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FAQs
What are some design considerations for base board budget?
- As the PCB temperature rises, the insertion loss (IL) of the PCB trace becomes higher
- Process fluctuation during PCB manufacturing can result in slightly narrower or wider line widths, which can lead to fluctuations in IL
- The amplitude of the Nyquist frequency signal (16-GHz sine wave in the case of 32 GT/s NRZ signaling) at the source side is 800 mV pk-pk, which will reduce to about 12.7 mV after 36 dB of attenuation. This underscores the need to leave some IL margin for the receiver to account for reflections, crosstalk, and power supply noise that all potentially will degrade the SNR.
Thus, the IL budget reserved for the PCB trace on the system base board should be 16 dB minus some amount of margin, which is reserved for the above factors. Many hardware engineers and system designers tend to leave 10-20% of the overall channel IL budget as margin for such factors. In the case of a 36-dB budget, this amounts to 4-7 dB.