EEG Cap One-Wire Network High Input Impedance Amplifiers
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Solution Overview
Problem
Current EEG recording systems face challenges with low spatial and temporal resolution, susceptibility to noise, and portability issues due to cumbersome cables and connectors, making it difficult to record high-frequency brain signals non-invasively with adequate sensitivity and accuracy.
Innovation Solution
A novel EEG recording system featuring a one-wire tightly-connected network of Built-in-Electrode Chips EEG cap with narrow-band amplifiers and twisted differential feedback topology, enabling high input impedance and dynamic referencing to enhance signal quality and immunity to artifacts, while allowing for real-time parallel acquisition and computation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If commercial EEG recorders are used, then EEG signals can be recorded, but the input bandwidth is low and high-frequency signals cannot be detected
Solution Approach 1:
The EEG recording system is divided into multiple independent channels, each equipped with its own amplifier and analog-to-digital converter. This segmentation allows each channel to be optimized for wide bandwidth while maintaining overall system coherence, enabling simultaneous recording of multiple frequency bands including high-frequency gamma signals.
Solution Approach 2:
A high-input impedance amplifier stage is introduced as an intermediary between the electrode and the recording system. This amplifier with input impedance greater than 1 GΩ acts as a buffer that prevents loading effects and enables detection of high-frequency signals without requiring wet electrodes or conductive gel.
2Reliability
If wet electrodes are used, then signal quality improves, but portability decreases and repeated gel application is required
Solution Approach 1:
A high-input impedance amplifier stage is introduced as an intermediary between the electrode and the recording system. This amplifier with input impedance greater than 1 GΩ acts as a buffer that prevents loading effects and enables detection of high-frequency signals without requiring wet electrodes or conductive gel.
Solution Approach 2:
The system changes the critical parameter of input impedance from typical values (100 kΩ to 1 MΩ) to ultra-high values (greater than 1 GΩ). This parameter change fundamentally alters the electrode requirements, allowing the use of dry electrodes that are portable and maintenance-free while maintaining signal quality.
3Measurement precision
If high gain amplification is used to detect low-amplitude signals, then sensitivity improves, but susceptibility to noise and artifacts increases
Solution Approach 1:
The frequency spectrum is segmented into multiple bands (delta, theta, alpha, beta, gamma, and high-gamma) with dedicated amplification and filtering for each band. This allows optimal gain to be applied to each frequency range separately, enhancing sensitivity to low-amplitude signals while using band-specific filtering to reject out-of-band noise and artifacts.
Solution Approach 2:
Analog filtering is performed preliminarily in the front-end circuitry before amplification and digitization. Band-pass filters are implemented to pre-select the frequency range of interest, which reduces the amplitude of out-of-band noise and artifacts before they can be amplified, thereby improving signal-to-noise ratio for low-amplitude brain signals.
4Measurement precision
If multiple wires and connectors are used for EEG cap, then signal acquisition is possible, but portability and flexibility are reduced
Solution Approach 1:
Multiple signal paths from multiple electrodes are merged into a single digital data stream through time-division multiplexing. Each electrode channel is sequentially sampled and digitized, then combined into one digital output that contains all EEG signals. This merging eliminates the need for multiple analog wires and connectors, enabling wireless and portable EEG systems.
Solution Approach 2:
The mechanical system of multiple wires and connectors is replaced with an electronic/digital system. Analog signals from multiple electrodes are sequentially multiplexed and converted to digital form, then transmitted through a single digital interface or wirelessly. This substitution eliminates mechanical constraints and enables portability while maintaining full signal acquisition capability.
Data Source
AI summary
This invention discloses a non-invasive electroencephalography (BEG) signal recorder and a multiband active electrode (MAE) EEG cap array. A narrow-band amplification method is disclosed that divides the desired bandwidth of the input brain signal to smaller bands, each recorded using a separate amplification path. A novel twisted differential feedback topology is disclosed for both amplifiers and active filters having ultra-high input impedance. A one-wire EEG cap array of tightly connected MAEs is disclosed that improves the flexibility and portability of the EEG cap by reducing the number of wires between the EEG cap and the host processor. Due to having MAEs embedded inside electrodes, the output signals of electrodes are digital information. The tightly connected network of MAEs enables the reference electrode to be chosen dynamically. Moreover, the voltage of the reference node is adjusted using a correction feedback loop before each recording step.