RF Power MOSFET Junction Temperature Calculation via Digital IIR Filter
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Solution Overview
Problem
Existing methods for calculating the junction temperature of RF power MOSFETs in MRI amplifiers are inaccurate due to low precision in analog circuit solutions, which are time-consuming and costly to achieve high accuracy.
Innovation Solution
A digital domain approach using a junction temperature compensation model based on a transient thermal impedance model, with a 2nd order IIR filter structure and a 10KHz sampling frequency, eliminates the limitations of analog circuits by establishing a model that can be realized through software or firmware, improving accuracy without physical analog circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog simulation with transient thermal impedance model is used to calculate junction temperature, then the temperature can be derived without direct physical contact, but the accuracy is low due to low precision of actual electrical elements
Solution Approach 1:
The patent replaces the analog circuit system with a digital signal processing system. Instead of using physical electrical resistors and capacitors to simulate thermal behavior, the invention uses digital filters (IIR or FIR) implemented through software or firmware to calculate junction temperature. This substitution eliminates the precision limitations of physical components while maintaining the thermal modeling capability.
Solution Approach 2:
The patent creates a digital copy of the transient thermal impedance model rather than using physical analog components. The thermal behavior is replicated through mathematical algorithms in the digital domain, where precision is determined by computational accuracy rather than physical component tolerances. This digital copying allows for high-precision temperature calculation without being constrained by manufacturing variations in electrical elements.
2Measurement precision
If high accuracy electrical elements are selected and tested in analog circuit, then measurement precision improves, but time cost increases
Solution Approach 1:
The patent eliminates the time-consuming process of selecting and testing high-precision physical electrical elements by replacing the entire analog circuit approach with digital signal processing. The digital filter coefficients can be calculated and stored without requiring physical component characterization, thus eliminating the time cost associated with component selection and testing while maintaining or improving measurement accuracy.
3Ease of operation
If analog circuit is established for thermal impedance modeling, then junction temperature can be calculated, but device complexity increases due to physical components required
Solution Approach 1:
The patent replaces the complex analog circuit architecture with a streamlined digital processing system. Instead of requiring multiple physical resistors, capacitors, and interconnections to model thermal impedance, the invention uses mathematical algorithms implemented in software or firmware. This reduces device complexity by eliminating physical components while preserving the temperature calculation capability.
4Productivity
If digital domain approach with IIR filter is used, then accuracy improves and time cost reduces, but requires transformation from analog to digital domain
Solution Approach 1:
The patent performs the necessary transformation from analog thermal modeling to digital signal processing by converting the continuous-time thermal impedance model into discrete-time digital filters. This transformation is done once during system design, after which the digital model can be efficiently executed without requiring repeated analog-to-digital conversions during operation, thus achieving high productivity with acceptable initial transformation complexity.
Data Source
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AI summary
There are provided a method and apparatus for calculating the junction temperature of an RF power MOSFET. The method for calculating the junction temperature of an RF power MOSFET, comprising steps of: establishing a transient thermal impedance model of the RF power MOSFET in analog domain; calculating a transfer function in time domain of the transient thermal impedance model using bilinear transformation; establishing a junction temperature compensation model in digital domain based on the transfer function in time domain of the transient thermal impedance model with a sampling frequency and a type of 2nd order IIR filter structure; and calculating the junction temperature of the RF power MOSFET by inputting an actual input to the junction temperature compensation model. The present invention improves accuracy in determining the junction temperature of an RF power MOSFET.