ECG Electrode Bias Control to Prevent Drive Circuit Saturation
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Solution Overview
Problem
Modern low-voltage ECG systems face drive circuit saturation due to typical ECG electrode impedances, which hinders miniaturization and market implementation, as traditional solutions like high-performance hardware preamplifiers are not desirable due to their large size and higher voltage requirements.
Innovation Solution
The solution involves a method where the charge on each electrode is balanced by varying the bias current via current sources, and the use of pulsed direct current to avoid DC build-up in the right leg drive circuit, allowing for effective removal of unwanted DC signal content on an electrode-by-electrode basis, thereby preventing saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-performance hardware preamplifier circuit is added to the front end of the ASIC at a higher voltage, then drive circuit saturation is prevented, but device size increases and voltage power infrastructure requirements increase
Solution Approach 1:
The patent changes the electrical parameters of the existing low-voltage ASIC by dynamically adjusting bias currents to different electrodes based on measured voltage differentials. This allows the low-voltage circuit to achieve the saturation prevention function previously requiring high-voltage preamplifiers, without increasing device size or voltage infrastructure
Solution Approach 2:
The patent creates a virtual high-voltage reference signal through software control and signal processing within the low-voltage ASIC. By copying and processing the differential voltage measurements through digital signal processing, the system achieves high-voltage-like performance in a low-voltage architecture, avoiding the need for physical high-voltage preamplifier hardware
2Device complexity
If low-voltage ASICs are used to enable miniaturization, then device size is reduced, but drive circuit saturation occurs due to typical ECG electrode impedances
Solution Approach 1:
The patent makes the low-voltage ASIC dynamically adaptive by continuously measuring voltage differentials across electrodes and adjusting bias currents in real-time. This dynamic adjustment allows the fixed low-voltage architecture to adapt to varying electrode impedances, preventing saturation without requiring high-voltage hardware
Solution Approach 2:
The patent implements a feedback control loop where the ASIC measures voltage differentials at the electrodes and uses this information to adjust bias currents through current sources. This closed-loop feedback enables the low-voltage system to maintain optimal operation across varying impedance conditions, preventing drive circuit saturation while preserving miniaturization benefits
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
This approach maximizes the removal of unwanted DC signal content and enables the miniaturization of ECG systems by preventing drive circuit saturation, ensuring accurate ECG measurements and improved common mode rejection.
Implementation Method 1
varying the amount of bias current flowing into each electrode via the current source sense signal
Implementation Method 2
determining, based on the measured parameters, an amount of current leakage in the ECG system due to a contact state of a first electrode
Data Source
AI summary
An Electrocardiography (ECG) system configured to produce an ECG output signal of a patient includes a plurality of electrodes, a monitoring circuit, a drive circuit, a lead circuit, and a control module. The electrodes form a plurality of leads. The monitoring circuit is configured to monitor a voltage differential on the leads and produce the ECG output signal. The drive circuit is configured to deliver a current to the electrodes based on a measured voltage at the electrodes. The lead fault detection system comprises one or more current sources configured to produce a current to deliver to the electrodes. The control module is configured to vary the current produced by the current sources based on a measured parameter at one or more of the electrodes.