Implantable Stimulator Current Steering With Master DAC Distribution
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Solution Overview
Problem
Current implantable pulse generators (IPGs) for spinal cord stimulation systems face challenges in efficiently managing and distributing stimulation currents across multiple electrodes, leading to potential inefficiencies and suboptimal therapy delivery due to the complexity of existing circuit architectures.
Innovation Solution
The development of a pulse generator architecture that includes a centralized master digital-to-analog converter (DAC) to set the amplitude of stimulation currents and a distributor to scale and distribute these currents to dedicated PDAC/NDAC pairs for each electrode, allowing for precise control and distribution of anodic and cathodic currents across the electrode array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a traditional IPG architecture with separate microcontroller and ASIC is used, then the device can provide basic stimulation functionality, but the circuit complexity increases and current distribution efficiency decreases
Solution Approach 1:
The patent combines the microcontroller and ASIC into a single integrated circuit, merging previously separate control and stimulation functions. This integration reduces the number of discrete components and interconnections, thereby reducing circuit complexity while maintaining full functionality for multi-electrode stimulation and current distribution control.
Solution Approach 2:
The integrated circuit is designed to perform multiple functions including microcontroller operations, DAC conversions, and stimulation current generation within a single device. This multi-functionality eliminates the need for separate dedicated circuits for each function, reducing overall system complexity while improving current distribution efficiency through centralized control.
2Measurement precision
If multiple DACs are used for each electrode to enable precise current control, then stimulation precision improves, but the device complexity and power consumption increase
Solution Approach 1:
The patent segments the current control function by implementing a single master DAC that generates a common amplitude signal, which is then distributed to multiple electrode-specific DACs. Each electrode DAC receives the same reference amplitude but independently controls its own current magnitude through separate control signals, enabling precise individual electrode control while sharing the power-intensive master DAC functionality.
Solution Approach 2:
The master DAC acts as an intermediary that provides a shared amplitude reference to multiple electrode DACs. This intermediary approach allows all electrodes to benefit from high-precision current control through the master DAC's accurate amplitude generation, while the individual electrode DACs only need to perform simpler current division based on control signals, reducing overall power consumption compared to fully independent high-precision DACs for each electrode.
3Loss of energy
If a centralized master DAC is implemented to control all electrode currents, then power efficiency improves, but the ability to independently control each electrode's current amplitude may be limited
Solution Approach 1:
The current control system is segmented into a master DAC that sets overall amplitude and electrode-specific DACs that control individual electrode current distribution. The master DAC receives a single amplitude control signal and generates a shared reference, while each electrode DAC receives both the shared reference and its own independent control signal, enabling flexible independent control of each electrode's current magnitude while maintaining power efficiency through the shared master DAC.
Solution Approach 2:
The system dynamically adjusts current distribution by allowing the master DAC to set the overall amplitude envelope while electrode-specific control signals dynamically divide and allocate this current to individual electrodes. This dynamic control architecture enables versatile independent adjustment of each electrode's current amplitude in real-time, maintaining adaptability while benefiting from the power efficiency of a centralized amplitude reference.
Data Source
Figure 1A~1C
Figure 2A
Figure 2B
AI summary
An implantable pulse generator (IPG) is disclosed having an improved ability to steer anodic and cathodic currents between the IPG's electrodes. Each electrode node has at least one PDAC/NDAC pair to source/sink or sink/source a stimulation current to an associated electrode node. Each PDAC and NDAC receives a current with a magnitude indicative of a total anodic and cathodic current, and data indicative of a percentage of that total that each PDAC and NDAC will produce in the patient's tissue at any given time, which activates a number of branches in each PDAC or NDAC. Each PDAC and NDAC may also receive one or more resolution control signals specifying an increment by which the stimulation current may be adjusted at each electrode. The current received by each PDAC and NDAC is generated by a master DAC, and is preferably distributed to the PDACs and NDACs by distribution circuitry.