Hearing Aid EEG Electrode Circuit DC Offset Reduction
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Solution Overview
Problem
Existing bio response signal recording technologies face challenges in interference immunity and electrode variability, particularly in achieving high Common Mode Rejection Ratio (CMRR) and Power Supply Rejection Ratio (PSRR), due to strong DC offset voltage and transient spikes introduced by digital-analog converters.
Innovation Solution
The hearing aid employs active electrodes with a right-leg-driven technique, combined with differential electrode channel circuits and DC offset units that include offset storage capacitors and pulse current sources to minimize DC offset voltage and improve CMRR and PSRR, replacing traditional digital-analog converters to reduce noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional digital-analog converters are used to compensate electrode offset voltage, then offset compensation is achieved, but transient spikes are introduced causing harmonic distortion and increased noise
Solution Approach 1:
The patent extracts and removes the problematic digital-analog converter from the feedback loop, replacing it with a purely analog integrator circuit. This eliminates the source of transient spikes and harmonic distortion while maintaining the offset compensation function through continuous analog integration of the error signal.
Solution Approach 2:
The patent introduces an analog integrator as an intermediary element between the amplifier output and the offset compensation mechanism. This integrator smoothly processes the error signal without introducing digital conversion artifacts, acting as a mediator that preserves signal integrity while achieving offset compensation.
2Measurement precision
If high gain amplification is used to amplify weak bio response signals, then signal amplitude is increased, but noise and interference are also amplified
Solution Approach 1:
The patent applies preliminary action by implementing offset compensation and noise filtering before the main amplification stage. The feedback loop with analog integrator pre-corrects offset voltages and reduces interference, ensuring that the subsequent high-gain amplification operates on a cleaner signal with less noise to amplify.
Solution Approach 2:
The patent employs feedback mechanisms where a portion of the amplifier output is fed back through an analog integrator to the input stage. This feedback continuously monitors and corrects offset voltages and reduces interference, allowing high gain amplification while maintaining signal quality by dynamically compensating for noise and distortion.
3Device complexity
If conventional electrode configurations are used, then simplicity is maintained, but common mode interference rejection is insufficient
Solution Approach 1:
The patent introduces asymmetry in the feedback loop configuration by implementing a unilateral feedback path from the amplifier output through the analog integrator to the input stage. This asymmetric feedback arrangement creates differential signaling characteristics that inherently reject common mode interference while maintaining relative simplicity in the electrode placement.
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
The present disclosure relates to a hearing aid comprising a plurality of electrode units (E), where each of the plurality of electrode units (E) includes an electrode (E1, E2) configured to provide an electrical stimulation to a user of the hearing aid (1) and/or to measure a bio response signal of the user; a plurality of electrode channel circuits , where each of the plurality of electrode channel circuits includes: an operational amplifier comprising a first input terminal configured to receive the bio response signal and provide an amplified bio response signal, and the operational amplifier includes a first load input; a first DC offset unit configured to reduce the impact of DC offset in the electrode channel circuit of the plurality of electrode channel circuits by receiving a part of the amplified bio response signal and converting it to a feedback current signal which is transmitted to the first load input for providing balanced drain currents in the operational amplifier.