Crystal Oscillation Circuit Filtering for Low Phase Noise
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Solution Overview
Problem
The crystal oscillation circuit faces challenges in reducing phase noise due to sensitivity to waveform fluctuations, which is exacerbated by the need for small transistors at the input stage of the Schmitt trigger circuit, leading to increased phase noise in the clock signal output.
Innovation Solution
Incorporating a bandpass filter with a predetermined passband that includes the oscillation frequency, connected to a second inverter circuit sharing the input with the first inverter circuit, which is connected in parallel to the crystal vibrating element, replaces the Schmitt trigger circuit to reduce phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the size of the transistor at the input stage of the Schmitt trigger circuit is made small to reduce load, then the load at the crystal vibrating element output side is reduced, but the phase noise of the clock signal becomes large due to sensitivity to waveform fluctuations
Solution Approach 1:
A wave filter is introduced as an intermediary component between the inverter circuit and the Schmitt trigger circuit. This filter acts as a mediator that conditions the oscillation signal before it reaches the Schmitt trigger, removing high-frequency noise components that would otherwise be amplified by the small transistor, thus reducing phase noise while maintaining low load on the crystal vibrating element
Solution Approach 2:
The wave filter performs preliminary cleaning of the oscillation signal by removing high-frequency noise components before the signal is processed by the Schmitt trigger circuit. This preliminary action prevents the noise from affecting the clock signal generation, allowing the use of small transistors without incurring phase noise penalties
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 effectively reduces phase noise by filtering out high-frequency noise at startup, allowing for a more stable and accurate clock signal output with reduced sensitivity to environmental variations and manufacturing dispersion.
Implementation Method 1
a wave filter connected to the second inverter circuit and having a passband that is determined in advance and includes an oscillation frequency of the oscillation signal
Implementation Method 2
An oscillation circuit that includes a crystal vibrating element and an inverter circuit
Data Source
AI summary
A semiconductor device including a first inverter circuit connected in parallel to a crystal vibrating element; a second inverter circuit connected to the first inverter circuit so as to share an input therewith, and outputting an oscillation signal; and a wave filter connected to the second inverter circuit and having a passband that is determined in advance and includes an oscillation frequency of the oscillation signal.