MOSFET Resistance Circuit With Temperature Compensation for Implants
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Solution Overview
Problem
Existing CMOS analog circuit designs for implantable medical devices face challenges in providing temperature-stable resistance values due to significant space requirements and inadequate temperature compensation, which is crucial for stable communication and operation within varying patient temperatures.
Innovation Solution
A circuit arrangement using MOSFET transistors with temperature-dependent reference currents and output voltages that cancel out temperature dependencies, resulting in a temperature-compensated output resistance, achieved by carefully dimensioning the transistors to operate in specific regions and using current mirrors for equal temperature dependencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If poly-resistances are used to provide temperature-independent resistance, then temperature stability is improved, but space or area requirements increase significantly
Solution Approach 1:
The patent changes the operating parameters of MOSFET transistors by applying temperature-dependent bias voltages and currents to compensate for temperature variations in resistance. Instead of using physical poly-resistances, the invention uses electrical parameter modulation (gate voltages, drain currents) to achieve temperature-independent resistance characteristics in standard CMOS transistors, thereby reducing area while maintaining stability.
Solution Approach 2:
The patent replaces physical resistance structures (poly-resistances) with an active circuit implementation using MOSFET transistors controlled by temperature-compensating bias circuits. This substitution transforms a passive physical component into an active electronically-controlled system, achieving the same temperature stability function with reduced area overhead.
2Area of stationary object
If standard CMOS transistors are used for resistance implementation, then space efficiency is improved, but temperature independence deteriorates due to temperature variations within the patient
Solution Approach 1:
The patent implements feedback mechanisms where temperature-dependent reference currents and bias voltages are generated based on the actual temperature conditions and fed back to the MOSFET transistors. The bias circuits continuously adjust the operating parameters of the transistors to compensate for temperature drift, creating a closed-loop system that maintains temperature-independent resistance despite environmental temperature variations.
Solution Approach 2:
The patent transforms static resistance values into dynamic, adaptively-controlled resistance characteristics. The MOSFET transistors operate in dynamically adjusted bias conditions where gate voltages and drain currents are continuously modulated according to temperature conditions, enabling the resistance to adapt its behavior to maintain stability across varying temperatures rather than relying on fixed physical properties.
3Stability of the object's composition
If temperature compensation circuits are added to achieve temperature-independent resistance, then temperature stability is improved, but device complexity increases
Solution Approach 1:
The patent merges the temperature compensation function with the primary resistance implementation function by using the same MOSFET transistors for both purposes. The bias circuits generate temperature-dependent reference currents that simultaneously serve as operating currents for the resistance-implementing transistors, combining multiple functions into unified circuit blocks rather than adding separate compensation stages.
Solution Approach 2:
The patent creates multi-functional circuit blocks where MOSFET transistors serve dual purposes: implementing the desired resistance function while simultaneously participating in temperature compensation through their biasing arrangements. The reference current circuits and bias generation circuits are designed to serve multiple functions including temperature sensing, compensation signal generation, and direct resistance implementation, reducing overall circuit complexity through functional integration.
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
The solution provides a temperature-independent output resistance, ensuring stable operation and efficient use of space and power in implantable medical devices, particularly in communication circuits, by compensating for temperature variations.
Implementation Method 1
a first circuit portion configured to supply a temperature-dependent reference current to the first MOSFET transistor, and a second circuit portion configured to generate a temperature-dependent output voltage across a drain and a source of the first MOSFET transistor, such that an ON resistance of the first MOSFET transistor resulting from the output voltage and the reference current provides the temperature-compensated output resistance
Data Source
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AI summary
A circuit arrangement (140-144) for use in an implantable medical device (1) is configured for providing a temperature-compensated output resistance and comprises a first MOSFET transistor (M3), a first circuit portion configured to supply a temperature-dependent reference current (IREF) to the first MOSFET transistor (M3), and a second circuit portion configured to generate a temperature-dependent output voltage (VR) across a drain (D) and a source (S) of the first MOSFET transistor (M3), such that an ON resistance (RON,M3) of the first MOSFET transistor (M3) resulting from the output voltage (VR) and the reference current (IREF) provides the temperature-compensated output resistance.