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Regarding the DS90CR483a/484A device SI simulation query

Jeyalakshmi Kanniah1
Prodigy 170 points
Other Parts Discussed in Thread: DS90CR483A, DS90CR483, DS90CR484

Hi,

I have used the DS90CR483A/484A devices in design and schematic is attached here.

 Models Used:

U13 – DS90CR483(Transmitter)

J6 - DS90CR484Schematic.docx

Problem Description: Actual accepted swing level is 450mv(max). But in this case, I am seeing 2V signal levels.

 Please let me know, why the signal level is raised to unexpected levels or lf I am missing anything in the simulation.

 Thanks,

Jeyalakshmi

  • 0
    TI__Mastermind 29635 points
    Hi Jeyalakshmi,

    It's tough to tell just from this one schematic and one scope shot. Please help provide more details about what is going on:

    1. Do you have more information that you can provide about specific settings you used to program the DS90CR483 and DS90CR484 model, such as pre-emphasis?
    2. Do you have a scope shot from each individual transmitter output and receiver output?
    3, Does the signal amplitude scale with different Tx output settings?

    Thanks,

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Prodigy 170 points

    Hi Michael,

    Thanks for the reply and my response below.


    1. Do you have more information that you can provide about specific settings you used to program the DS90CR483 and DS90CR484 model, such as pre-emphasis?  - I havent changed the Pre-emphasis value in IBIS and there is no option for editing the parameter. Please let me know how to edit that.
    2. Do you have a scope shot from each individual transmitter output and receiver output? - Please find the attached document.3073.Schematic.docx
    3, Does the signal amplitude scale with different Tx output settings? - No. I am not able to find the way edit the output settings in Model. Kindly check and let me know.

    Thanks,

    Jeyalakshmi

  • 0 in reply to Jeyalakshmi Kanniah1
    TI__Mastermind 29635 points

    Hi Jeyalakshmi,

    I tried a simulation in Hyperlynx with a simpler schematic design, where I made a coupled stackup for the T-Lines and only have a 100-ohm resistor across the CR484 inputs:

    I made the coupled inputs so that they were 100-ohm differential, and I also used an ideal 100-ohm resistor across the DS90CR484 inputs.

    The output waveforms on the oscilloscope are below:

    Orange = DS90CR483 TXOUT5-

    Purple = DS90CR483 TXOUT5+

    Pink = DS90CR484 Differential Input

    The inputs I am seeing for the CR484 are within the +/-450 mV datasheet spec. From the simulation result, I am now guessing that there may be some reflection causing very high differential voltage across the LVDS pair. Would it be possible for you to share your simulation .ffs file? I think that may help us draw conclusions about what is going on.

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Prodigy 170 points
    Hi Michael,
    I am not able to attach the schematic file. Can you please share your mail id.

    Parameters used for Simulation:
    The frequency is 500MHz and the Trace length is 0.89inch.

    The inputs I am seeing for the CR484 are within the +/-450 mV datasheet spec - I am not able to find these values form datasheet.
    Thanks,
    Jeyalakshmi
  • 0 in reply to Jeyalakshmi Kanniah1
    TI__Mastermind 29635 points
    Hi Jeyalakshmi,

    I will send you an e-mail with the address you have used to register your TI account.

    Regarding the comment on the +/-450 mV spec, I'm referring to the LVDS Driver DC Specifications for VOD, where the max swing is +/- 450 mV. The LVDS Receiver DC Specification only requires that the differential swing surpasses a threshold of +/-100 mV.

    Thanks,

    Michael