Using ADN4650 for Isolating TMDS

Thank you for reading below my inquiry.

I'd like to use ADN4650 for Isolating TMDS (of HDMI by mainboard in computer), but ADN4650 is for isolating LVDS.

I found that TMDS's electrical specification is CML.

So, I need to converting circuits both CML->LVDS and LVDS->CML.

I'd like to designing compact circuit by passive parts like Resistor or Capacitor.

Motherboard(TMDS output of HDMI) -> (CML) -> Passive Circuit1 -> (LVDS)

-> ADN4650 -> (LVDS) -> Passive Circuit2 -> (CML) -> TV(TMDS input of HDMI)

Is it available for realizing this concept?

In Google, I found many solutions.

But, I want to find compact and proper solution for ADN4650.

How can I realize the schem for using ADN4650?

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  • 0
    •  Analog Employees 
    on Feb 12, 2018 2:53 PM

    Hi,

    Sorry, I didn't take enough time to correctly identify the sections of circuit I posted. The first one is actually LVDS to TMDS.

    The second circuit has AC coupling on the TMDS input, then to introduce the LVDS biasing, the pull-up and pull-down on Din-. And to answer your Q1, now we can see it introduces a common mode due to Din+ being tied to Din- with 200 Ohm (split termination with common mode biasing could also be used, but the biasing on Din- should be just as effective).

    Regarding Q2, our circuit assumed full isolation of a HDMI source. So on the isolated (cable) side, you need a power supply for isolator Vdd2s, as well as 5V/100 mA for HDMI to the sink. If you have sufficient 5V power on the source circuit, you can isolate using ADuM5000 x2. One ADuM5000 will provide the 5V/100 mA for the HDMI sink, and then the other will provide power for ADN4650 x2 and ADuM1250 x2. The latter will use a 5V supply, and the ADN4650 will require 2.5V on Vdd2 (ADP5302 will efficiently convert the voltage, allowing isoPower to be 5V->5V instead of the less efficient 5V->3.3V and then avoiding the LDO drop 3.3V to 2.5V using Vin2 to Vdd2 on ADN4650).

    For Q3, but looking at the first circuit, I think actually R5/R7 may not be required. The CML input at the HDMI sink will reference both TMDS+ and TMDS- to 5V.

    AC coupling is required as the CML/TMDS signals in HDMI are referenced to 5V, while LVDS receiver and driver operate at lower voltages, and either require a common mode around 1.2V on the input, or provide one on the output.

Reply
  • 0
    •  Analog Employees 
    on Feb 12, 2018 2:53 PM

    Hi,

    Sorry, I didn't take enough time to correctly identify the sections of circuit I posted. The first one is actually LVDS to TMDS.

    The second circuit has AC coupling on the TMDS input, then to introduce the LVDS biasing, the pull-up and pull-down on Din-. And to answer your Q1, now we can see it introduces a common mode due to Din+ being tied to Din- with 200 Ohm (split termination with common mode biasing could also be used, but the biasing on Din- should be just as effective).

    Regarding Q2, our circuit assumed full isolation of a HDMI source. So on the isolated (cable) side, you need a power supply for isolator Vdd2s, as well as 5V/100 mA for HDMI to the sink. If you have sufficient 5V power on the source circuit, you can isolate using ADuM5000 x2. One ADuM5000 will provide the 5V/100 mA for the HDMI sink, and then the other will provide power for ADN4650 x2 and ADuM1250 x2. The latter will use a 5V supply, and the ADN4650 will require 2.5V on Vdd2 (ADP5302 will efficiently convert the voltage, allowing isoPower to be 5V->5V instead of the less efficient 5V->3.3V and then avoiding the LDO drop 3.3V to 2.5V using Vin2 to Vdd2 on ADN4650).

    For Q3, but looking at the first circuit, I think actually R5/R7 may not be required. The CML input at the HDMI sink will reference both TMDS+ and TMDS- to 5V.

    AC coupling is required as the CML/TMDS signals in HDMI are referenced to 5V, while LVDS receiver and driver operate at lower voltages, and either require a common mode around 1.2V on the input, or provide one on the output.

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