DS160PR410: DJ in the output waveform

Naoki Yoneyama

Part Number: DS160PR410

Hi Team,

I would like to inquire about the concept of DJ (Deterministic Jitter) included in the output waveform of DS160PR410.

According to the datasheet, I noticed that there are multiple DJ values mentioned, namely TDJ-DATA, JITEER_INTRINSIC_SIC_DJ, and JITEER-INTRINSIC-TOTAL. It is stated that this redriver is compatible with PCIeGen4. Upon adding up these DJ values, the maximum value reaches 9.2ps, which is approximately 0.15UI (at 16Gbps).

Does the DJ included in the output waveform of DS160PR410 become the sum of the input waveform's DJ and the aforementioned 9.2ps? And, I thought that if the retimer adds 0.15UI of DJ, it could potentially impose a significant constraint in the link budget. Am I correct in my understanding? From the perspective of DJ, what are the scenarios or situations in which there are benefits to adopting this retimer?

7 months ago

0 David Waier 7 months ago

TI__Genius 15311 points

Hi Yoneyama-san,

Thank you for inquiring about the Dj parameters of the DS160PR410 redriver. Please give me a day to get back to you on your questions about Dj for this device.

Best,
David

0 Naoki Yoneyama 7 months ago in reply to David Waier

Prodigy 20 points

Hi David,

Could you please respond by 22nd Mar.?

Best,

Naoki

0 David Waier 7 months ago in reply to Naoki Yoneyama

TI__Genius 15311 points

Hi Yoneyama-san,

Yes, I will have feedback by 22 March.

Best,
David

0 David Waier 7 months ago in reply to David Waier

TI__Genius 15311 points

Hi Yoneyama-San,

The DJ values you've pointed out in the data sheet are for different test scenarios - please note the "Test Conditions" column.

Suggestion is to focus on INTRINSIC parameters listed for the redriver vs. baseline. At 8GHz, JITTER_INSTRINSIC-DJ is 1.2ps maximum and T_RJ-INSTRINSIC is 190fs. Total added jitter is approximately (1.2ps + .19ps) / 62 ~= 0.022 UI.

Best,
David

0 Naoki Yoneyama 7 months ago in reply to David Waier

Prodigy 20 points

Hi David,

I have understood that the DJ of this redriver's output waveform is added JITTER_INSTRINSIC-DJ and T_RJ-INSTRINSIC to the input waveform. The TDJ-DATA and TRJ-DATA are seemed to not be added to output waveform from your feedback, so what do these parameters mean?

Please also let us know what case it would be advantageous to adopt this redriver.

Best,

Naoki

0 David Waier 7 months ago in reply to Naoki Yoneyama

TI__Genius 15311 points

Hi Yoneyama-san,

These parameters are measured when using a different test pattern - note 16Gbps PRBS15 pattern is used in these test conditions.

The typical use case for PCIe redriver is to compensate for pre-channel insertion loss, as the redriver provides CTLE gain to the signal at its TX. Please note this white paper, Section 2.3, which highlights some of the use cases for PCIe redrivers.

Best,
David

0 Naoki Yoneyama 7 months ago in reply to David Waier

Prodigy 20 points

Hi David,

To summarize, is the added jitter to output waveform in the redriver as follows?

・For 16Gbps PRBS15, the added jitter in the redriver is TDJ-DATA and TRJ-DATA.

・For 8GHz CK, the added jitter in the redriver is JITTER_INSTRINSIC-DJ and T_RJ-INSTRINSIC.

I have confirmed in the white paper that the redriver’s beneficial case is described.

Best,

Naoki

+1 David Waier 7 months ago in reply to Naoki Yoneyama

TI__Genius 15311 points

Hi Yoneyama-san,

Your understanding is correct.

Best,
David

0 Naoki Yoneyama 7 months ago in reply to David Waier

Prodigy 20 points

Hi David,

Thanks for your great support.

Best,

Naoki

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DS160PR410: DJ in the output waveform