Neuromodulation Amplifier Circuit With Common-Mode Suppression
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Solution Overview
Problem
Conventional neuromodulation devices suffer from common mode interference (CMI) due to their limited common mode range, which can lead to amplification failure when handling high-frequency neural stimulation signals.
Innovation Solution
The proposed amplifier circuit incorporates a CM amplifier that combines and amplifies first and second CM voltage signals with an inverting gain, providing an inverted CM voltage signal to the transconductor to suppress CM voltage signals and reduce CMI, while maintaining low noise performance and rejecting large electrode DC offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional amplifier circuit is used for neural recording, then low-noise small-signal amplification can be achieved, but the circuit suffers from common mode interference when handling high-frequency neural stimulation signals
Solution Approach 1:
The amplifier circuit is segmented into separate functional blocks: a differential inverter-based transconductor for low-noise amplification and a dedicated CM amplifier for common mode interference suppression. This segmentation allows each block to optimize its function independently, resolving the contradiction between maintaining low-noise performance and suppressing CMI.
Solution Approach 2:
A CM amplifier is introduced as an intermediary component between the input stage and the output. This CM amplifier detects and suppresses common mode voltage signals before they can interfere with the main amplification path, while the differential transconductor continues to provide low-noise amplification for the differential signal.
2Object-affected harmful factors
If a CM feedforward amplifier is inserted to suppress common mode voltage, then CMI can be reduced, but the input impedance is degraded and chip area increases
Solution Approach 1:
The CM suppression functionality is merged with the existing amplifier structure by using the same input capacitors and transconductor nodes for both differential signal processing and common mode detection. The CM amplifier shares the same power supply and process technology, eliminating the need for separate dedicated components and reducing overall chip area.
Solution Approach 2:
The input capacitors and transconductor nodes serve dual purposes: they are part of the main signal path for low-noise amplification and simultaneously serve as the input stage for the CM amplifier. This multi-functionality reduces the total component count and chip area while maintaining CMI suppression capability.
Data Source
Figure 1(a)~1(c)
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AI summary
This disclosure provides a neuromodulation device for measuring a biological electrical signal in response to a neural modulation of biological tissue. The neuromodulation device comprises at least one amplifier circuit (20), which is used to amplify an input voltage signal that is based on the biological electrical signal. The amplifier circuit (20) suppresses a common mode (CM) voltage signal in the input voltage signal. The amplifier circuit (20) comprises an input stage (21) to receive the input voltage signal, and a differential transconductor (23) to provide an output current signal based on a DM voltage signal in the input voltage signal. The transconductor (23) provides a first CM voltage signal and a second CM voltage signal to a CM amplifier (27) of the amplifier circuit (20). The CM amplifier (27) combines the first CM voltage signal with the second CM voltage signal with an inverting gain, and provides the inverted CM voltage signal back to the transconductor (23) for enabling the CM suppression.