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DP83822IF: Data sheet spec question in 100Base-FX Mode

Magid Fazel
Prodigy 60 points
Part Number: DP83822IF

Hi,

Referring to the datasheet for DP8322IF when configured in 100Base-FX mode. 

Table 7.5 shows 

MDI 100BASE-FX receiver input swing requirement 0.22V to 1.8V

MDI 100BASE-FX transmitter swing 0.9V to 1.1V*

(*) with default setting.

Figure 7-20. 100BASE-FX Waveform 

Shows a waveform about 0.5V peak to peak.

 

Q1- Is the waveform shown centered around 0V?

Q2-Is this the expected waveforms at the input to the chip in 100BaseFX mode? I.e. is this for RX?  

Q3-Do you have a picture of the Transmit waveform?

Thanks

Magid

  • 0
    TI__Genius 16862 points

    Hi Magid,

    Figure 7-20 shows transmit waveform with ~1V peak to peak (500mV/div).

    Please allow me until Thursday 5/23 to check for more information on your questions.

    Thank you,

    Evan

  • 0 in reply to Evan Mayhew
    Prodigy 60 points

    Hi Evan,

    Thursday sounds good. The default TX drive configuration is max. 1111 = 1.033-V (Default Setting)

    Figure 7-20 is definitely NOT 1V. Each div is 500mV. IT looks more like 600-700mVpp.

    Figure 9-3 shows 50 OHM termination pullups to 3.3V. So, the RX signal at the input to the PHY chip should be riding 3.3V. 

    The TX signals at the PHY should also have a DC bias. After the AC cap the AC is of course removed going to the F/O XCVR.

    I do see the DC bias when I scope the PHY side.

    Thanks

    Magid 

  • 0 in reply to Magid Fazel
    TI__Genius 16862 points

    Hi Magid,

    Q1: Waveform is centered around 0V.

    Q2: This waveform is for the expected transmit output:

    This ~1V peak-to-peak swing is acceptable for the input level as well - the acceptable input swing ranges from 0.22 to 1.8 Vpk-pk.

    Q3: Figure 7-20 is the only reference we have for fiber transmit output levels. We have measured this in lab before and saw similar ~1V swing.

    What DC bias are you seeing? Can you share the fiber termination section of the schematic?

    Thank you,

    Evan