Dual Electrothermal Filter Phase Sensing Without Frequency Reference
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Solution Overview
Problem
Existing ETF-based temperature sensors and EFLL-based frequency references face limitations due to their dependence on accurate frequency references and temperature compensation, which are often unavailable in applications like automotive, industrial, and space sectors, leading to inaccuracies and increased measurement errors.
Innovation Solution
A device incorporating two electrothermal filters with different temperature-dependent time constants and a phase detector, allowing for self-referenced temperature sensing and frequency reference generation without external time or frequency references, using a drive circuit to generate signals with fundamental frequencies and phases relative to these time constants, and compensating for temperature-dependent frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single ETF is used for temperature sensing, then the device can operate, but measurement accuracy is limited due to temperature-dependent time constant variations
Solution Approach 1:
The patent uses two ETFs with different time constants (τ1 and τ2) to create a ratio-based measurement system. By forming the ratio φ1/φ2 of phase shifts from two ETFs with different temperature dependencies, the system cancels out common-mode temperature variations and achieves temperature-independent measurement, thereby improving both accuracy and reliability under temperature variations.
Solution Approach 2:
The system combines two different ETF structures (with different thermal masses or geometries) to create a composite measurement system. Each ETF contributes differently to the overall measurement, and their combined ratio output provides temperature compensation, similar to how composite materials combine different properties to achieve superior performance.
2Measurement precision
If external frequency references are used for ETF-based sensing, then measurement accuracy can be maintained, but the device cannot operate stand-alone in applications without available frequency references
Solution Approach 1:
The patent makes the ETF system self-sufficient by using the ratio of phase shifts from two ETFs with different time constants as the measurement output. This ratio is inherently independent of the drive frequency, eliminating the need for external frequency references and enabling stand-alone operation in applications like automotive, industrial, and space sectors where such references may not be available.
Solution Approach 2:
By changing the measurement parameter from absolute phase shift (which requires frequency reference) to phase shift ratio between two ETFs, the system achieves frequency independence. The ratio φ1/φ2 remains constant regardless of drive frequency variations, allowing the device to operate autonomously without external frequency references.
3Measurement precision
If temperature compensation circuits are added to ETF-based frequency references, then frequency accuracy improves, but device complexity increases
Solution Approach 1:
The patent changes the fundamental measurement parameter from absolute phase shift to phase shift ratio, which inherently provides temperature compensation. This approach achieves temperature-independent frequency reference without requiring additional temperature sensors, ADCs, or complex compensation circuits, thereby maintaining high accuracy while minimizing device complexity.
Solution Approach 2:
The two-ETF system performs self-compensation for temperature variations through its ratio-based output. The different temperature dependencies of the two ETFs naturally cancel out temperature effects in the ratio, eliminating the need for external temperature compensation circuits and reducing overall system complexity.
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 highly accurate temperature sensing and frequency references with reduced measurement errors, facilitating stand-alone operation and improved accuracy in various applications, including those without readily available accurate frequency references.
Implementation Method 1
heat pulses, which are continuously generated at a fundamental frequency fdrive, diffuse through the silicon and create low-pass-filtered temperature fluctuations across the thermopile
Implementation Method 2
The thermopile converts these temperature fluctuations into a signal VETF with a phase shift φETF (relative to fdrive)
Implementation Method 3
the device-to-device spread of this thermal delay is mainly a function of the lithographic inaccuracy with which s can be defined
Data Source
AI summary
During operation of the device, a drive circuit may provide a drive signal having a fundamental frequency to two electrothermal filters (ETFs) having different temperature-dependent time constants. In response to the drive signal, the two ETFs may provide signals having the fundamental frequency and phases relative to the drive signal corresponding, respectively, to the time constants of the ETFs. Then, phase-shift values of the phases may be measured using a phase detector, and a signal may be output based on the phase-shift values. Note that the signal may correspond to a value that is a function of a temperature of the device.