LMKDB1202: Cascade Questions

Allan Fan

Part Number: LMKDB1202
Other Parts Discussed in Thread: LMKDB1204

Hi experts,

Regarding the PCIe Gen6 RefClk: will it still function properly if it passes through 3 or 4 CLK buffers? Customer is considering LMKDB1204 and LMKDB1202. How should we estimate or evaluate the cumulative impact of cascading these buffers? Note that the specifications for the first buffer are currently unknown, as it depends on the specific motherboard design.

BR,

Allan

2 months ago

0 Michael Srinivasan 2 months ago

TI__Genius 16401 points

Hi Allan,

The reference clock will still function properly if passed through several consecutive buffers. There is some additive phase noise that will be introduced by the buffer, but it will be quite low. When compared to alternatively driving the signal through a long trace, the phase noise performance is much better when driving the signal between multiple buffers. I have attached a brief powerpoint with some measurements I collected on this topic, using the same core as the LMKDB1202. Gigabyte_LongTrace_Verification.pptx

Thanks,

Michael

0 Allan Fan 1 month ago in reply to Michael Srinivasan

TI__Expert 7730 points

Hi Michael,

According to the attached PPT, jitter increases as the buffer count increases. When cascading up to 4 buffers, will the jitter exceed the PCIe FEN6 CLK specification?

BR,

Allan

0 Michael Srinivasan 1 month ago in reply to Allan Fan

TI__Genius 16401 points

Hi Allan,

The jitter will increase, but not enough to exceed the PCIe FEN6 CLK specification.

Thanks,

Michael

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LMKDB1202: Cascade Questions