Sample and Hold Circuit for Implantable Neurostimulator Voltage Monitoring
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Solution Overview
Problem
Implantable neurostimulator devices face challenges in accurately monitoring voltages at electrodes, which is crucial for calculating resistance and setting appropriate compliance voltages, due to limitations in existing sample and hold circuitry that fail to effectively cancel parasitic voltages and provide accurate resistance measurements.
Innovation Solution
The implementation of improved sample and hold circuitry that uses multiplexers to select and store voltages, with capacitors connected in series to cancel parasitic voltages, and a differential amplifier to compute voltage differences, allowing for precise measurement of resistance and voltage drops across electrodes during biphasic or monophasic pulsing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sample and hold circuitry is used to monitor electrode voltages, then the device structure is simple, but the measurement precision is insufficient due to inability to cancel parasitic voltages
Solution Approach 1:
The voltage measurement process is divided into two separate phases: first measuring the sum of parasitic voltages, then measuring the electrode voltage including parasitic voltages. By segmenting the measurement into distinct temporal phases, the circuit can isolate and cancel parasitic components through subtraction, improving measurement precision without requiring complex filtering circuits.
Solution Approach 2:
The circuit performs preliminary measurement of parasitic voltages before the main electrode voltage measurement. By capturing the parasitic voltage component in advance during a calibration phase, the system can subsequently subtract this pre-measured value from the total measurement to obtain the accurate electrode voltage, thereby eliminating parasitic interference.
2Reliability
If voltage monitoring is performed during biphasic pulsing, then compliance voltage setting becomes more accurate, but the device complexity increases due to additional circuit requirements
Solution Approach 1:
The sample and hold circuit operates periodically synchronized with the biphasic pulse train, performing voltage measurements during specific phases of the periodic waveform. By aligning measurements with the periodic structure of therapeutic pulses, the circuit achieves accurate compliance voltage monitoring while using simple switching logic rather than continuous complex circuitry.
Solution Approach 2:
The measurement circuit uses the existing therapeutic pulse waveform itself as the measurement stimulus, eliminating the need for separate test pulse generation circuitry. The same electrodes and current sources used for therapy delivery are utilized for voltage measurement, allowing the system to self-diagnose without additional external components.
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 accurate resistance measurement between electrodes and voltage drop analysis, enhancing the precision and efficiency of compliance voltage setting, thereby improving the performance and safety of implantable neurostimulator devices.
Implementation Method 1
capacitors connected in series to cancel parasitic voltages
Data Source
Figure 1A~1B
Figure 2
Figure 3A
AI summary
Sample and hold circuitry for monitoring electrodes and other voltages in an implantable neurostimulator is disclosed. The sample and hold circuitry in one embodiment contains multiplexers to selected appropriate voltages and to pass them to two storage capacitors during two different measurement phases. The capacitors are in a later stage serially connected to add the two voltages stored on the capacitors, and voltages present at the top and bottom of the serial connection are then input to a differential amplifier to compute their difference. The sample and hold circuitry is particularly useful in calculating the resistance between two electrodes, and is further particularly useful when resistance is measured using a biphasic pulse. The sample and hold circuitry is flexible, and can be used to measure other voltages of interest during biphasic or monophasic pulsing.