Implantable Pulse DAC with Programmable Slew Rate Control

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Solution Overview

Problem

Current implantable pulse generators (IPGs) face limitations in producing stimulation pulses with controlled slew rates, leading to sharp transitions that cause ringing and unwanted oscillations, making it difficult to generate complex waveform shapes and increasing the complexity and power consumption of the DAC circuitry.

Innovation Solution

The introduction of a programmable master DAC circuitry that includes a slew rate stage, allowing for controlled slew rates at transitions, comprising a DAVC stage, a slew stage, and a current generation stage, which processes digitally-defined pulses to produce analog voltages with programmable slew rates, reducing the need for multiple pulse phases and minimizing power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional DAC circuitry is used to generate stimulation pulses, then the circuitry is simpler and power consumption is lower, but sharp transitions cause ringing and unwanted oscillations

Engineering Contradiction:

Improvesignal qualityVSAvoidDAC circuitry complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The DAC circuitry is segmented into multiple functional stages: a master DAC for generating the basic pulse waveform, a slew rate control stage for managing transition sharpness, and a pulse phase management system. This segmentation allows independent optimization of each stage, reducing overall system complexity while improving signal quality by controlling ringing and oscillations through dedicated slew rate management.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention applies preliminary action by pre-calculating and pre-setting the slew rate parameters before pulse generation. The system determines optimal slew rates in advance based on the desired waveform characteristics, then applies these pre-determined rates during pulse generation. This eliminates the need for complex real-time adjustments during pulse delivery, simplifying the DAC circuitry while maintaining reliable signal quality.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If multiple pulse phases are used to approximate slew rate, then controlled slew transitions can be achieved, but memory requirements and circuit complexity increase

Engineering Contradiction:

Improveslew rate controlVSAvoidmemory requirements

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The invention changes the fundamental parameter approach from using multiple discrete pulse phases to directly controlling the slew rate as a continuous parameter. By implementing a slew rate control stage that directly modulates the transition rate, the system achieves precise slew rate control without needing to store multiple pulse phase definitions in memory, thereby reducing memory requirements while maintaining reliable slew rate control.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If sharp transitions are used in stimulation pulses, then the DAC circuitry is simpler and power consumption is reduced, but ringing and oscillations are generated

Engineering Contradiction:

ImproveDAC circuitry complexityVSAvoidringing and oscillations

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The invention introduces an intermediary slew rate control stage between the master DAC and the output stage. This intermediary component acts as a buffer that smooths the sharp transitions from the DAC, controlling the rate of change to eliminate ringing and oscillations while preserving the essential pulse waveform. This intermediary approach allows the use of simpler DAC circuitry without generating harmful oscillations.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Reliability

If controlled slew rate is implemented, then ringing and oscillations are reduced, but power consumption of the DAC circuitry increases

Engineering Contradiction:

Improvesignal stabilityVSAvoidDAC power consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The invention implements periodic action by applying slew rate control only during the transition phases of the pulse waveform, rather than continuously throughout the entire pulse cycle. The slew rate control is activated periodically at the beginning and end of each pulse where transitions occur, and disabled during the stable plateau regions. This periodic application significantly reduces power consumption compared to continuous slew rate control, while maintaining signal stability during critical transition periods.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS10525253B2Current generation architecture for an implantable medical device including controllable slew rate

Publication Date: 2020.01.07 BOSTON SCI NEUROMODULATION CORP

AI summary

Digital-to-analog converter (master DAC) circuitry is disclosed that is programmable to set a controlled slew rate for pulses that are otherwise defined as having sharp amplitude transitions. For example, when producing a biphasic pulse, the constant amplitude and duration of first and second pulses phases can be defined and provided to the DAC in traditional fashion. Slew rate control signals control a slew rate DAC within the master DAC, which prescribes a slew rate that will appear at sharp transitions of the defined biphasic pulses, i.e., at the beginning of the first phase, at the transition from the first to the second phase, and at the end of the second phase. The slew rate can vary with the duration or frequency of the pulses, with lower slew rates used with longer durations and/or lower frequencies, and with higher slew rates used with shorter durations and/or higher frequencies.