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DS30EA101: IBIS model's Vdiff parameter

Clyde Hinkle
Prodigy 20 points
Part Number: DS30EA101
Other Parts Discussed in Thread: DS30BA101,

The IBIS model provided on ti.com for this part has a Vdiff parameter of 2.5V. For a device that is capable of picking up signal through a cable path with 50dB attenuation and a source transmitter (DS30BA101) with typical differential output of 800mV into 100ohm twisted pair, that seems like an inaccurate vdiff setting. Hyperlynx modeling of a DS30BA101 to DS30EA101 link with TI's IBIS models doesn't provide functional output from the DS30EA101 even when it has a fairly clean and not very attenuated input signal, as compared to the modeled source signal from the DS30BA101. I found more reasonable operation if Vdiff for the DS30EA101 was changed for instance to 2.5mV (about 50dB attenuation from DS30BA101's 800mV typ Vdiff out). What is the true vdiff voltage for the DS30EA101? Is there any other documentation or validation report available confirming the performance of the rest of this IBIS model? 

Regards,

C W

  • 0
    TI__Guru* 93670 points

    Greetings,

    IBIS file mainly just tells us the I vs V or the output driver strength. However, it doesn't tell us about the EQ gain of the part. To check on the gain, we really need AMI model - unfortunately this is not available for this part. 

    DS30BA101 maximum 100-ohm differential output is about 800mV - with Rset close to 487 ohm. With this settings, DS30EA101 50dB equalizer can recover the signal.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser, 

    Thanks for responding so quickly. The gist of what I get from your response is that there's no useful modeling to be done with the IBIS models provided for these devices, so their existence is essentially superficial. 

    As far as Rset, I assume that you're referring to the Rvo pin pullup resistance value on the DSBA101. The datasheet recommends that value to be 953 ohms for 800mV differential output into 100 ohm differential cable. How did you come to a value of 487 ohms? 

    Regards,

    C W

  • 0 in reply to Clyde Hinkle
    TI__Guru* 93670 points

    Hi Clyde,

    With respect to IBIS file, your understanding is correct.

    Range of Rvo is from 953 ohm to 487 ohm corresponding to 800mV output differential to 1600mV output differential. 

    Regards,, Nasser

  • 0 in reply to Clyde Hinkle
    Prodigy 20 points

    Thanks Nasser.

    I noticed that you answered a related question a few years ago on the DS30EA101's available gain at 200MHz nyquist for 400MHz bitrate. For a bitrate configured between 800MHz and 2GHz and a DS30BA101 transmitter set with 953 ohm Rvo, what is the max cable attenuation that can still have a recovered bitstream by the DS30EA101? And I presume that for an anticipated max cable attenuation under those conditions, I could swap the Rvo to 487ohm and be able to get another 6dB of cable loss, correct? Are there minimum cable attenuations required for either of those operating configurations?

    Appreciate the help.

    C W

  • 0 in reply to Clyde Hinkle
    TI__Guru* 93670 points

    Gain at 800MHz to 2GHz could vary from 35dB to 45dB or so - max gain at 1.5GHz at 50dB. Further, as you noted you can sweep Rvo to 487 ohm to get longer reach or a higher eye opening if needed.

    Regards,, nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Will the DS30EA101 operate properly with a 1600mV differential signal on its input? (Essentially covering the case of the link configured for maximum cable length operation with Rvo=487 ohms but tested with a minimum attenuation cable connection.)

    C W

  • 0 in reply to Clyde Hinkle
    TI__Guru* 93670 points

    Hi Clyde,

    DS30EA101 is an adaptive equalizer and with minimum cable and high launch it would select a low EQ gain.

    Regards,, Nasser