PCB Band Elimination Filter Using Grounded Open Stubs
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Solution Overview
Problem
Existing band elimination filters with open stubs of specific electrical lengths suffer from increased electrical coupling and resonance frequency shifts, leading to ineffective attenuation of unwanted frequencies, resulting in a larger occupation area on printed wiring boards and inadequate suppression of electromagnetic interference (EMI).
Innovation Solution
A printed circuit board design incorporating a distributed constant circuit with a main wiring pattern and two open-ended wiring patterns, where one pattern is grounded and the other extends in the same direction, allowing for controlled electrical coupling and attenuation of frequencies, thereby reducing EMI while minimizing the board's size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If two open stubs are disposed close to each other to reduce occupation area, then the filter size is reduced, but electrical coupling between stubs increases causing resonance frequency shifts and ineffective attenuation
Solution Approach 1:
A ground wiring pattern is introduced as an intermediary element between the two open stubs. This ground pattern acts as a mediator that electrically isolates the stubs from each other, preventing harmful electrical coupling and resonance frequency shifts while allowing the stubs to be positioned close together for compact filter design.
Solution Approach 2:
The filter structure is segmented into three distinct components: two open stubs for frequency attenuation and a ground wiring pattern for electrical isolation. This segmentation allows each component to perform its specific function independently while working together as an integrated compact filter system.
2Reliability
If open stubs are disposed far apart to eliminate coupling effects, then attenuation effectiveness is improved, but occupation area of the filter increases
Solution Approach 1:
The ground wiring pattern serves as a compact intermediary that enables close positioning of stubs without suffering from coupling effects. This mediator allows the system to achieve the electrical isolation equivalent of large spacing while maintaining physical compactness.
Solution Approach 2:
The solution transitions from horizontal spacing (one dimension) to vertical layering with ground patterns (multiple dimensions). By utilizing the ground layer beneath the signal layer, the filter achieves isolation without increasing the horizontal occupation area, effectively using another dimension to resolve the contradiction.
3Ease of manufacture
If lumped parameter elements are used in band elimination filters, then filter design is simplified, but achieving desired cutoff frequency in GHz band becomes difficult due to small component values
Solution Approach 1:
The patent replaces lumped parameter elements (mechanical/circuit components) with distributed constant circuit elements (wiring patterns on PCB). This substitution eliminates the need for precision small-value components while achieving the same frequency attenuation function through the geometric dimensions of the wiring patterns, which can be manufactured with standard PCB tolerances.
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 effectively attenuates signal components at integral multiples of the fundamental frequency, suppressing EMI while maintaining a compact board size by optimizing the electrical lengths and positions of the wiring patterns, thereby enhancing noise reduction and reducing the board's occupation area.
Implementation Method 1
an open stub having an electrical length of 1/4 wavelength relative to a fundamental frequency is connected to a line (power supply line) connected to an LSI serving as a noise source so as to attenuate noise of frequencies of odd multiples of the fundamental frequency
Implementation Method 2
as a gap between the stubs becomes small, electric coupling between the stubs is increased
Data Source
AI summary
A printed circuit board includes a printed wiring board and a transmission circuit implemented on the printed wiring board and transmitting digital signals. The printed wiring board connected to the transmission circuit includes a main wiring pattern transmitting digital signals and a first wiring pattern having a connection end connected to the main wiring pattern and an open end. The printed wiring board further includes a second wiring pattern having a grounded end and an open end and extending in a direction in which the first wiring pattern extends. The second wiring pattern is disposed such that the grounded end of the second wiring pattern is disposed adjacent to the connection end or the open end of the first wiring pattern. By this, a printed circuit board capable of suppressing EMI is provided while increase in size of the printed wiring board is avoided.