MEMS Resonator Synthesizer With Temperature Frequency Compensation
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Solution Overview
Problem
Microelectromechanical systems (MEMS) resonators exhibit significant frequency fluctuations with temperature changes, making them unsuitable for use as reference oscillators in applications requiring stable frequency signals, such as clocks and communication systems, due to their large thermal expansion coefficients and elastic modulus changes.
Innovation Solution
A synthesizer unit that includes a frequency fluctuation detector and adjuster to stabilize the local oscillation signal frequency by compensating for temperature-induced fluctuations in MEMS resonators, using a combination of a voltage-controlled oscillator, frequency dividers, and a phase/frequency comparator to maintain frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If MEMS resonators are used as reference oscillators, then device size and manufacturing cost are reduced, but frequency stability deteriorates due to large thermal expansion coefficients and elastic modulus changes
Solution Approach 1:
The patent implements a feedback control system where a frequency detector continuously monitors the oscillation frequency of the MEMS resonator and feeds this information back to a control circuit. The control circuit adjusts the operating conditions (such as drive voltage or temperature) of the MEMS resonator to compensate for frequency deviations, thereby maintaining stable frequency output despite temperature changes and mechanical property variations.
Solution Approach 2:
The patent changes the operating parameters of the MEMS resonator dynamically. By adjusting parameters such as drive voltage, bias conditions, or temperature based on detected frequency deviations, the system compensates for the inherent frequency instability caused by thermal expansion and elastic modulus changes, enabling MEMS resonators to maintain frequency stability comparable to crystal resonators.
2Reliability
If crystal resonators are used to achieve stable frequency, then frequency stability is improved, but device size increases and manufacturing cost rises
Solution Approach 1:
The patent creates a functional copy of the crystal resonator's frequency stability using MEMS technology. Instead of directly using crystal resonators, the system uses a MEMS resonator with similar resonant characteristics and applies electronic compensation to replicate the frequency stability function, thereby achieving the same performance with smaller size and lower cost.
Solution Approach 2:
The patent replaces the mechanical frequency stabilization mechanism inherent in crystal resonators (based on their stable piezoelectric properties and resonant modes) with an electronic control system. The electronic feedback loop substitutes for the passive mechanical stability of crystals, actively maintaining frequency while allowing the use of smaller, more integrable MEMS structures.
3Reliability
If temperature compensation is implemented for MEMS resonators, then frequency stability is improved, but device complexity increases
Solution Approach 1:
The patent merges the frequency detection function and temperature compensation control into an integrated control circuit that works seamlessly with the MEMS resonator. The control circuit combines frequency detection, temperature sensing, and actuation control into a unified system, reducing the number of separate components and simplifying the overall device architecture while achieving effective frequency stabilization.
Solution Approach 2:
The patent implements a self-regulating system where the MEMS resonator's own frequency output serves as the reference for detection. The frequency detector monitors the resonator's output and the control circuit automatically adjusts the resonator's operating conditions based on this feedback, enabling the system to self-correct frequency deviations without requiring complex external compensation mechanisms.
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 synthesizer effectively outputs a signal with stable frequency even when using MEMS resonators with large oscillation frequency fluctuations, enabling reliable operation in temperature-sensitive applications by finely controlling the frequency divider ratios and using accurate temperature detection.
Implementation Method 1
a resonance frequency of a MEMS resonator, a device manufactured by the MEMS technology, depends on its dimensions (a thermal expansion coefficient) and an elastic modulus of the material
Implementation Method 2
the frequency of the oscillation of the MEMS resonator decreases when the material expands as the temperature rises
Implementation Method 3
voltage controlled oscillator (VCO) capable of changing an oscillation frequency
Implementation Method 4
comparator that outputs a signal according to a phase difference between the signals divided by frequency dividers
Implementation Method 5
lowpass filter (LPF) that integrates the signal output from comparator, and converts the signal into a voltage having a frequency close to that of a direct current
Implementation Method 6
frequency divider that frequency-divides an oscillation signal output from the VCO
Data Source
AI summary
A synthesizer includes a synthesizer unit for generating a local oscillation signal based on a reference oscillation signal output from a reference oscillation unit including a MEMS resonator, a frequency fluctuation detector for detecting a frequency fluctuation of the MEMS resonator, and a frequency adjuster for adjusting a frequency of the local oscillation signal based on the frequency fluctuation detected by the frequency fluctuation detector. This synthesizer can output a signal with a stable frequency, even when an MEMS resonator demonstrating a large fluctuation in an oscillation frequency to temperatures is used.