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DS80PCI102: EQ running in PCIe Gen 1 Speed

SimonF
Expert 3350 points
Part Number: DS80PCI102
Other Parts Discussed in Thread: SN75DP139

Hi Team,

The device also provides equalization (CTLE) and de-emphasis capabilities. The question I have is related

to the EQ. We need to know, if the EQ is also available when the devices is used on a PCIe link running at Gen1 speed (2.5Gbps)?

To me, the DS doesn’t outline this explicitly. There is a footnote in the DS (below table 2) that can be read in a way, that

CTLE is not dedicated to Gen3 only and also working when the link is running Gen1. This would correspond to our experience, but it would be much appreciated if you can confirm this.

Best regards

SF

  • 0
    TI__Expert 3350 points
    Hi Team,
    any update here?
    Best regards
    SF
  • 0
    TI__Mastermind 29655 points
    Hi SF,

    Confirmed. The EQ is applicable across all data rates. However, note that the EQ is a frequency-dependent curve. That means that for lower frequencies, the same EQ setting will have less gain than when you approach the maximum frequency (Nyquist for 8 Gbps is 4 GHz). This is intended as a way to provide compensation for the frequency-dependent loss that is expected on the interconnect media between the source and the DS80PCI102 input pin.

    Thanks,

    Michael
  • 0
    TI__Mastermind 43795 points

    Hi SF,

    The de-emphasis function works are all three rates. 

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    TI__Expert 3350 points

    Hi Lee,

    thank you for your support!

    My customer has one additional question:

    The SN75DP139 provides three different settings to control the slew-rate for the TMDS outputs.

    This is controlled by the SRC pin. In our application we can control the level on this pin during runtime.

    We wanna use this in order to see what happens to the harmonics, especially for the HDMI clk signal,

    during EMI testing. However we couldn’t see any effect or difference with the spectrum analyzer.

    In the DS I didn’t find a meaningful explanation for this. Is it possible, that these settings are latched on

    power-on only? Or what else can be wrong?


    Can you change the slewrate settiungs while the device is up and running?

    Best Regards

    SF

  • 0 in reply to SimonF
    TI__Mastermind 43795 points

    Hi SF,

    I would also try to measure the slew rate at the device output with an oscilloscope.  The level of I2C_EN can also impact the output edge rate.  What is I2C_EN = ?

    Is the pin I2C_EN held at a constant value?

    Thanks and Regards,

    Lee