Single-Oscillator Frequency-Control Circuit for Temperature-Stable Clocks
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Solution Overview
Problem
MEMS resonators face challenges in temperature stability and initial accuracy, with uncompensated MEMS resonators having a high temperature coefficient compared to quartz oscillators, and conventional methods like electrostatic pulling are ineffective for high-frequency MEMS oscillators.
Innovation Solution
A frequency-control circuit that alters pulses of input signals from oscillators to tune the output frequency to a desired target frequency, using techniques such as pulse removal, addition, or switching between oscillators, coupled with temperature compensation to achieve precise and stable clock signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electrostatic pulling is used to tune MEMS oscillators, then frequency adjustment is achieved, but the method is ineffective for high-frequency MEMS oscillators due to very high equivalent stiffness
Solution Approach 1:
The patent replaces the mechanical electrostatic pulling method with a signal processing approach. Instead of physically adjusting the resonator frequency through electrostatic forces, the invention uses pulse altering circuits to modify the output signal frequency based on the resonator's natural oscillations, effectively decoupling frequency tuning from mechanical adjustment.
Solution Approach 2:
The patent introduces pulse altering circuits as an intermediary between the MEMS resonator and the output frequency signal. These circuits count resonator oscillations and generate output pulses based on predetermined counts, acting as a mediator that transforms the resonator's high-frequency oscillations into a usable lower frequency output without requiring direct mechanical tuning of the resonator.
2Device complexity
If uncompensated MEMS resonators are used, then device size and cost are reduced, but temperature stability deteriorates with a temperature coefficient of approximately 40 ppm/°C
Solution Approach 1:
The patent implements feedback through temperature sensing and compensation circuits. A temperature sensor monitors the operating temperature, and this information is fed back to the pulse altering circuit, which adjusts the pulse count accordingly to compensate for temperature-induced frequency drift, maintaining stable output frequency despite temperature variations.
Solution Approach 2:
The patent changes the operational parameters of the pulse altering circuit based on temperature conditions. By adjusting the predetermined pulse count parameter in response to temperature changes, the system compensates for the resonator's temperature coefficient without requiring physical or structural modifications to the resonator itself.
3Reliability
If quartz oscillators are used instead of MEMS resonators, then temperature stability and initial accuracy are improved, but device size and cost increase
Solution Approach 1:
The patent creates a functional copy of the quartz oscillator's temperature compensation capability using digital signal processing. Instead of relying on the physical properties of quartz crystal, the invention uses pulse counting and altering circuits to replicate the frequency stability function, achieving similar reliability with MEMS technology.
Solution Approach 2:
The patent substitutes the mechanical quartz crystal resonator system with an electronic pulse altering system. By replacing the physical quartz oscillator with a MEMS resonator plus digital pulse processing circuitry, the invention achieves comparable or superior performance while reducing device complexity and cost.
4Measurement precision
If pulse altering techniques are applied to tune output frequency, then tuning resolution is enhanced and spurious signals are reduced, but circuit complexity increases
Solution Approach 1:
The patent segments the frequency control function into distinct modular components: a pulse counter that counts resonator oscillations, a pulse altering circuit that modifies the pulse train based on predetermined counts, and a temperature compensation module. This segmentation allows each component to perform a specific function with high precision while maintaining overall system manageability.
Solution Approach 2:
The pulse altering circuit operates autonomously based on predetermined pulse counts stored in memory or registers. The system self-adjusts the output frequency by automatically altering pulses according to the counted resonator oscillations, reducing the need for complex external control mechanisms and simplifying the overall circuit architecture.
Data Source
AI summary
A frequency-control circuit, which is configured to receive a first signal having a first untuned frequency from a first oscillator, and to alter one or more pulses of the first signal to tune an output frequency of an output clock signal to have an average frequency at the desired target frequency. In some embodiments, the frequency-control circuit receives a signal from a single oscillator to generate a calibrated, precise, and temperature-stable clock.