Charge Imbalanced Pulses for Pseudo-Constant DC Current in Implantable Stimulators
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Solution Overview
Problem
Implantable neurostimulator devices face challenges in providing direct current (DC) stimulation due to safety concerns, such as electrode corrosion and tissue damage, and the presence of DC-blocking capacitors that inhibit DC current delivery.
Innovation Solution
The use of charge imbalanced pulses that charge capacitances in the current path, allowing a pseudo-constant DC current to flow during quiet periods between active phases, while maintaining safety through DC-blocking capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC current is delivered to tissue through implantable electrodes, then therapeutic effect is improved, but electrode corrosion and tissue damage occur
Solution Approach 1:
The patent employs periodic pulsed current delivery instead of continuous DC current. The stimulator delivers current in discrete pulses with active phases followed by quiet periods, which allows capacitances to charge and discharge cyclically. This periodic action achieves therapeutic effects while limiting total charge transfer to safe levels that prevent electrode corrosion and tissue damage.
Solution Approach 2:
The patent changes the electrical parameters of current delivery by using charge imbalanced pulses with specific amplitude and duration relationships. The positive and negative phases of each pulse are designed with different charge magnitudes (Q+ ≠ Q-), creating a net charge transfer that establishes DC bias while maintaining peak currents within safe therapeutic limits. This parameter optimization resolves the contradiction between achieving therapeutic DC effects and preventing harmful electrode/tissue interactions.
2Reliability
If DC-blocking capacitors are used in the stimulator circuit, then safety is improved, but DC current delivery is inhibited
Solution Approach 1:
The patent uses the DC-blocking capacitors to preliminarily store charge during active phases of the pulsed waveform. The capacitors charge up during the high-current active phases and then discharge during the quiet periods between pulses, creating the pseudo-constant DC current flow. This preliminary charge storage action allows the capacitors to enable rather than inhibit DC delivery, resolving the contradiction by utilizing their charge-blocking property in a creative temporal sequence.
Solution Approach 2:
The patent converts the harmful effect of DC-blocking capacitors (which normally prevent DC current flow) into a beneficial mechanism. By deliberately using charge imbalanced pulses, the capacitors' charge accumulation during active phases creates the desired DC bias current during quiet periods. The very property that was considered harmful (charge blocking) becomes the mechanism for achieving safe DC delivery, as the capacitors naturally discharge their stored charge in a controlled manner that prevents both DC damage and enables therapeutic effect.
3Productivity
If charge imbalanced pulses are used to create pseudo-constant DC current, then DC current delivery is improved, but charge imbalance between positive and negative phases must be precisely controlled
Solution Approach 1:
The patent incorporates feedback mechanisms through programmable control of pulse parameters. The stimulator can adjust the amplitude and duration of positive and negative phases based on measured tissue impedance and charge transfer. This feedback allows precise control of the charge imbalance (Q+ - Q-) to maintain the pseudo-constant DC current within therapeutic ranges while automatically compensating for variations in tissue properties, thereby resolving the precision control challenge.
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
This approach enables therapeutic DC current delivery without causing tissue damage or electrode corrosion, while ensuring safety by utilizing existing DC-blocking capacitors.
Implementation Method 1
The use of charge imbalanced pulses that charge capacitances in the current path, allowing a pseudo-constant DC current to flow during quiet periods between active phases
Data Source
AI summary
Techniques are described for providing a therapeutic pseudo-constant DC current in an implantable stimulator using pulses whose positive and negative phases are not charge balanced. Such charge imbalanced pulses act to charge any capacitance in the current path between selected electrode nodes, such as the DC-blocking capacitors and/or any inherent capacitance such as those present at the electrode/tissue interface. These charged capacitances act during quiet periods between the pulses to induce a pseudo-constant DC current. Beneficially, these DC currents can be small enough to stay within charge density limits and hence not corrode the electrode or cause tissue damage, and further can be controlled to stay within such limits or for other reasons. Graphical user interface (GUI) aspects for generating the charge imbalanced pulses and for determining and/or controlling the pseudo-constant DC current are also provided.