TMDS181: upper limit of TMDS181's in series connection

Jimmy Lai

Expert 6845 points

Part Number: TMDS181

Dear Team,

Customers want to know what the upper limit of TMDS181's actually tested series connection is?

Many Thanks,

Jimmy

over 3 years ago

0 David (ASIC) Liu over 3 years ago

TI__Guru**** 177301 points

Jimmy

Are you asking if there is a upper limit of multiple TMDS181 being daisy chained?

Thanks
David

0 Jimmy Lai over 3 years ago in reply to David (ASIC) Liu

TI__Expert 6845 points

Hi David,

Yes, the customer asked us whether we have tested how many ABCs can be connected in series?
If yes, what is the upper limit?

Many Thanks,

Jimmy

0 David (ASIC) Liu over 3 years ago in reply to Jimmy Lai

TI__Guru**** 177301 points

Jimmy

We never tested daisy chain multiple TMDS181 together in the lab. The TMDS181 is a retimer and when daisy chained, this can create PLL peaking which will degrade the TMDS181 performance.

Thanks

David

0 Jimmy Lai over 3 years ago in reply to David (ASIC) Liu

TI__Expert 6845 points

Hi David,

Could you help to explain what is "PLL peaking" ? Thanks!

I think the signal pass throw retimer to do the clock recovery and the jitter will be reduced.

If I have any misunderstandings, please let me know.

Many Thanks,

Jimmy

0 David (ASIC) Liu over 3 years ago in reply to Jimmy Lai

TI__Guru**** 177301 points

Jimmy

For the PLL, there is a small amount of amplification near the loop bandwidth. This amplification is called jitter peaking. This is the nature of the PLL design.

When you connect multiple TMDS181 together with identical PLL bandwidth, the jitter peaking from each PLL will result in a combined jitter peaking. The more TMDS181 you add, the bigger the PLL peaking which will degrade the system performance.

Thanks

David

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TMDS181: upper limit of TMDS181's in series connection