• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 32 subscribers
  • Views 820 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DS90UB936-Q1: S11, S21 measurement for DS90UB936 paired with DS90UB913A

Atsushi Hirai
Expert 4930 points
Part Number: DS90UB936-Q1

Hi FPD Link team,

My customer is evaluating the insertion loss and return loss of their PCB which has UB936. Conditions are as follows.

Target Serializer is UB913A
COAX with power over
RAW10 mode, 1.18Gbps forward channel Link, 2.5Mbps back channel Link
Goal is meeting suggested characteristics specified on UB936 datasheet Table 227.

There are several questions.
1) During the measurement, UB936 should be enabled and the back channel driver should be disable(0x58[4]=1), right?
2) For Table 227 on UB936 datasheet, why the frequency conditions are different between S11 and S21?
3) In the customer's use case, should they meet S11 spec from 1/2fBCC to 0.59GHz frequency range and S21 spec of "f < 0.5GHz" and "f = 1GHz"?(Can they ignore "f = 2.1GHz" spec?)

Please give us your advice.
Best Regards,

  • 0
    TI__Guru** 103215 points
    Hello Atsushi,

    1. Yes, this is correct
    2. S11 and S21 are relevant for different considerations. S11 is characterizing the impact of impedance continuity and reflections, while S21 is giving a loss parameter which is primarily of concern only for the forward channel because the frequency is much higher and will be attenuated more
    3. Please follow the entire table below - don't ignore and frequency range since digital signals contain spectral content outside of the fundamental frequencies

    Best Regards,
    Casey
  • 0 in reply to Casey McCrea
    TI__Expert 4930 points

    Casey-san,

    Thank you for your response. The customer understand it.

    I received one additional question. Please give me your advice again.

    The frequency range of -20dB return loss spec is mentioned "1/2 fBCC < f < 0.1GHz" but, how much the "1/2 fBCC" in the customer's use case?

    In my understanding, the back channel data rate is 2.5Mbps, the frequency(fBCC) is 1.25MHz so, the "1/2 fBCC" is 0.625MHz. is my understanding correct?

    On the other hand, the datasheet also has below paragraph.

    It says "1/2 fBCC" is 2.5MHz in 5Mbps back channel data rate case. which is correct?

    Regards,

  • 0 in reply to Atsushi Hirai
    TI__Guru** 103215 points
    Hello Atsushi,

    There are some errors in the datasheet section that you sent. The default backchannel speed for 913A compatibility is 2.5Mbps, and since the back channel is manchester encoded, the fBCC frequency is 2.5MHz as well. So for the return loss spec, the 1/2fBCC = 1.25Mhz.

    Best Regards,
    Casey
  • 0 in reply to Casey McCrea
    TI__Expert 4930 points
    Casey-san,

    Got it, thanks.
    Please revise the error at the next datasheet update.

    Best Regards,
  • 0 in reply to Atsushi Hirai
    TI__Guru** 103215 points
    Hey Atsushi,

    I flagged it for the next revision.

    Best Regards,
    Casey