PCB Shield Trap Filter for High-Frequency Noise Suppression
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Solution Overview
Problem
Conventional technologies fail to effectively reduce unintentional electromagnetic waves emitted by optical transmission devices, particularly at high frequencies above 20 GHz, due to limitations in impedance reduction and loop current-induced radiation.
Innovation Solution
A printed circuit board design incorporating a shield with trap filters in the power supply wiring, featuring resonance circuits and strategically placed via holes, effectively attenuates switching noise across a wide frequency range, including frequencies above 20 GHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If two chip capacitors are arranged with appropriate intervals between power supply terminal and power supply circuit, then unintentional electromagnetic wave radiation is reduced in frequency range of 30 MHz to 1 GHz, but high-frequency noise component above 20 GHz cannot be sufficiently reduced
Solution Approach 1:
The patent changes the electrical parameters of the power supply wiring by introducing trap filters with specific resonance frequencies matched to the clock signal frequency. This transforms the wiring from a simple conductor into a frequency-selective structure that presents high impedance at specific frequencies, thereby suppressing high-frequency noise while maintaining low-frequency power delivery.
Solution Approach 2:
The trap filter acts as an intermediary element inserted into the power supply wiring. It mediates between the power source and the IC by selectively blocking high-frequency noise components while allowing low-frequency power signals to pass through, thus protecting the IC from high-frequency electromagnetic radiation.
2Object-affected harmful factors
If series inductance of chip capacitors is reduced to lower impedance, then decoupling effectiveness is improved, but loop current still generates large amount of unintentional electromagnetic radiation
Solution Approach 1:
The patent extracts the noise suppression function from the decoupling capacitors and implements it separately through trap filters in the power supply wiring. This separation allows the capacitors to focus on low-frequency decoupling while the trap filters handle high-frequency noise, preventing loop current radiation without increasing overall circuit complexity.
Solution Approach 2:
The power supply system is segmented into different frequency handling zones: decoupling capacitors handle low-frequency power delivery and decoupling, while trap filters handle high-frequency noise suppression. This segmentation allows each component to optimize its function without compromising the other, effectively reducing electromagnetic radiation.
3Productivity
If clock signal frequency is increased to achieve high bit rate transmission, then transmission speed is improved, but unintentional electromagnetic wave radiation increases significantly
Solution Approach 1:
The patent applies preliminary anti-action by placing trap filters in advance within the power supply wiring to counteract the high-frequency noise generated by high-speed clock signals. The trap filters are designed with resonance frequencies matching the clock signal frequency, creating high impedance that blocks noise propagation before it can radiate from the IC, thus enabling high-bit-rate transmission without excessive electromagnetic radiation.
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 solution significantly reduces unintentional electromagnetic wave radiation, achieving up to 28 dB reduction in maximum electric field intensity across a 4.3 GHz bandwidth, thereby improving noise suppression and compatibility with high-frequency optical transmission systems.
Implementation Method 1
a trap filter provided to the power supply wiring, for attenuating a frequency component corresponding to a frequency of the clock signal
Implementation Method 2
a shield for covering the signal output circuit
Data Source
AI summary
A printed circuit board includes a substrate, a signal output circuit formed on the substrate for outputting a clock signal, a shield for covering the signal output circuit, a power supply wiring for connecting the signal output circuit and a power source, and a trap filter provided to the power supply wiring and provided inside the shield, for attenuating a frequency component corresponding to a frequency of clock signal. The trap filter includes a resonance circuit having one portion of the power supply wiring, an inner-layer wiring of the substrate located below the one portion of the power supply wiring, an inner-layer ground wiring of the substrate located below the inner-layer wiring, and a via hole for connecting the one portion of the power supply wiring and the inner-layer wiring.