Charge-Balanced Stimulation Circuit With Current Mirror Feedback
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Solution Overview
Problem
Conventional electrical stimulation circuits require complex configurations to accurately control current injection into tissues, leading to design mismatches that can cause tissue damage and inefficiencies.
Innovation Solution
A charge-balanced current-controlled stimulation circuit incorporating a transistor differential pair, current mirrors, sample and hold circuits, and a digital-to-analog converter to precisely control and balance currents, minimizing design mismatches and tissue damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electrical stimulation circuits are used, then current control is achieved, but design mismatches cause tissue damage and reduced reliability
Solution Approach 1:
The patent implements a feedback mechanism where the actual current through the tissue is measured and compared with the desired current. The difference (error signal) is used to adjust the stimulation voltage in real-time, ensuring that the actual current matches the commanded current despite tissue impedance variations. This feedback loop significantly improves tissue safety and current control accuracy.
Solution Approach 2:
The patent replaces complex mechanical/circuit-based current control methods with an electronic control system that uses voltage adjustment and electronic feedback. Instead of using complex current-source circuits, the system uses a voltage source with electronic feedback control to achieve precise current control, simplifying the overall circuit design while improving reliability.
2Device complexity
If simple circuit configurations are used, then device complexity is reduced, but current control accuracy deteriorates due to design mismatches
Solution Approach 1:
The feedback mechanism continuously monitors the actual current and adjusts the control voltage to maintain accurate current control. The feedback loop compensates for circuit mismatches and variations, ensuring high current control accuracy even with a relatively simple circuit configuration.
Solution Approach 2:
The system dynamically adjusts the control voltage parameter based on the feedback error signal. By changing the voltage parameter in real-time rather than relying on fixed circuit parameters, the system achieves high current control accuracy without requiring complex circuit design.
3Productivity
If charge accumulation is allowed, then stimulation efficiency is improved, but irreversible Faradaic reactions cause tissue damage
Solution Approach 1:
The patent employs periodic bipolar pulse stimulation where each stimulation cycle consists of a cathodic phase followed by an anodic phase. The anodic phase serves to balance the charge injected during the cathodic phase, ensuring that no net charge accumulates in the tissue. This periodic charge-balanced approach maintains stimulation efficiency while preventing harmful Faradaic reactions.
Solution Approach 2:
The patent converts the potential harmful effect of charge accumulation into a beneficial charge-balancing mechanism. By deliberately injecting equal and opposite charge in the anodic phase, the system uses the same electrical stimulation mechanism to prevent tissue damage, turning what could be a harmful side effect into a protective feature.
4Duration of action of moving object
If DC current is applied, then continuous stimulation is achieved, but tissue damage occurs due to charge accumulation
Solution Approach 1:
The patent uses periodic bipolar pulses instead of continuous DC current. Each pulse cycle includes a cathodic phase for stimulation and an anodic phase for charge balancing. This periodic approach allows for extended stimulation duration while preventing charge accumulation and tissue damage through the repeated charge-balancing cycles.
Data Source
AI summary
A circuit for charge-balanced current-controlled stimulation. The circuit includes a transistor differential pair, a first current mirror, a second current mirror, and a third current mirror. The transistor differential pair includes a first differential input node, a second differential input node, a first differential output node, a second differential output node, and a common node. The transistor differential pair is configured to generate a first differential current that passes through the first differential output node and a second differential current that passes through the second differential output node. The first current mirror is configured to generate a first mirrored current based on the first differential current. The second current mirror is configured to generate a second mirrored current based on the second differential current. The third current mirror is configured to generate a third mirrored current based on the first mirrored current.