MEMS-Calibrated Clock Circuit for Stable Low-Power Oscillation
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Solution Overview
Problem
Existing clock signal oscillators, such as crystal oscillators, face integration challenges due to bulkiness and cost, while resistor-capacitor (R-C) oscillators suffer from stability issues, high Allan deviation, high temperature coefficient of frequency, and random telegraph noise.
Innovation Solution
A clock circuit incorporating a voltage-controlled oscillator (VCO) with a frequency-locked loop (FLL) and a microelectromechanical system (MEMS) resonator-based oscillator, where the MEMS resonator is used for calibration to maintain frequency stability, leveraging a multiplexer to switch between VCO and MEMS oscillator outputs based on calibration needs, and employing switched-capacitor resistors to reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a crystal oscillator is used, then frequency stability and accuracy are improved, but device size, cost, and integration difficulty increase
Solution Approach 1:
The system separates the oscillator function into two parts: a compact VCO for normal operation and a MEMS resonator for calibration. This segmentation allows the bulk crystal oscillator to be replaced with smaller components while maintaining stability through periodic calibration by the MEMS device.
Solution Approach 2:
The MEMS resonator acts as an intermediary calibration reference to adjust and stabilize the VCO's frequency output. Instead of directly using a large crystal oscillator, the system uses the MEMS device as a mediator to periodically correct the VCO, achieving crystal-level stability with smaller components.
2Volume of moving object
If an R-C oscillator is used for integration, then device size and cost are reduced, but frequency stability and noise performance deteriorate
Solution Approach 1:
The system implements a feedback mechanism where the MEMS resonator periodically measures the VCO's frequency accuracy and provides correction information. This feedback loop compensates for the VCO's inherent instability and noise, maintaining high frequency stability despite using a compact oscillator design.
Solution Approach 2:
The system dynamically adjusts the VCO's operating parameters based on calibration data from the MEMS resonator. By changing the control voltage or frequency parameters according to measured deviations, the system maintains accurate frequency output despite using a smaller, more integrable oscillator architecture.
3Use of energy by moving object
If a VCO with FLL is used for low power consumption, then energy efficiency is improved, but frequency accuracy and stability without calibration deteriorate
Solution Approach 1:
The system uses periodic calibration action where the MEMS resonator intermittently measures and corrects the VCO's frequency rather than continuously operating. This periodic intervention maintains frequency accuracy while allowing the low-power VCO to operate between calibration cycles, achieving both energy efficiency and precision.
Data Source
AI summary
A clock circuit includes a voltage-controlled oscillator (VCO) having a control input and a first clock output. The clock circuit includes a frequency-locked loop (FLL) having an FLL input and a control output, the control output coupled to the control input. A microelectromechanical system (MEMS) resonator-based oscillator has a second clock output. A multiplexer has a first multiplexer input, a second multiplexer input, a selection input, and a multiplexer output. The first multiplexer input is coupled to the first clock output. The second multiplexer input is coupled to the second clock output. The multiplexer output is coupled to the FLL input.