Biopotential Acquisition Circuit for Two-Electrode Noise Rejection
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Solution Overview
Problem
Conventional portable medical devices with smaller dry electrodes face issues of worse electrode impedance and increased power line common mode interference due to the removal of the right-leg-drive electrode, which compromises signal quality and introduces differential mode voltage from electrode mismatch.
Innovation Solution
A biopotential acquisition system circuit incorporating an active current source and amplifier with a feedback circuit to provide high differential input impedance and low common mode input impedance, along with an electrode mismatch compensation circuit to adjust output signals and reduce power line common mode interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two bias resistors with large resistance are used to provide bias voltages to improve signal quality, then signal quality of biopotential signals is improved, but common mode voltage swing increases causing more serious power line common mode interference
Solution Approach 1:
The patent changes the electrical parameters of the input terminals by configuring them as virtual ground nodes with controlled impedance characteristics. This allows the circuit to maintain high common mode rejection ratio while using smaller bias resistors, thereby improving signal quality without exacerbating power line interference.
Solution Approach 2:
The differential amplifier configuration provides inherent feedback mechanisms that reject common mode signals. The circuit automatically balances the voltages at the two input terminals, creating a feedback loop that suppresses common mode interference while preserving differential signal quality.
2Ease of operation
If smaller dry electrodes are used in portable medical devices, then device portability and user comfort are improved, but electrode impedance worsens affecting signal quality
Solution Approach 1:
The patent changes the input impedance parameters of the amplifier circuit to match the high-impedance characteristics of small dry electrodes. By configuring the input terminals as virtual grounds with high impedance, the circuit maximizes signal acquisition from small electrodes without requiring large electrode sizes, thus maintaining both portability and signal quality.
3Device complexity
If the right-leg-drive electrode is removed to simplify the two-electrode portable device, then device complexity is reduced, but power line common mode interference becomes serious
Solution Approach 1:
The patent extracts and eliminates the need for the third RLD electrode by reconfiguring the two-electrode system with virtual ground input terminals. The differential amplifier configuration inherently rejects common mode interference without requiring the traditional RLD electrode, thus simplifying the device while maintaining interference rejection capability.
Solution Approach 2:
The patent replaces the mechanical/electrical RLD electrode system with an electronic solution based on virtual ground configuration and differential amplification. This substitution eliminates the need for physical electrode placement on the right leg while achieving equivalent or superior common mode rejection through electronic circuit design.
Data Source
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AI summary
The present invention provides a circuit applied to a biopotential acquisition system, wherein the circuit includes an active current source and an amplifier. In the operations of the circuit, the active current source is configured to provide a current to two input terminals of the circuit, wherein the two input terminals of the circuit are coupled to two input electrodes of the biopotential acquisition system; and the amplifier is configured to receive input signals from the two input terminals to generate an output signal.