Stimulator DAC Circuitry With Nonlinear Current Adjustment
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Solution Overview
Problem
Existing Digital-to-Analog (DAC) circuitry in implantable neurostimulator devices provides current adjustments with a linear increment that is too coarse for lower currents and too fine for higher currents, leading to suboptimal therapy adjustments.
Innovation Solution
The implementation of DAC circuitry with non-linear amplitude adjustment, allowing for parabolic, exponential, or linear variation of output current magnitude based on amplitude values, enabling finer adjustments at lower currents and coarser adjustments at higher currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If linear amplitude adjustment is used in DAC circuitry, then the current adjustment is simple and consistent across the range, but the adjustment is too coarse for lower currents and too fine for higher currents
Solution Approach 1:
The patent applies dynamics by making the DAC circuitry adjustable between different amplitude adjustment modes (linear, parabolic, exponential) depending on the therapeutic needs. The system dynamically adapts the adjustment characteristic based on the operating range, allowing coarse adjustments at high currents and fine adjustments at low currents, thus resolving the contradiction between simplicity and precision.
Solution Approach 2:
The patent changes the adjustment parameter characteristic from fixed linear to variable (parabolic or exponential) based on the amplitude value range. By modifying the mathematical relationship between digital code and analog output, the system achieves both coarse adjustment capability at high currents and fine adjustment capability at low currents, resolving the precision-simplicity contradiction.
2Measurement precision
If non-linear amplitude adjustment is implemented, then finer current control is achieved at lower currents, but the circuit complexity increases
Solution Approach 1:
The patent implements multi-functionality by designing the DAC circuitry to perform multiple adjustment modes (linear, parabolic, exponential) within a single integrated circuit. This allows the system to achieve fine current control precision across different ranges without requiring separate circuits for each mode, thus managing the complexity while maintaining high precision.
Solution Approach 2:
The system dynamically selects the appropriate adjustment mode based on the operating range requirements. By making the circuit adaptable rather than fixed, the patent achieves high precision control where needed while avoiding unnecessary complexity in other operating conditions, effectively managing the precision-complexity trade-off.
3Adaptability or versatility
If multiple amplitude adjustment modes are provided, then therapeutic flexibility is enhanced, but the control system complexity increases
Solution Approach 1:
The patent integrates multiple amplitude adjustment modes (linear, parabolic, exponential) into a single universal DAC control system. This multi-functional design allows the implantable device to adapt to different therapeutic requirements without requiring separate control systems for each mode, thus enhancing therapeutic flexibility while managing control system complexity through integration.
Data Source
AI summary
Digital-to-Analog Converter (DAC) circuitry useable in a stimulator device is disclosed. The DAC circuitry produces an output current whose magnitude varies as a function of an amplitude value provided by a digital amplitude bus. The relationship of the output current to the amplitude (Iout(A)) may be linear or non-linear depending on the current-voltage characteristics of a circuit in the DAC that is selected for use. For example, if a resistor is selected, the output current will vary linearly with amplitude; if a p-n diode is selected, the output current will vary exponentially with amplitude. The shape of Iout(A) affects the resolution of the output current, and depending on the circuit selected, can cause the resolution to be constant, or at least more constant, over the dynamic range of the DAC circuitry. The DAC circuitry is further beneficial in its ability to be programmed with a minimum and maximum output current.