Charge Balancing Circuit for Functional Electrical Stimulation
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Solution Overview
Problem
Existing charge balancing circuits for functional electrical stimulation of biological tissue face challenges with high power consumption, complexity, required space, and response time, which can lead to tissue and electrode damage due to residual charge accumulation.
Innovation Solution
A charge balancing circuit with an amplifier and a compensation stage, utilizing transistor pairs and differential voltage signals to drive the electrode voltage within a safety range, reducing the need for external components and optimizing power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing charge balancing circuits are used, then charge accumulation is prevented, but power consumption is high
Solution Approach 1:
The charge balancing circuit operates periodically by activating the compensation stage only when residual charge exceeds a threshold, rather than continuously. The circuit monitors electrode voltage and triggers compensation only when needed, reducing unnecessary power consumption while maintaining effective charge balancing.
Solution Approach 2:
The circuit uses the existing electrode voltage signal directly for monitoring and control without requiring external power-intensive components. The compensation current is generated from the available voltage rails, allowing the system to self-regulate with minimal additional power consumption.
2Reliability
If existing charge balancing circuits are used, then charge accumulation is prevented, but circuit complexity is high
Solution Approach 1:
The monitoring and compensation functions are merged into a single integrated circuit block. The same operational amplifiers and transistor structures serve both voltage monitoring and current compensation purposes, eliminating the need for separate external monitoring circuits and reducing overall system complexity.
Solution Approach 2:
The operational amplifiers and transistor pairs are designed to perform multiple functions: voltage amplification, signal inversion, threshold comparison, and compensation current generation. This multi-functionality reduces the total component count and simplifies the circuit architecture.
3Reliability
If existing charge balancing circuits are used, then charge accumulation is prevented, but required space is large
Solution Approach 1:
The compensation stage is nested within the existing stimulator circuit architecture, sharing common voltage rails and control structures. The transistor pairs are arranged in a compact configuration where components are nested within each other's functional blocks, minimizing the overall area occupied by the charge balancing circuit.
4Reliability
If existing charge balancing circuits are used, then charge accumulation is prevented, but response time is slow
Solution Approach 1:
The circuit implements direct voltage feedback from the electrode terminal to the operational amplifiers. When the electrode voltage deviates from the safe range, the feedback signal immediately triggers the compensation stage, enabling rapid response without delayed detection or external intervention.
Solution Approach 2:
The operational amplifiers are continuously monitoring the electrode voltage and are pre-biased to immediately activate the compensation transistors when the voltage threshold is exceeded. This preliminary preparation of the compensation path eliminates activation delays and enables instantaneous response to voltage deviations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution decreases power consumption, complexity, and space requirements while ensuring rapid response to maintain electrode voltage within safe limits, preventing tissue and electrode damage.
Implementation Method 1
an amplifier coupled to the electrode terminal and adapted to amplify and invert the electrode voltage for generating an intermediate voltage
Implementation Method 2
The compensation stage is implemented as a transistor stage with at least two transistor pairs connected in series between a first and a second supply terminal
Implementation Method 3
charge accumulation over time may harm the tissue and lead to electrolysis which may dissolve the electrode
Data Source
AI summary
A charge balancing circuit is adapted to be connected to an electrode and to a stimulation source. The charge balancing circuit has an electrode terminal for receiving an electrode voltage, an amplifier coupled to the electrode terminal and adapted to amplify and invert the electrode voltage for generating an intermediate voltage and a compensation stage. The compensation stage is adapted to generate an output current if the electrode voltage lies outside a specified safety range and to generate the output current depending on the intermediate voltage. The compensation stage is further adapted to supply the output current to the electrode terminal for driving the electrode voltage towards and/or into the safety range.