Biopotential Acquisition Circuit for Electrode Mismatch Compensation
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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, amplifier, feedback circuit, and electrode mismatch compensation circuit to enhance differential input impedance, reduce common mode interference, and adjust output signals based on power line frequency components to mitigate electrode mismatch effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If smaller dry electrodes are used in portable medical devices, then device portability and user comfort are improved, but electrode impedance deteriorates and power line common mode interference increases
Solution Approach 1:
The patent changes the electrical parameters of the input stage by using an operational amplifier with high input impedance configuration. This allows the use of smaller electrodes while maintaining good signal quality by preventing the electrode impedance from degrading the overall system performance. The parameter change occurs in the electrical characteristics of the amplification stage rather than in the electrode physical dimensions.
Solution Approach 2:
The operational amplifier acts as an intermediary between the electrodes and the signal processing circuitry. It mediates the impedance mismatch between small electrodes and the subsequent circuit stages, allowing small electrodes to function effectively without directly coupling their high impedance to the rest of the system.
2Reliability
If bias resistors with large resistance are used to improve signal quality, then signal quality improves, but common mode voltage swing increases causing more power line interference
Solution Approach 1:
The operational amplifier serves as an intermediary that eliminates the need for large bias resistors. By providing a low-impedance input stage through the op-amp, the circuit can achieve good signal quality without relying on large resistance values that would otherwise be required, thereby avoiding the associated common mode voltage swing and power line interference.
Solution Approach 2:
The patent replaces the passive resistor-based biasing mechanism with an active operational amplifier-based input stage. This substitution transitions from a passive electrical component (resistor) to an active component (op-amp), enabling better control over impedance and common mode rejection without the trade-offs inherent in passive resistor networks.
3Device complexity
If the RLD electrode is removed to simplify the two-electrode configuration, then device simplicity is improved, but power line common mode interference becomes serious
Solution Approach 1:
The operational amplifier acts as an intermediary that provides common mode rejection without requiring a third RLD electrode. It mediates between the two-electrode simplicity and the need for interference rejection by actively rejecting common mode signals at the input stage through its differential amplification capability.
Solution Approach 2:
The operational amplifier utilizes feedback mechanisms to actively reject common mode interference. By monitoring the common mode voltage at its inputs and adjusting its output accordingly, the op-amp provides active cancellation of power line interference without requiring additional electrodes or complex passive filtering networks.
Data Source
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.