MEMS Oscillator Q-Factor Control for Fast Start-Up and Low Power
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Solution Overview
Problem
Conventional oscillators, such as quartz oscillators, are large and unsuitable for high integration with electronic circuitry, and MEMS resonators face challenges with frequency tuning and long start-up times, particularly requiring high DC voltages and taking milliseconds to initialize.
Innovation Solution
The integration of a microelectromechanical-based oscillator circuit comprising a microelectromechanical resonator, a variable impedance circuit, and an adjustable gain amplifier, with a Q-factor control circuit that adjusts impedance and gain during start-up and post-start-up intervals to reduce power consumption and enhance frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If active frequency tuning techniques are used to tune MEMS resonators, then frequency tuning capability is achieved, but relatively large DC voltages are required which are incompatible with low operating voltages of conventional oscillator circuits
Solution Approach 1:
The patent changes the tuning parameter from DC voltage to a different electrical parameter that can be controlled at low voltages. The adjustable gain amplifier modifies the electrical characteristics of the resonator circuit without requiring high voltage, thereby achieving frequency tuning while maintaining compatibility with low-voltage oscillator circuits.
Solution Approach 2:
The patent replaces the mechanical/electrical high-voltage tuning mechanism with an electronic control mechanism using an adjustable gain amplifier. This substitution allows frequency tuning to be achieved through electronic gain adjustment rather than through high-voltage electrical actuation of the piezoelectric layer.
2Ease of manufacture
If MEMS resonators are used to create integrated silicon oscillators, then small form factor and ease of integration are achieved, but start-up times are relatively long on the order of milliseconds
Solution Approach 1:
The patent applies preliminary action by pre-biasing the resonator or pre-charging energy storage elements in the oscillator circuit before正式 operation begins. This preliminary energy input reduces the time required for the oscillator to reach its steady-state oscillation, thereby reducing start-up time from milliseconds to microseconds while maintaining integration benefits.
Solution Approach 2:
The patent uses feedback mechanisms where the output of the oscillator is fed back to the adjustable gain amplifier, which continuously adjusts the gain to maintain oscillation. This feedback control accelerates the start-up process by providing positive reinforcement during the initialization phase, allowing the system to quickly establish and maintain oscillation.
3Reliability
If high gain is used in the amplifier to ensure oscillation start-up, then oscillation reliability is improved, but power consumption increases
Solution Approach 1:
The patent applies dynamics by making the amplifier gain variable rather than fixed. The adjustable gain amplifier dynamically adjusts its gain based on the oscillation state: using high gain during start-up to ensure reliable oscillation establishment, then automatically reducing gain once oscillation is established to minimize power consumption. This dynamic adaptation resolves the contradiction between reliability and power consumption.
Solution Approach 2:
The patent employs periodic action through automatic gain control that periodically adjusts the amplifier gain in response to oscillation amplitude. During start-up, the system operates with high gain; once oscillation amplitude reaches a threshold, the gain is periodically reduced and maintained at a lower level, creating a periodic control pattern that ensures reliable start-up while minimizing ongoing power consumption.
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
This configuration enables rapid start-up times in microseconds, reduces power consumption, and maintains high quality factor characteristics, making it suitable for compact and efficient integration with electronic circuitry.
Implementation Method 1
lateral-mode piezoelectric resonators, such as thin-film piezoelectric-on-silicon (TPoS) resonators
Implementation Method 2
a variable impedance circuit (e.g., varistor) and an adjustable gain amplifier
Implementation Method 3
an adjustable gain amplifier is electrically coupled to the variable impedance circuit
Data Source
AI summary
Oscillator circuits include a MEMs resonator, a variable impedance circuit (e.g., varistor) and an adjustable gain amplifier. The variable impedance circuit includes a first terminal electrically coupled to a first terminal of the MEMs resonator and the adjustable gain amplifier is electrically coupled to the variable impedance circuit. The adjustable gain amplifier may have an input terminal electrically coupled to the variable impedance circuit and a second terminal of the MEMs resonator may receive, as feedback, a signal derived from an output of the adjustable gain amplifier. A Q-factor control circuit may be provided, which is configured to drive the variable impedance circuit and the adjustable gain amplifier with first and second control signals, respectively, that cause an impedance of the variable impedance circuit and a gain of the adjustable gain amplifier to be relatively high during a start-up time interval and relatively low during a post start-up time interval.