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PCB manufacturer:Annular Rings in High-Speed Circuits

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Popularity:669Dated :06-09-2022 12:12【big well Small

As PCB manufacturer knows that,the annular rings in a via create a parallel plate capacitor, which affects the via impedance. This implies that more rings along the via barrel, either functional or non-functional, raise the parasitic capacitance of the via. Furthermore, this will decrease the via’s impedance and move it closer to the trace impedance. Therefore, you should carry out impedance matching on primary traces and components.

Any non-functioning stub available at the via end contains a set of resonance frequencies as high-speed digital signals and high-frequency AC signals spread through the via. Since more non-functional pads along the via barrel raise the PCB capacitance, they reduce the quarter wavelength resonance frequency of the via stub. This further intensifies the via insertion loss and lowers the signal quality.

The best strategy of preventing via stub resonance is back-drilling the stub to achieve the smallest size. You can then set the lowest order resonance frequency of the via stub higher than the signal working frequency. This will subdue the via stub resonance. Non-functional pads along the barrel minimize the lowest order resonance frequency and eliminate the standard method used to prevent insertion loss issues.

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