Oven-Controlled MEMS Oscillator Set-Point Calibration for Frequency Stability

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Solution Overview

Problem

Existing oven controlled crystal oscillators (OCXOs) are large, have long start-up times, high power consumption, and suffer from frequency instability due to temperature gradients, while MEMS oscillators lack accuracy without extensive physical trimming.

Innovation Solution

A small, rapidly heatable oven controlled MEMS oscillator with a calibration system that adjusts set-points to correct for manufacturing variations, using a control circuitry and temperature sensor to minimize frequency fluctuations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a quartz crystal is used in an OCXO to achieve high frequency stability, then the device size becomes large and manufacturing cost increases

Engineering Contradiction:

Improvefrequency stabilityVSAvoiddevice size

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The patent changes the resonator material from quartz crystal to MEMS resonator, fundamentally altering the physical parameters of the oscillation system. MEMS resonators operate at higher frequencies with smaller physical dimensions, enabling compact OCXO designs while maintaining frequency stability through temperature control

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional quartz crystal mechanical resonance system with a MEMS-based mechanical resonance system. The MEMS resonator uses microfabricated structures with different mechanical properties that can be integrated into smaller packages, substituting the large quartz crystal while achieving similar or better performance

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If the oven is heated to maintain constant temperature for frequency stability, then the start-up time becomes long due to thermal time constant

Engineering Contradiction:

Improvefrequency stabilityVSAvoidstart-up time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent changes the thermal parameters of the oven system by using a MEMS resonator with smaller thermal mass compared to quartz crystals. The reduced size allows the oven to reach target temperature faster, decreasing the thermal time constant and enabling quicker start-up while maintaining the temperature control necessary for frequency stability

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the oven is heated to maintain constant temperature, then power consumption increases

Engineering Contradiction:

Improvefrequency stabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent changes the thermal and electrical parameters of the system by using a MEMS resonator instead of a quartz crystal. The smaller size and different material properties result in lower power requirements for the heating element and temperature control circuitry, reducing overall power consumption while maintaining the temperature control necessary for frequency stability

Inventive Principle:

Principle #35Parameter changes

4Volume of moving object

If MEMS processes are used to create small resonators, then manufacturing precision is insufficient without extensive physical trimming

Engineering Contradiction:

Improveresonator sizeVSAvoidfrequency accuracy

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The patent replaces the need for mechanical physical trimming with an electrical calibration system. The microcontroller adjusts the set-point temperature based on measured oscillation frequencies, providing post-manufacturing frequency adjustment without requiring mechanical intervention, thus maintaining manufacturing precision while keeping the device small

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 solution provides a compact, low-power MEMS oscillator with rapid start-up and improved frequency stability, capable of achieving high accuracy clocks by calibrating set-points to minimize oscillation frequency variations.

Implementation Method 1

a heater configured to heat the MEMS resonator to a set-point temperature that minimizes oscillation frequency variations of the MEMS resonator

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

changes in temperature causes the quartz crystal to expand or contract due to thermal expansion

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10425084B2Oven controlled MEMS oscillator and system and method for calibrating the same

Publication Date: 2019.09.24 MURATA MFG CO LTD

AI summary

A calibration system is provided for an oven controlled MEMS oscillator. The calibration system includes control circuitry that to separately selects predetermined target set-point values and controls a heater inside the oven controlled MEMS oscillator based on each of the selected target set-point values to adjust a set-point of the oven controlled MEMS oscillator. The system further includes an oscillation measurement circuit that measures respective oscillation frequencies at each adjusted set-point corresponding to each of the selected predetermined target set-point values. The measured oscillation frequencies can then be used to determine a target set-point operation value for the oven controlled MEMS oscillator, which can be sued to calibrate the oven controlled MEMS oscillator.