Implantable Pulse Generator DAC Biasing Across Dual Power Domains
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Solution Overview
Problem
Current implantable pulse generators (IPGs) for spinal cord stimulation systems face challenges in efficiently managing power supply and electrode stimulation, leading to suboptimal delivery of therapeutic currents due to limitations in power domain management and current resolution.
Innovation Solution
The improved IPG architecture incorporates a microcontroller-integrated ASIC with enhanced digital-to-analog converter (DAC) circuitry, utilizing pairs of P-type and N-type transistors in separate power domains to source and sink currents, and a pulse definition circuit to control stimulation pulses, allowing for flexible current management and higher resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single power domain is used for both source and sink circuits, then the device complexity is reduced, but the current resolution and control precision deteriorate
Solution Approach 1:
The patent divides the power supply system into separate power domains (first power domain for source circuit, second power domain for sink circuit) to enable independent voltage control. This segmentation allows each circuit to operate with optimized voltage levels, improving current resolution without requiring a complete redesign of the entire power supply architecture.
Solution Approach 2:
Different power domains are assigned to different functional blocks (source vs. sink circuits) based on their specific requirements. The source circuit operates from the first power domain while the sink circuit operates from the second power domain, allowing each to have locally optimized electrical characteristics for its function.
2Measurement precision
If separate power domains are used for source and sink circuits, then the current control precision is improved, but the device complexity increases
Solution Approach 1:
The DAC circuitry is designed to operate across multiple power domains, serving both source and sink functions. The same DAC architecture can be configured to work with different voltage references (VREF_P for source, VREF_N for sink), reducing the need for completely separate control mechanisms and mitigating the complexity increase.
Solution Approach 2:
Voltage reference circuits (VREF_P and VREF_N) act as intermediaries between the power supply and the DAC circuits. These references provide stable, domain-specific voltage levels that simplify the control of each power domain, reducing the management complexity by providing standardized interface points.
3Measurement precision
If higher resolution DAC circuitry is implemented, then the therapy delivery precision is improved, but the power consumption increases
Solution Approach 1:
The patent implements dynamic voltage scaling where the power supply voltages (VDD_P, VDD_N) can be adjusted based on operational requirements. During low-precision operations or idle states, voltages can be reduced to minimize power consumption, while high-precision therapy delivery activates higher voltage levels, creating a dynamic trade-off between precision and power usage.
Solution Approach 2:
The system changes operating parameters (voltage levels, current levels) based on therapeutic requirements. By adjusting the voltage references and power supply levels dynamically, the system can achieve high resolution when needed while operating at lower power consumption during routine or less demanding therapy delivery phases.
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 solution enables more precise and efficient delivery of therapeutic currents, improving treatment efficacy by allowing for finer control over stimulation parameters and adaptability to varying tissue resistance, thus enhancing patient therapy outcomes.
Implementation Method 1
enhanced digital-to-analog converter (DAC) circuitry, utilizing pairs of P-type and N-type transistors in separate power domains to source and sink currents
Implementation Method 2
P-type and N-type transistors in separate power domains to source and sink currents
Data Source
Figure 1A~1C
Figure 2A
Figure 2B
AI summary
Digital-to-analog converter (DAC) circuitry for providing currents at electrodes of an Implantable Pulse Generator (IPG) is disclosed. The DAC circuitry includes at least one PDAC for sourcing current to the electrodes, and at least one NDAC for sinking current from the electrodes. The PDACs are powered with power supplies VH (the compliance voltage) and Vssh in a high power domain, and the NDACs are powered with power supplies Vcc and ground in a low power domain. VH may change during IPG operation, and Vssh preferably also changes with a fixed difference with respect to VH. Digital control signals to the PDACs are formed (and possibly converted into) the high power domain, and transistors used to build the PDACs are biased in the high power domain, and thus may also change with VH. This permits transistors in the PDACs and NDACs to be made from normal low-voltage logic transistors.