Stimulator DAC Circuitry With Nonlinear Current Resolution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing implantable pulse generator (IPG) devices for neurostimulation, such as spinal cord stimulation (SCS) and deep brain stimulation (DBS), face challenges in providing flexible and precise current adjustments at the electrodes, particularly due to the constant current increment in the Digital-to-Analog (DAC) circuitry, which is not optimal for varying therapeutic current needs.
Innovation Solution
The proposed solution involves a more flexible DAC circuitry design that allows the output current to vary non-linearly with the amplitude value, using different circuits with distinct current-voltage characteristics, such as resistors, MOS diodes, and p-n diodes, to set the relationship between the output current and amplitude, thereby providing a constant or more consistent resolution over the dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If constant current increment DAC circuitry is used, then the device structure is simple, but the current adjustment precision is insufficient for varying therapeutic needs
Solution Approach 1:
The patent implements dynamic current increment adjustment by providing multiple DAC circuitry configurations (first DAC with first current increment, second DAC with second current increment) that can be selectively activated based on the desired current range. This allows the system to transition from fixed to dynamic increment behavior, improving adjustment precision without requiring a completely complex new architecture.
Solution Approach 2:
The patent changes the parameter of current increment value by providing different DAC circuitry options with different increment characteristics. The system can select between first DAC circuitry with a first current increment and second DAC circuitry with a second current increment, thereby adapting the precision parameter to match therapeutic requirements without redesigning the entire system.
2Adaptability or versatility
If multiple DAC circuitries with different current increments are provided, then the current adjustment flexibility is improved, but the device complexity increases
Solution Approach 1:
The patent achieves multi-functionality by incorporating both first DAC circuitry and second DAC circuitry within the same device, where each DAC serves different therapeutic current ranges or adjustment needs. This universal design allows a single device to handle diverse stimulation requirements, from fine adjustments in low-current regimes to coarser adjustments in high-current regimes, without requiring multiple separate devices.
Solution Approach 2:
The patent segments the current adjustment function by dividing the DAC circuitry into distinct first and second DAC modules, each with different current increment characteristics. This segmentation allows independent optimization of each module for its specific function while maintaining overall system flexibility through selective activation based on therapeutic needs.
3Measurement precision
If non-linear current variation is implemented, then the resolution consistency over dynamic range is improved, but the circuit design complexity increases
Solution Approach 1:
The patent introduces intermediate control logic that mediates between the digital control signal and the analog current output by selectively activating different DAC circuitries. This intermediary layer manages the complexity of non-linear current variation by coordinating between multiple DAC modules, ensuring smooth transitions and consistent resolution across the full dynamic range without requiring a completely new circuit architecture.
Data Source
Figure 1~2B
Figure 3A
Figure 3B
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.