EMG Signal Circuit Layout for Offset-Centered Rectification
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Solution Overview
Problem
Current electromyography (EMG) devices face challenges in effectively processing action potential voltages to provide reliable and versatile EMG signals for therapeutic, rehabilitation, and entertainment applications, often lacking efficient signal processing and output configurations.
Innovation Solution
The EMG device incorporates a main circuit board with snap connectors and a sibling board for modular configuration, featuring a difference circuit, bandpass filter, rectification circuit, and offset removal circuit to process EMG signals, centering them about a non-zero voltage and providing filtered, rectified, and envelope-based output signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If EMG signals are processed using conventional circuits without voltage centering, then the circuit design is simpler, but waveform loss occurs during rectification and resolution is reduced
Solution Approach 1:
The circuit performs preliminary voltage centering by adding an offset voltage to shift the EMG signal from ground-referenced to mid-supply voltage before rectification occurs. This preliminary action prevents waveform loss during subsequent rectification and maximizes the utilization of the analog input range, thereby improving measurement precision without requiring complex post-processing circuits.
Solution Approach 2:
An intermediary offset voltage source is introduced as a mediator between the raw EMG signal and the rectification stage. This intermediary component (typically a voltage reference or bias generator) provides the necessary voltage shift, allowing the signal to be properly centered about mid-supply voltage, which enables effective rectification and improves resolution.
2Reliability
If EMG signals are rectified without prior voltage offset removal, then the processing is more straightforward, but waveform loss occurs and measurement accuracy deteriorates
Solution Approach 1:
The circuit removes voltage offsets as a preliminary action before rectification by using differential amplification or offset cancellation techniques. This ensures that the rectification process operates on a properly centered signal, preventing waveform loss and maintaining measurement accuracy throughout the signal processing chain.
Solution Approach 2:
The circuit employs feedback mechanisms to detect and compensate for voltage offsets in the EMG signal. By continuously monitoring the signal level and adjusting the offset compensation accordingly, the system maintains accurate signal representation through rectification, thereby improving reliability without requiring overly complex processing circuits.
3Measurement precision
If the circuit utilizes the full analog input range for EMG signals, then the resolution is maximized, but the circuit requires precise voltage centering and offset control
Solution Approach 1:
The circuit establishes equipotential conditions by centering the EMG signal about mid-supply voltage, creating a symmetric voltage range that maximizes the utilization of the available analog input range. This is achieved through careful biasing and offset compensation that ensures the signal swings equally above and below the mid-supply reference, thereby optimizing resolution without requiring excessively complex voltage control circuits.
Data Source
AI summary
An electromyography (EMG) device according to an aspect of the present disclosure includes a main circuit board having opposing first and second faces. A plurality of first connectors of a first type are provided on the first face, and a plurality of input contacts are provided on the second face. An EMG circuit is provided on the main circuit board. The EMG circuit is configured to utilize the input contacts as inputs to obtain an EMG input signal, and process the EMG input signal to provide an EMG output signal that is based on, but different from, the EMG input signal. For each of the input contacts, there is no conductive path directly between the input contact and any of the first connectors.