Crystal Oscillator Supply Buffering for Low Noise Stability

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Solution Overview

Problem

Conventional crystal oscillators face the challenge of providing noise immunity against power supply noise while minimizing the introduction of additional circuit noise.

Innovation Solution

A crystal oscillator design incorporating a voltage regulator, source follower, shunt capacitors, and a clocked lowpass filter to regulate power supply voltage, using a source follower to convert voltage and shunt capacitors to ground nodes, and a clocked lowpass filter to filter reference voltage, reducing noise through synchronized pulsing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a voltage regulator is used to provide noise immunity against power supply noise, then noise immunity is improved, but circuit noise is introduced

Engineering Contradiction:

Improvenoise immunityVSAvoidcircuit noise

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

A source follower circuit is introduced as an intermediary between the voltage regulator and the oscillating circuit. The source follower acts as a buffer that isolates the oscillating circuit from noise generated by the voltage regulator, while still providing regulated voltage. This intermediary element transfers the beneficial voltage regulation function while blocking the harmful noise transmission path.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The voltage regulator continuously provides regulated voltage to the source follower, which in turn continuously supplies stable voltage to the oscillating circuit. This continuous regulated supply maintains stable oscillation while the source follower's high input impedance prevents loading effects and noise coupling from the regulator stage.

Inventive Principle:

Principle #20Continuity of useful action

2Stability of the object's composition

If a voltage regulator is used to establish stable supply voltage, then voltage stability is improved, but the regulator itself becomes a noise source

Engineering Contradiction:

Improvevoltage stabilityVSAvoidregulator noise

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The source follower serves as a mediator that decouples the noise-generating voltage regulator from the noise-sensitive oscillating circuit. It maintains the voltage stability benefit while preventing the regulator's inherent noise from reaching the oscillator, effectively filtering the regulator's output before it reaches the sensitive circuitry.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The source follower is designed with simple transistor-based circuitry that is low-cost and easy to implement. It provides effective noise isolation without requiring complex or expensive filtering components, making it an economical solution for eliminating regulator noise while maintaining voltage stability.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

Effectively suppresses both power supply noise and circuit noise, maintaining stable oscillation with minimal disturbance, enhancing noise immunity and reducing overall circuit noise.

Implementation Method 1

a crystal placed across the first node and a second node

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a first shunt capacitor configured to shunt the first node to ground; a second shunt capacitor configured to shunt the second node to ground

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 3

a clocked lowpass filter configured to receive a reference voltage and output the control voltage in accordance with the pulsed signal

Methodology Applied

Scientific EffectLowpass filtering: Filter (electronic)

Data Source

PatentUS12418262B2Low noise crystal oscillator

Publication Date: 2025.09.16 REALTEK SEMICON CORP

AI summary

A crystal oscillator having a voltage regulator configured to receive a first power supply voltage and output a second power supply voltage; a source follower configured to receive the second power supply voltage and output a third power supply voltage in accordance with a control voltage; a first inverter operating under the third power supply voltage and configured to receive a first oscillatory signal from a first node and output a second oscillatory signal at a second node; a second inverter operating under the third power supply voltage and configured to output a third oscillatory signal; a crystal placed across the first node and a second node; a first shunt capacitor configured to shunt the first node to ground; a second shunt capacitor configured to shunt the second node to ground; and a clocked lowpass filter configured to output the control voltage in accordance with the pulsed signal.