Pulse-by-Pulse Compliance Voltage Control in Implantable Stimulators
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Solution Overview
Problem
Implantable stimulation devices 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, leading to sub-saturation or unnecessary power wastage.
Innovation Solution
The implementation of improved compliance voltage generation circuitry that assesses and adjusts the voltage drops across active PDACs and NDACs on a pulse-by-pulse basis using differential amplifiers, comparators, and an OR gate to ensure voltage drops remain within optimal ranges, utilizing a V+ regulator to adjust the compliance voltage accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compliance voltage is increased to maintain optimal operation of current sources and sinks, then reliability is improved, but energy consumption increases
Solution Approach 1:
The compliance voltage is made dynamic rather than fixed, allowing it to be adjusted in real-time based on actual tissue resistance conditions. The voltage regulator modifies the compliance voltage level in response to feedback signals that indicate whether the voltage drop across the current source/sink is within the optimal saturation range, thereby maintaining reliable operation only when necessary and reducing energy consumption when conditions permit.
Solution Approach 2:
A feedback mechanism is implemented where the voltage drop across the active current source or sink is monitored and compared against optimal saturation thresholds. Based on this feedback, the system determines whether to adjust the compliance voltage upward or downward, enabling adaptive voltage control that balances reliability with energy efficiency by avoiding unnecessary high voltage application.
2Loss of energy
If compliance voltage is decreased to reduce power wastage, then energy efficiency is improved, but reliability deteriorates due to sub-saturation conditions
Solution Approach 1:
The compliance voltage is dynamically adjusted based on real-time monitoring of voltage drop conditions. Rather than maintaining a fixed high voltage that causes continuous power wastage, the system lowers the voltage when tissue resistance decreases and the voltage drop exceeds the optimal range, thereby reducing power consumption while only allowing voltage reduction when reliability is not compromised.
Solution Approach 2:
The feedback system monitors the voltage drop across the current source/sink and compares it to the optimal saturation range. When the voltage drop is too high (indicating excessive power wastage), the feedback signal triggers a reduction in compliance voltage. This ensures that voltage is decreased only when conditions allow, maintaining reliability while improving energy efficiency.
3Reliability
If compliance voltage is continuously adjusted to maintain optimal voltage drops, then reliability is improved, but device complexity increases
Solution Approach 1:
The voltage regulation function is segmented into distinct modular components: a voltage regulator for adjusting compliance voltage, a monitoring circuit for measuring voltage drops, a comparison circuit for evaluating against thresholds, and a control logic unit for decision-making. This segmentation allows each component to perform a specific function simply, reducing overall complexity while achieving reliable continuous adjustment.
Solution Approach 2:
An intermediary control mechanism is introduced that mediates between the monitoring of voltage conditions and the adjustment of compliance voltage. This intermediary layer processes the feedback information and translates it into appropriate voltage regulation actions, simplifying the control logic and making the overall system more manageable despite the continuous adjustment requirement.
4Reliability
If compliance voltage is fixed at high level to ensure saturation, then reliability is improved, but energy efficiency deteriorates
Solution Approach 1:
The system transitions from fixed high compliance voltage to dynamic voltage adjustment. The compliance voltage is continuously monitored and adjusted based on actual tissue resistance conditions, maintaining saturation (reliable operation) only when tissue resistance requires it, and reducing voltage when tissue resistance is low, thereby eliminating unnecessary power consumption while preserving reliability when needed.
Solution Approach 2:
Feedback control is implemented to replace fixed high voltage operation. The system continuously monitors the voltage drop across the current source/sink and uses this feedback to adjust the compliance voltage dynamically. This ensures saturation conditions are maintained only when necessary for reliable operation, rather than continuously, thereby significantly reducing energy waste during periods when high voltage is not required.
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.