Crystal Oscillator Bias Reset Circuit for Lower Phase Noise
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Solution Overview
Problem
Existing crystal oscillators face challenges in reducing phase noise of the reference clock without introducing side effects, which affects the overall performance of electronic systems.
Innovation Solution
A crystal oscillator design that incorporates a phase noise reduction circuit generating reset pulses to reset the bias voltage, thereby reducing noise introduced by the bias resistor without requiring calibration of the reset pulse timing, allowing for efficient phase noise reduction without additional complexity or costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional circuits are added to reduce phase noise of the crystal oscillator, then phase noise performance is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the bias resistor from the oscillator circuit entirely, replacing it with a transistor-based biasing scheme. This eliminates the noise source associated with the bias resistor while maintaining the necessary biasing function, thereby reducing phase noise without adding complex noise reduction circuits.
Solution Approach 2:
The patent introduces a current source as an intermediary element to provide bias current to the transistor, replacing the traditional bias resistor. This current source acts as a mediator that provides the necessary DC bias while introducing minimal noise, thus improving phase noise performance without requiring complex additional circuits.
2Ease of manufacture
If bias resistor is used to set operating point, then ease of manufacture is improved, but phase noise increases
Solution Approach 1:
The patent changes the fundamental parameter of biasing from resistor-based voltage division to transistor-based current control. By using the transistor's inherent characteristics and a simple current source, the circuit achieves both ease of manufacture and low phase noise, as the transistor naturally provides stable biasing with minimal noise contribution.
Solution Approach 2:
The patent replaces the bias resistor with a simple current source implementation that can be realized with basic transistor configurations. This substitution uses simpler, more noise-resistant components that are equally easy to manufacture but significantly reduce the harmful noise effects.
Data Source
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AI summary
A crystal oscillator and a phase noise reduction method thereof are provided. The crystal oscillator may include a crystal oscillator core circuit, a bias circuit coupled to an output terminal of the crystal oscillator core circuit, a pulse wave buffer coupled to the output terminal of the crystal oscillator core circuit, and a phase noise reduction circuit coupled to the output terminal of the crystal oscillator core circuit. The crystal oscillator core circuit may generate a sinusoidal wave. The bias circuit may provide a bias voltage of the sinusoidal wave. The pulse wave buffer may generate a pulse wave according to the sinusoidal wave. The phase noise reduction circuit may generate a reset signal including at least one reset pulse for resetting the bias voltage. In addition, the reset signal is generated without calibrating the at least one reset pulse to a zero-crossing point of the sinusoidal wave.