ECG LPF Capacitor Calibration for Common-Mode Rejection
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Solution Overview
Problem
Existing ECG systems face challenges in accurately rejecting common mode signals due to component mismatch in Low Pass Filter (LPF) circuits, leading to degraded Common Mode Rejection Ratio (CMRR), which is costly to improve with tighter component tolerances and requires additional hardware and processing complexity.
Innovation Solution
An ECG system with a calibration mode that adjusts adjustable capacitors to match the phase of input signals, correcting for component mismatch in the analog domain, thereby improving CMRR without the need for extra hardware or higher processing speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tighter component tolerances are used in LPF circuits to improve CMRR, then measurement precision is improved, but manufacturing precision requirements increase and device complexity increases
Solution Approach 1:
The patent applies preliminary action by performing phase calibration before actual ECG signal processing. The system pre-adjusts the phase of input signals using adjustable capacitors during a calibration phase, so that when normal operation begins, the signals are already properly aligned. This preliminary phase matching eliminates the need for tight component tolerances during manufacturing, as the calibration process compensates for component variations.
Solution Approach 2:
The patent changes the capacitance values of adjustable capacitors in the LPF circuits to compensate for phase mismatches. By dynamically adjusting the capacitance parameter rather than relying on fixed tight-tolerance components, the system achieves improved CMRR. The calibration circuitry modifies these capacitance values based on measured phase differences, allowing the system to adapt to component variations without requiring stringent manufacturing precision.
2Measurement precision
If additional hardware is added to correct component mismatch and improve CMRR, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent makes existing hardware components multi-functional. The adjustable capacitors and phase detection circuitry serve dual purposes: they are used during calibration to match signal phases, and then remain in place during normal ECG operation to maintain the corrected phase relationships. This eliminates the need for separate correction hardware, as the same components perform both calibration and operational functions.
Solution Approach 2:
The system performs self-calibration using its own existing resources. The calibration circuitry uses the adjustable capacitors and phase detection capabilities already present in the ECG system to automatically detect and correct phase mismatches. This self-service approach eliminates the need for external calibration equipment or additional complex correction hardware, as the system calibrates itself using its own components.
3Measurement precision
If higher processing speeds are used to compensate for component mismatch, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent replaces high-speed digital signal processing with analog phase adjustment in the LPF circuits. Instead of using complex digital algorithms that require high processing speeds to correct component mismatches, the system uses adjustable capacitors to directly adjust the phase of analog signals. This analog approach achieves the same correction effect with minimal processing, thereby reducing power consumption.
4Device complexity
If calibration process is simplified, then device complexity is reduced, but measurement precision may deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where the calibration circuitry continuously monitors the phase relationship between differential input signals and automatically adjusts the capacitance values of adjustable capacitors to minimize phase differences. This closed-loop feedback ensures that the simplified calibration process still achieves high measurement precision, as the system automatically optimizes the phase matching rather than relying on complex manual calibration procedures.
Data Source
AI summary
An example apparatus includes: an adjustable capacitor having a first terminal coupled to an input terminal, a second terminal coupled to ground, and a control terminal; demodulation circuitry having an input coupled to the first terminal of the adjustable capacitor; calibration circuitry having an input coupled to an output of the demodulation circuitry and an output coupled to the control terminal of the adjustable capacitor; and driver circuitry having an input coupled to the adjustable capacitor and an output coupled to an output terminal.