Approach 1:
The patent extracts and removes the common mode voltage component from the input signal before it enters the amplifier. The reset unit acts as a common mode rejection stage that separates and eliminates the harmful common mode voltage, allowing the amplifier to process only the differential signal of interest. This extraction approach enables high amplifier gain for improved sensitivity without amplifying common mode interference.
Solution Approach 2:
The reset unit serves as an intermediary stage between the signal source and the amplifier. It mediates by conditioning the input voltage signal, removing common mode components, and presenting a cleaned signal to the amplifier. This intermediary function allows the amplifier to operate at high gain settings while the reset unit protects against amplifying common mode interference, resolving the contradiction between sensitivity and interference.
Data Source
AI summary
A signal measuring apparatus and method is provided. The signal measuring apparatus inputs a reduced voltage signal to an input end of an amplifier by resetting a voltage signal, which is acquired by applying a known current signal to a target object, using a common mode voltage at least once during one period of a current signal. The signal measuring apparatus acquires a digital signal corresponding to an object impedance change by converting an output of the amplifier.