MEMS Resonator Oscillator With Transformer Coupling for Low Phase Noise
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Solution Overview
Problem
Coupling a MEMS resonator to an oscillator circuit while maintaining sufficient phase noise, power consumption, and oscillation stability is challenging due to thermal noise, which is not eliminated by tuning circuit components, and increasing the amplitude of the oscillator signal to mitigate this noise results in decreased switching speed and increased capacitance, affecting impedance.
Innovation Solution
The implementation of an oscillator circuit inductively coupled to a MEMS resonator via a transformer, which cancels increased capacitance and reduces nonlinearities by using a control terminal coupling network to reduce voltage swings at the transistors' bases and a second terminal coupling network with a resonant frequency matching the MEMS resonator, thereby stabilizing the oscillator circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the amplitude of the oscillator signal is increased to mitigate thermal noise, then the thermal noise is reduced, but the switching speed decreases and capacitance increases
Solution Approach 1:
The patent introduces a transformer as an intermediary component between the oscillator circuit and the MEMS resonator. The transformer enables inductive coupling that allows the oscillator to operate at lower amplitudes while still effectively driving the resonator, thus mitigating thermal noise without sacrificing switching speed or increasing capacitance
Solution Approach 2:
The patent changes the coupling mechanism from direct capacitive coupling to inductive coupling through a transformer. This parameter change in the coupling method allows for optimized operating conditions where the oscillator can maintain low amplitude operation, reducing thermal noise impact while preserving fast switching performance
2Object-affected harmful factors
If the amplitude of the oscillator signal is increased to mitigate thermal noise, then the thermal noise is reduced, but the impedance increases
Solution Approach 1:
The transformer acts as an impedance-matching intermediary between the oscillator circuit and the MEMS resonator. By using inductive coupling, the transformer allows the oscillator to operate at lower amplitudes with reduced impedance while still effectively driving the resonator, thus reducing thermal noise without the harmful side effect of increased impedance
Solution Approach 2:
The patent changes the coupling topology to inductive coupling, which fundamentally alters the impedance characteristics of the circuit. This parameter change enables the oscillator to operate with lower amplitude and reduced impedance while maintaining effective resonator drive, thereby reducing thermal noise impact
3Measurement precision
If circuit components are tuned to reduce nonlinearities, then phase noise is reduced, but thermal noise remains unaffected
Solution Approach 1:
The transformer introduces inductive coupling as an intermediary mechanism that fundamentally changes how the oscillator interacts with the resonator. This allows for reduced oscillator amplitude operation, which directly addresses thermal noise reduction while the tuned circuit components continue to handle phase noise, achieving both goals simultaneously
Solution Approach 2:
The patent changes the operating parameters of the oscillator by introducing inductive coupling, enabling operation at lower amplitudes. This parameter change directly reduces thermal noise impact while the tuned circuit components maintain their function of reducing phase noise through nonlinearity management
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 approach effectively reduces thermal noise, maintains low phase noise, and enhances oscillation stability by canceling increased capacitance and reducing nonlinearities, while allowing for higher voltage swings without degrading switching speed or increasing impedance.
Implementation Method 1
a resonator coupling network configured to inductively couple MEMS resonator terminals to the first and third current terminals
Implementation Method 2
A second terminal coupling network resonant frequency is approximately that of MEMS resonator
Data Source
AI summary
A device includes a MEMS resonator and oscillator circuit coupled to the MEMS resonator. The circuit includes a first transistor having a first control terminal and first and second current terminals, and a second transistor having a second control terminal and third and fourth current terminals. The circuit includes a resonator coupling network configured to inductively couple MEMS resonator terminals to the first and third current terminals, and to couple the first and third current terminals. The circuit includes a control terminal coupling network configured to couple the first and second control terminals, and to reduce a voltage swing at the first and second control terminals relative to a voltage swing at the first and third current terminals. The circuit includes a second terminal coupling network configured to couple the second and fourth current terminals. A second terminal coupling network resonant frequency is approximately that of MEMS resonator.