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DS90UB933-Q1: How to messure the "power-over-coax supply noise"

Toshi
Expert 1780 points
Part Number: DS90UB933-Q1

Hi TI,

I'd Like to know the test condition and point of the " power-over-coax supply noise"  ?

Is it need to stop the back-channel signal ?

  • 0
    TI__Genius 10475 points
    Kobayashi-san,
    For the DS90UB933-Q1 the recommended operating conditions in the datasheet states < 35mVpp at DOUT for the frequency band specified in table 6.3.
    This is measured differentially between DOUT+ and DOUT-.
  • 0 in reply to Palaniappan Manickam
    Expert 1780 points

    Hi TI,

    thank you for your reply.   Well, I'd like to confirm the following points.

    1. About "This is measured differentially between DOUT+ and DOUT-." . 

        For the differential measurement, does It need to stop the back-channel  signal   ?  

    2. I guess it needs DPOJET for filtering frequency, correct ?

    3. I cannot understand the meaning of  "trise > 100us " , How to setup the DPOJET ? 

    4. I've found "Test ID 5.9: Source – Power over Coax interference noise level" in  CTP, 

         Is it same ?  Or different from  "power-over-coax supply noise" in the data sheet ?

  • 0 in reply to Toshi
    TI__Expert 8165 points

    Hello Kobayashi-san,

    1. The <35 mVp-p spec was derived by injecting noise before PoC filter on the SER side, measuring it across DOUT+ and DOUT- with a differential probe (FC and BC disabled), and then running the link under the worst case conditions (worst PVT corner, longest cable) with the FC and BC enabled to ensure error free operation.

    2. DPOJET may be used, but any is not necessary. Any oscilloscope differential probe with 200-250 MHz bandwidth is sufficient as the FC and BC are disabled.

    3. The CTP suggests measuring the imager/PoC interference signal (due to the 30/60 Hz blanking period) across the input capacitor of the regulator receiving the PoC voltage. Keeping the amplitude of the interference signal below 0.5V and the rise time of the interference signal above 100us (or the slew rate slower than 5mV/us) will ensure that the noise on the DOUT+ is less than 35 mV.

    4. It is related. The 500mV peak to peak noise on the switcher input (measured across CIN) with slew rate of >5mV/us will be attenuated by the high-pass filter (consisting of the ac-capacitors and termination resistors) to below 35 mV on the DOUT+ pin.

    Regards,
    Davor