PCB Channel Optimization Techniques for High-Speed Differential Interconnects

Chew, Li Wern; Tan, Cheng; Chai, Ming Dak; Lim, Yun Rou

doi:10.23919/icep55381.2022.9795393

Cited by 3 publications

(1 citation statement)

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“…In the scientific literature, there are a number of studies that investigate the influence of AC coupling SMT capacitor pads and cutouts under them on the change of impedance of the differential line [7], [8], [9]. These studies address ways of improving high-speed interconnects [7], analyze improvements of the digital signal eyediagram when cut-out compensation is employed [8] and also how the shape of the cut-outs affects the impedance [9]. There are also research papers that investigate the effect of cut-out shape on impedance compensation specifically for 0201 size SMT components [10].…”

Section: Introductionmentioning

confidence: 99%

Analysis of SMT component land pad discontinuity effect on the overall transmission line impedance in high-speed applications

Barzdėnas

Vasjanov

2023

Journal of Electrical Engineering

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High-speed and high-frequency PCB interconnect solutions with the slightest discontinuities in the physical geometry along the microstrip transmission line can significantly degrade the integrity of the signal being transferred. This paper presents an analysis of SMT component pads and their impact on the successive transmission line impedance. During 0805, 1206 and 2512 package size SMT component pad discontinuity evaluations it was spotted, that the increasing deviation from target impedance affects the microstrip impedance segment following the discontinuity. A 25 Ω impedance offset at the SMT pad reduces the line impedance afterwards by up to 7 Ω. A 37 Ω impedance offset results in a microstrip impedance reduction by up to 15 Ω, whereas a 45 Ω impedance change leads to a reduction of successive segment impedance by up to 30 Ω. This effect is also present in multiple evenly-spaced discontinuities. But a single reference plane cut-out, which is twice as wide as the SMT component discontinuity, substantially improves the overall impedance of the transmission line, including the successive line segment impedance drop.

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