Medical Amplifier Isolation With Capacitive Noise Shunting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Medical amplifiers are susceptible to radiated noise due to the isolation of patient ground from earth ground, leading to common-mode voltage generation and leakage currents via parasitic capacitance, which cannot be effectively rejected, compromising signal quality and safety.
Innovation Solution
A capacitive coupling is introduced across the patient isolation stage between patient ground and a functional ground, providing a lower impedance path for noise currents, thereby reducing leakage currents and improving common-mode rejection ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If patient ground is isolated from earth ground, then patient safety is improved, but susceptibility to radiated noise and leakage current increases
Solution Approach 1:
A capacitive coupling circuit is introduced as an intermediary element between the patient ground and earth ground. This capacitor provides a controlled impedance path that mediates between the need for isolation (safety) and the need for noise rejection, allowing the system to benefit from both isolation and reduced susceptibility to radiated noise.
Solution Approach 2:
The patent changes the electrical parameter (impedance) between patient ground and earth ground by introducing a capacitor with specific capacitance value. This parameter change creates a frequency-dependent impedance that blocks high-frequency noise while allowing low-frequency signals to pass, thereby reducing susceptibility to radiated noise while maintaining isolation for safety.
2Reliability
If patient ground is isolated from earth ground, then isolation is improved, but common-mode voltage generation increases
Solution Approach 1:
The capacitive coupling acts as an intermediary that provides a reference path for common-mode voltages. By connecting the isolated patient ground to earth ground through a capacitor, the system maintains isolation while providing a controlled path for common-mode currents, thereby reducing the magnitude of generated common-mode voltages.
3Reliability
If patient ground is isolated from earth ground, then electrical isolation is improved, but differential voltage that cannot be rejected increases
Solution Approach 1:
The patent modifies the impedance parameter of the connection between patient ground and earth ground by using a capacitor instead of a direct connection. This creates a frequency-selective impedance that allows the system to maintain electrical isolation while reducing the differential voltage errors that degrade measurement precision.
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 capacitive coupling significantly reduces leakage current and differential voltage, enhancing the signal-to-noise ratio and maintaining patient safety while meeting isolation and leakage current standards.
Implementation Method 1
A capacitive coupling is introduced across the patient isolation stage between patient ground and a functional ground, providing a lower impedance path for noise currents
Data Source
AI summary
This disclosure provides isolation for a medical amplifier by providing a low impedance path for noise across an isolation barrier. The low impedance path can include a capacitive coupling between a patient ground, which is isolated from control circuitry, and a functional ground of an isolation system that is isolated from earth ground. The low impedance path can draw noise current from an input of an amplifier of patient circuitry.