Parallel Quarter-Wavelength Line Filter for High-Speed Digital EMI
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Solution Overview
Problem
Conventional band-elimination filters struggle to effectively attenuate frequencies that are even multiples of the basic frequency in high-speed digital signal transmission, leading to strong electromagnetic interference (EMI) in domains where no spectrum of the transmitted signal is present.
Innovation Solution
A printed circuit board design incorporating ¼ wavelength lines with specific termination configurations, including one line with one end open and the other end grounded, and another with both ends open, arranged in parallel to the transmission line, to attenuate frequencies that are integral multiples of the basic frequency, thereby reducing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional band-elimination filter using lumped elements (chip parts) is used, then the filter structure is simple and easy to manufacture, but it cannot provide desired frequency filter-out in high-frequency domains (GHz band) due to small constant values and variation in element values
Solution Approach 1:
The patent replaces the conventional lumped element mechanical structure (chip parts with fixed inductance and capacitance values) with a distributed element transmission line structure. The transmission line's physical dimensions (length, width, thickness) replace the discrete component values, providing stable frequency filtering characteristics in the GHz band without suffering from component value variations.
2Productivity
If transmission speed is increased to transmit large-volume data at high speed, then productivity improves, but signal timing differences due to skew increase and EMI becomes more significant
Solution Approach 1:
The patent converts the harmful EMI radiation at integral multiple frequencies into a beneficial filtering opportunity. By identifying that EMI occurs specifically at frequencies where the transmitted signal has no spectrum (integral multiples of the one-bit cycle frequency), the patent places band-elimination filters at these exact frequencies, transforming the harmful radiation pattern into a predictable and filterable characteristic.
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 achieves significant attenuation of both odd and even multiple frequency components, effectively mitigating EMI across the entire frequency spectrum, ensuring reliable high-speed digital signal transmission.
Implementation Method 1
a first 1/4 wavelength line arranged on the substrate in parallel to the transmission line, wherein the first 1/4 wavelength line has one end opened and the other end connected to grounded, and a length of the first 1/4 wavelength line in a direction parallel to the transmission line is set as 1/4 of a wavelength of a basic frequency
Implementation Method 2
a second 1/4 wavelength line arranged on the substrate in parallel to the transmission line, wherein the second 1/4 wavelength line has both ends opened, and a length of the second 1/4 wavelength line in a direction parallel to the transmission line is set as 1/4 of a wavelength of the basic frequency
Data Source
AI summary
Provided is a printed circuit board configured to remove undesired signals generated in a transmission line, the signals having frequencies that are integral multiples of a basic frequency. Two ¼ wavelength lines 5 and 6 each having a length that is ¼ of a basic frequency corresponding to a data rate of coded digital signal are arranged at a signal wiring layer, which is one of surface layers of a substrate 8, along a transmission line 3 for transmitting the digital signal. One end 15a of the first ¼ wavelength line 5 is opened, and another end 15b is grounded to a ground 7. Both ends 16a and 16b of the second ¼ wavelength line 6 are opened.