Linear Mode Current DAC for Implantable Pulse Generator Power Loss
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Solution Overview
Problem
Implantable pulse generators (IPGs) face challenges in minimizing power usage to extend battery life, as the current digital-to-analog converters (DACs) located in series with the load result in power loss, leading to shortened battery life due to voltage drops.
Innovation Solution
The implementation of output current sources and sinks that operate in a linear mode, utilizing transistors or passive resistors with feedback circuits to minimize drain-to-source voltage drops, and incorporating digital-to-analog converters (DACs) to regulate current efficiently, allowing for reduced power consumption and extended battery life without the need for additional output stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current DACs are placed in series with the load, then current regulation is achieved, but power loss increases due to voltage drops
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary between the DAC and the load. The current mirror circuit copies the DAC output current and feeds it back to the DAC input, allowing the DAC to operate with minimal voltage drop while maintaining accurate current regulation. This intermediary mechanism resolves the contradiction by enabling precise current control without the power loss associated with series placement.
Solution Approach 2:
The patent implements a feedback mechanism where the current mirror circuit feeds back the DAC output current to the input. This feedback loop allows the system to maintain accurate current regulation while the DAC operates in a low-voltage-drop configuration. The feedback mechanism enables the DAC to regulate current effectively without being placed in series with the load, thus reducing power loss.
2Duration of action of stationary object
If battery capacity is increased to extend operation time, then device size increases
Solution Approach 1:
The patent changes the operating parameters of the DAC by using a current mirror feedback configuration that operates at lower voltage drops. This parameter change in the circuit operation allows the same battery capacity to provide extended operation time without requiring additional battery size. The efficient current regulation reduces power consumption, thereby extending battery life without increasing device volume.
3Power
If additional output stages are added to amplify current, then current output capability increases, but device complexity increases
Solution Approach 1:
The patent makes the current mirror circuit serve multiple functions: it acts as both the current regulation mechanism and the signal amplification stage. By designing the current mirror to provide both functions, the patent eliminates the need for separate output amplification stages, thereby reducing device complexity while maintaining high current output capability.
Data Source
AI summary
In one embodiment, the present invention provides an implantable stimulation device that includes output current sources and/or sinks configured to provide an output current for a load (i.e., tissue). The output path of the output current source or sink comprises a transistor which operates in a linear mode instead of a saturation mode. Because operation in a linear mode results in smaller drain-to-source voltage drops, power consumption in the output current source or sink (and hence in the implantable stimulator) is reduced, reducing battery or other power source requirements. Operation in the linear mode is facilitated in useful embodiments by a load in an input path (into which a reference current is sent) and a load in the output path (which bears the output current). The loads can be active transistors or passive resistors. A feedback circuit (e.g., an operational amplifier) receives voltages that build up across these loads, and sends a control signal to the gate of the transistor to ensure its linear operation.