ASIC Multiplexer Switching with Reference Precharge for ECG Noise
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Solution Overview
Problem
Existing ECG systems face issues with switching noise when multiplexing multiple analog signals, which can distort the bioelectric signals and affect the accuracy of heart monitoring.
Innovation Solution
Incorporating a double pole double throw (DPDT) switch in the multiplexer that first connects to a reference signal and then to the incoming ECG signal, reducing switching noise by minimizing charge injection and allowing for fast settling times, and using a differential amplifier with a buffer to process the signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a multiplexer is used to transfer multiple analog ECG signals through a single A/D converter, then the number of A/D converters is reduced and system complexity is lowered, but switching noise is introduced into the signal path
Solution Approach 1:
The DPDT switch connects to a reference signal before connecting to the incoming ECG signal at each switching event. This preliminary connection to a known reference voltage levels the electrical potential and discharges parasitic capacitances, preventing charge injection noise from contaminating the bioelectric signal.
Solution Approach 2:
A buffer amplifier is introduced between the DPDT switch and the ECG signal path. This intermediary component isolates the switching noise from the signal path while maintaining signal integrity, allowing the multiplexer to function without directly coupling switch noise to the A/D converter input.
2Productivity
If switching speed is increased to reduce settling time, then productivity is improved, but switching noise and signal distortion increase
Solution Approach 1:
By connecting to the reference signal before the ECG signal, the switch completes its transition in a controlled sequence. This preliminary action allows the switch to settle to a known voltage level first, enabling faster switching speeds without compromising signal accuracy during the subsequent ECG signal connection.
Solution Approach 2:
The switch operates with optimized timing parameters where the reference signal connection duration is sufficient to discharge parasitic capacitances but minimized to maintain high switching speed. This parameter optimization allows fast switching while ensuring noise reduction through controlled settling time.
Data Source
AI summary
Medical catheterization is carried out by receiving a plurality of analog bioelectric signals in respective channels and multiplexing the bioelectric signals in respective selection events. The selection events comprise making a first connection with a reference voltage, thereafter breaking the first connection and making a second connection with one of the bioelectric signals. The method is further carried out by outputting the multiplexed bioelectric signals to an analog-to-digital converter.