Biological Signal Detection Circuit With AC-Coupled Differential Amplification
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing detection circuits for biological signals like electrocardiograms face challenges in accurately amplifying weak signals due to high amplification factors leading to signal waveform clamping and distortion, caused by differences in direct-current voltage components between detection signals.
Innovation Solution
A detection circuit design incorporating high impedance circuits connected to reference measurement potentials, coupling capacitors to remove direct-current voltage components, and operational amplifiers with automatic gain control to optimize signal amplification and noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the amplification factor of the differential amplifier is set high to amplify weak detection signals, then the signal amplitude increases, but signal waveform clamping or distortion occurs due to differences in direct-current voltage components
Solution Approach 1:
The patent divides the amplification function into two separate amplification units (first amplification unit and second amplification unit) that operate independently on each detection signal before differential processing. This segmentation allows each unit to amplify its respective signal without the direct-current voltage difference problem that occurs in a single differential amplifier, thereby maintaining signal waveform integrity while achieving the required amplification for weak detection signals
Solution Approach 2:
The patent introduces coupling capacitors as intermediary elements between the amplification units and the differential circuit. These coupling capacitors block direct-current voltage components while allowing alternating current detection signals to pass through, thereby eliminating the direct-current voltage difference that causes waveform clamping and distortion, while still enabling effective amplification of the weak detection signals
2Reliability
If coupling capacitors are provided between detection electrodes and differential amplifier to remove direct-current voltage components, then direct-current voltage differences are reduced, but signal-to-noise ratio deteriorates due to characteristic variations of electronic components
Solution Approach 1:
The patent segments the signal processing into two stages: first, independent amplification of each detection signal through separate amplification units that maintain high input impedance; second, differential processing after coupling capacitors remove direct-current components. This segmentation allows the system to benefit from both high impedance amplification (maintaining signal-to-noise ratio) and direct-current removal (maintaining waveform integrity)
Solution Approach 2:
The patent employs automatic gain control that dynamically adjusts the amplification factors of the first and second amplification units based on the detected signal levels. This dynamic adjustment optimizes the signal-to-noise ratio by ensuring that weak signals are amplified sufficiently while preventing saturation from stronger signals, thereby maintaining measurement precision throughout varying signal conditions
3Measurement precision
If high impedance circuits are connected between detection electrodes and amplification units to prevent signal leakage, then detection of weak signals is improved, but direct-current voltage components increase
Solution Approach 1:
The patent segments the impedance function by providing high impedance circuits only at the input stage (between detection electrodes and amplification units) while maintaining lower impedance in subsequent stages. This segmented impedance design allows high input impedance to prevent signal leakage and enable weak signal detection, while the coupling capacitors and differential processing in later stages remove the resulting direct-current voltage components
Solution Approach 2:
The coupling capacitors serve as intermediary elements that isolate the high impedance input stage from the subsequent amplification and differential processing stages. They block the direct-current voltage components generated by the high impedance circuits while allowing the amplified alternating current detection signals to pass through to the differential circuit, thereby resolving the conflict between weak signal detection and direct-current voltage stability
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 configuration improves the signal-to-noise ratio, prevents signal waveform clamping, and enhances common-mode-noise cancellation, allowing for stable and accurate detection of weak biological signals.
Implementation Method 1
an output terminal of the first amplification unit and a first input terminal of the differential circuit are connected to each other through a first coupling capacitor, and an output terminal of the second amplification unit and a second input terminal of the differential circuit are connected to each other through a second coupling capacitor
Implementation Method 2
an input terminal of the first amplification unit is connected to a first detection electrode, and connected on one end side of a first high impedance circuit whose other end side is connected to a reference measurement electric potential
Data Source
AI summary
An amplifier circuit includes first and second amplification units. A first detection electrode and a high impedance circuit are connected to the input terminal of the first amplification unit. A second detection electrode and a high impedance circuit are connected to the input terminal of the second amplification unit. The output terminals of the first and second amplification units output first and second output signals, and are connected to the input terminals of a differential amplifier circuit through coupling capacitors, respectively. The differential amplifier circuit operates a difference between the first and second output signals in a state where a direct-current component is omitted.