Implantable Stimulator Compliance Voltage Control for Pulse Efficiency
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Solution Overview
Problem
Implantable stimulators face challenges in maintaining optimal compliance voltage for current sources and sinks, which is crucial for efficient operation and energy efficiency, as tissue resistance changes due to patient movement or other factors can alter the voltage drops across electrodes, potentially leading to sub-saturation or unnecessary power wastage.
Innovation Solution
The implementation of improved compliance voltage generation circuitry that assesses voltage drops across active PDACs and NDACs on a pulse-by-pulse basis, using differential amplifiers, comparators, and an OR gate to adjust the compliance voltage (V+) to keep it at optimal levels by enabling or disabling a V+ regulator, ensuring efficient operation of DACs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the compliance voltage is increased to ensure sufficient voltage headroom for current delivery, then the current sources and sinks can maintain saturation operation, but power consumption increases unnecessarily when tissue resistance is low
Solution Approach 1:
The patent implements dynamic compliance voltage adjustment by monitoring the actual voltage drops across current sources and sinks during pulse delivery. The system continuously adapts the compliance voltage level based on real-time tissue resistance conditions, transitioning from static to dynamic voltage regulation. This allows the system to maintain sufficient voltage headroom only when necessary, reducing power consumption during low-resistance conditions while ensuring reliable current delivery when resistance increases.
Solution Approach 2:
The patent employs feedback mechanisms by measuring the actual voltage drops across active current sources and sinks using differential amplifiers and comparators. These measurements feed back to the compliance voltage control logic, which adjusts the voltage level accordingly. The feedback loop ensures that the compliance voltage is optimized based on actual operating conditions, preventing both power wastage and current delivery failures.
2Loss of energy
If the compliance voltage is decreased to minimize power consumption, then energy efficiency improves, but the voltage headroom becomes insufficient leading to sub-saturation operation of current sources and sinks
Solution Approach 1:
The system dynamically adjusts compliance voltage based on real-time monitoring of voltage drops across current sources and sinks. When tissue resistance increases and voltage drops approach critical levels, the system automatically increases compliance voltage to maintain saturation operation. This dynamic response prevents sub-saturation conditions while minimizing power consumption during normal low-resistance operation.
Solution Approach 2:
The feedback mechanism monitors the actual voltage drops during pulse delivery and compares them against threshold values. When the monitored voltage drops indicate approaching sub-saturation conditions, the feedback signal triggers an increase in compliance voltage. This ensures reliable current delivery is maintained while avoiding unnecessary power consumption during low-resistance conditions.
3Device complexity
If fixed compliance voltage is used to simplify circuit design, then device complexity is reduced, but the system cannot adapt to changing tissue resistance conditions
Solution Approach 1:
The patent transforms the static compliance voltage regulation into a dynamic system that automatically adapts to changing tissue resistance. The monitoring circuitry detects voltage drops across current sources and sinks in real-time, and the control logic adjusts compliance voltage accordingly. This dynamic approach provides adaptability to varying physiological conditions while maintaining relatively simple circuit implementation through efficient use of standard electronic components.
Solution Approach 2:
The system implements feedback-based adaptation by continuously measuring voltage drops across active current sources and sinks. The measured values are fed back to control logic that adjusts the compliance voltage to maintain optimal operation. This feedback mechanism enables the system to adapt to changing tissue resistance conditions automatically, providing versatility without requiring complex programmable or adaptive circuitry.
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 allows for dynamic adjustment of compliance voltage, maintaining efficient current delivery while minimizing power wastage by keeping voltage drops at or near optimal values, even with changes in tissue resistance, thereby ensuring consistent therapy delivery.
Implementation Method 1
a differential amplifier to measure an actual voltage drop across the PDAC by comparing an actual voltage to a reference voltage
Implementation Method 2
a comparator to compare the measured voltage drop to a desired voltage drop and generate a control signal
Implementation Method 3
an OR gate to process the control signal from the comparator to generate a regulator control signal
Implementation Method 4
adjust the compliance voltage by controlling a V+ regulator
Data Source
AI summary
Circuitry for generating a compliance voltage (V+) for the current sources and/or sinks in an implantable stimulator device in disclosed. The circuitry assesses whether V+ is optimal for a given pulse, and if not, adjusts V+ for the next pulse. The circuitry uses amplifiers to measure the voltage drop across active PDACs (current sources) and NDAC (current sinks) at an appropriate time during the pulse. The measured voltages are assessed to determine whether they are high or low relative to optimal values. If low, a V+ regulator is controlled to increase V+ for the next pulse; if not, the V+ regulator is controlled to decrease V+ for the next pulse. Through this approach, gradual changes that may be occurring in the implant environment can be accounted for, with V+ adjusted on a pulse-by-pulse basis to keep the voltage drops at or near optimal levels for efficient DAC operation.