Chopped Neural Recording Front-End With Boosted Input Impedance
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Solution Overview
Problem
High precision electronics with choppers in front-end circuitry suffer from low input impedance due to switching, limiting the frequency range detectable by the circuit, as the coupling capacitors need to be charged by the input source, which decreases input impedance with increasing switching frequency.
Innovation Solution
A neural recording system with a front-end that includes two choppers and multiple capacitors, where the choppers are configured to keep the coupling capacitors charged to a consistent voltage, boosting the input impedance by cross-coupling sensor electrode and feedback subsystem outputs to the choppers, allowing the amplifier to receive error differences and amplify them to tune the feedback signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If choppers switch at high frequency to improve signal processing, then signal processing performance is improved, but input impedance decreases
Solution Approach 1:
The patent divides the single chopper into two separate choppers operating at different phases. The first chopper processes the positive half-cycle of the signal while the second chopper processes the negative half-cycle. This segmentation allows each chopper to operate independently, reducing the overall impact on input impedance while maintaining high-frequency signal processing capability.
Solution Approach 2:
The patent implements periodic switching of two choppers where each chopper operates during alternating half-cycles of the input signal. The first chopper is active during one half-cycle and the second chopper is active during the opposite half-cycle. This periodic action maintains continuous signal processing while distributing the impedance impact across different time periods, effectively boosting the overall input impedance.
2Ease of operation
If coupling capacitors are used to couple chopper to amplifier, then signal transmission is enabled, but input impedance is lowered due to capacitor charging current
Solution Approach 1:
The patent segments the coupling capacitor function across two separate capacitors, each associated with a different chopper. The first coupling capacitor couples the first chopper to the amplifier during one half-cycle, while the second coupling capacitor couples the second chopper to the amplifier during the opposite half-cycle. This segmentation distributes the charging current demand, reducing the overall impact on input impedance.
Solution Approach 2:
The patent uses periodic switching to alternately charge the first and second coupling capacitors during different half-cycles. During the period when the first chopper is active, the first coupling capacitor is charged; during the period when the second chopper is active, the second coupling capacitor is charged. This periodic charging pattern reduces the instantaneous current demand compared to a single capacitor system, thereby boosting input impedance.
3Object-affected harmful factors
If high input impedance is maintained to protect tissue, then tissue safety is improved, but frequency range detection is limited
Solution Approach 1:
The patent employs periodic switching of two choppers operating at different phases to maintain high input impedance while enabling wide frequency range detection. The alternating operation ensures continuous signal processing across different frequency ranges without requiring the input impedance to drop, thus protecting tissue while maintaining adaptability.
Solution Approach 2:
The patent changes the operational parameters by using two choppers with different switching phases and two coupling capacitors with different charging patterns. This parameter change allows the system to maintain high input impedance across a broader frequency range, simultaneously achieving tissue protection and extended detection capability.
Data Source
AI summary
Described herein is a front-end for a neural recording system that boosts input impedance of the front-end circuit. The front-end includes an amplifier and two choppers. A first input terminal of the first chopper may be coupled to a first output terminal from one or more signal sensors. A first input terminal of the second chopper may be coupled to a second output terminal from the signal sensors. A second input terminal of the first chopper may be coupled to a first output terminal of a feedback subsystem. A second input terminal of the second chopper may be coupled to a second output terminal of the feedback subsystem. The output terminals of each chopper may each be coupled to a different capacitor such that after switching, the voltage of each capacitor remains substantially the same, improving the input impedance of the circuit.