TMS320C6678: Value for series resistors (Ra) between LMK03318 LVPECL outputs and TMS320C6678 LJCB/CML clock inputs

Hello,

I originally posted this question on the Clock & Timing forum and was asked by Hao to re-post the question on this forum.

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1095662/lmk03318-value-for-series-resistors-between-lmk03318-lvpecl-outputs-and-tms320c6678-ljcb-cml-clock-inputs/4061367#4061367 

I am using the LMK03318 in Hardmode with ROM Option 45 to provide 3 LVPECL clocks to the TMS320C6678 (LJCB/CML inputs). My question is regarding the best input voltage level for the TMS320C6678. Currently the only circuitry between these two ICs is a 0.1uF capacitor. Please see the attached Word document for a discussion. Also please see the attached spreadsheet, which has 3 tabs showing the voltages from the Hyperlynx simulation of my present design.

As described on pages 4 and 5 of SCAA059C, should I add Ra series resistors?

What resistor value for Ra should I use?

Regards,

Larry

LVPECL to LJCB voltage adjustment.docxDAR6 Hyperlynx Simulations 4-20-2022.xlsx