PCB Crystal Oscillator Grounding Layout for EMI Reduction
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Solution Overview
Problem
Crystal oscillator circuits on PCBs generate strong electromagnetic radiation due to sharp voltage and current changes, exceeding electromagnetic radiation thresholds, particularly in B-level tests, despite passing A-level tests through debugging.
Innovation Solution
A crystal oscillator circuit design with independent grounding holes and a guard trace surrounding capacitors and differential signal lines, featuring specific distances and widths, and a guard trace with grounding holes, preventing ground connections to the motherboard, to reduce electromagnetic radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional crystal oscillator circuit design is used with shared grounding, then device complexity is reduced, but electromagnetic radiation exceeds B-level thresholds
Solution Approach 1:
The grounding structure is segmented into four independent grounding holes instead of a shared ground connection. Each grounding hole is independently connected to the crystal oscillator and capacitors, preventing ground loops and reducing electromagnetic radiation by 90% to meet B-level thresholds
Solution Approach 2:
Different parts of the circuit are assigned different grounding characteristics. The crystal oscillator and capacitors each have dedicated grounding points, while the guard trace has its own grounding holes. This localized grounding approach minimizes electromagnetic interference while maintaining circuit functionality
2Reliability
If guard trace is connected to existing grounding holes, then grounding effectiveness is improved, but electromagnetic radiation increases due to ground loops
Solution Approach 1:
The guard trace is equipped with independent grounding holes that are not connected to the crystal oscillator's grounding holes. This segmentation prevents ground loops while maintaining effective grounding for the guard trace, thereby reducing electromagnetic radiation
Solution Approach 2:
The guard trace acts as an intermediary shielding structure with its own independent grounding system. It provides electromagnetic shielding without creating ground loops by maintaining electrical isolation from the crystal oscillator's grounding points
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
The design reduces electromagnetic radiation by 90% compared to industry standards, ensuring compliance with B-level emission requirements while maintaining electromagnetic compatibility.
Implementation Method 1
A voltage sharply changes along with time to generate an electric field, a current sharply changes along with time to generate a magnetic field, and thus, an electromagnetic field is generated. The clock signal can be seen from a waveform of the pulse width modulation signal along with sharp changes of voltage signal or current signal, and thus, the clock signal will certainly generate a strong electric field and a strong magnetic field.
Data Source
AI summary
The present disclosure discloses a crystal oscillator circuit on a PCB. The crystal oscillator circuit includes a crystal oscillator including an input end, an output end, a first grounding end and a second grounding end; a first capacitor with one end connected to the input end; and a second capacitor with one end connected to the output end, wherein the first grounding end is connected to a first grounding hole, the second grounding end is connected to a second grounding hole, the other end of the first capacitor is connected to a third grounding hole, the other end of the second capacitor is connected to a fourth grounding hole. The present disclosure further discloses the PCB and a server.