Strain Measurement Using Differently Oriented Ring Oscillators
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Solution Overview
Problem
Existing strain measurement techniques on substrates, such as silicon, are sensitive to mechanical deformation, leading to performance degradation in electronic circuits due to strain-induced parasitic effects, and often require external components like strain gauges and amplifiers, which are not integrated and suffer from inaccuracy and temperature drift.
Innovation Solution
An electric circuitry with ring oscillators in different orientations on the substrate, integrated with a time-to-digital converter, allowing for strain measurement by determining signal propagation delays and oscillation frequencies, providing a monolithic integration of strain sensing with other electronic components on a digital CMOS process, and using ratiometric measurements for compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain measurement is performed using external strain gauges and amplifiers, then strain magnitude can be measured, but the system complexity increases and integration with electronic circuits is poor
Solution Approach 1:
The patent merges the strain sensing function with standard digital CMOS electronic circuits by using ring oscillators whose oscillation frequencies are modulated by strain-induced changes in carrier mobility. This integration eliminates the need for separate strain gauge foils, adhesives, and discrete amplifiers, combining sensing and processing electronics into a single monolithic device that maintains measurement capability while reducing system complexity
Solution Approach 2:
The patent replaces the traditional mechanical strain gauge system with an electronic-based measurement approach. Instead of using mechanical deformation of gauge foils connected to external amplifiers, the invention uses strain-modulated oscillation frequencies of ring oscillators, substituting mechanical sensing with electronic frequency modulation that can be directly processed by digital circuits
2Ease of manufacture
If strain measurement is integrated on the same substrate as electronic circuits, then integration is improved, but temperature drift and accuracy degradation occur due to strain affecting both sensor and electronics
Solution Approach 1:
The patent implements feedback through ratiometric measurement techniques where the strain-dependent oscillation frequency is measured relative to a reference. By forming ratios of oscillation periods or frequencies, common-mode temperature drifts affecting both the sensor and reference circuits are cancelled out, maintaining accuracy while allowing monolithic integration of strain sensing electronics on the same substrate
Solution Approach 2:
The patent changes the measurement parameter from absolute frequency or time measurements to ratiometric comparisons. By measuring the ratio of oscillation periods or frequencies between strained and unstrained paths, the system becomes insensitive to temperature-induced drifts that uniformly affect all oscillators, enabling reliable monolithic integration
3Ease of operation
If analog-to-digital converters and amplifiers are used for signal processing, then signal processing capability is improved, but sensitivity to strain-induced parasitic effects increases
Solution Approach 1:
The patent replaces analog signal processing components (amplifiers and analog-to-digital converters) with fully digital processing of oscillator frequency information. By counting oscillation cycles or measuring period ratios using digital logic, the system eliminates analog parasitic effects while maintaining full signal processing capability through digital frequency and period analysis
4Measurement precision
If strain gauges are glued onto the object of interest, then strain measurement is enabled, but the measurement system becomes less reliable due to adhesive degradation and wiring issues
Solution Approach 1:
The patent enables the substrate itself to serve as the sensing element, with strain-induced changes in carrier mobility directly modulating the oscillation frequencies of integrated ring oscillators. This self-service approach eliminates the need for external strain gauge foils, adhesives, and wiring, as the substrate's own electrical properties are exploited for sensing, thereby removing reliability concerns associated with adhesive degradation and connection failures
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
Enables precise measurement of strain magnitude and direction, reducing sensitivity to strain-induced inaccuracies, allowing for on-chip reference and integrated strain compensation, with low current consumption and fast conversion rates, suitable for various applications including strain monitoring and force sensing.
Implementation Method 1
The propagation delay time of the respective delay elements of the at least one first and second delay chain is dependent on the strain applied to the substrate
Implementation Method 2
The at least one first ring oscillator has a first oscillation frequency being dependent on the direction of a strain applied on the substrate
Data Source
AI summary
In an embodiment an electric circuitry includes at least one first ring oscillator and at least one second ring oscillator being arranged on a substrate in different orientations, a time-to-digital converter having a converter ring oscillator and a processing circuit, wherein a first time is determined by a period duration of at least one first ring oscillator, this period duration depending on the propagation delay time of first delay elements, wherein a second time is determined by a period duration of at least one second ring oscillator, this period duration depending on the propagation delay time of second delay elements, and wherein the processing circuit is configured to determine a magnitude of the strain applied on the substrate based on a first state of the converter ring oscillator at the first time and a second state of the converter ring oscillator the second time.