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TDP1204: Diff Impedance value

Hideki Hayashi1
Expert 8390 points
Part Number: TDP1204

Hi team,

Can customer set differential impedance (both input and output) as 100-ohm? Is it the requirement that impedance must be in range of below or just a design parameter?

Best regards,

Hayashi

  • TI__Genius 13310 points

    Hello,

    The termination for this device can be set by the TERM register. 

    Hideki Hayashi1 said:
    Can customer set differential impedance (both input and output) as 100-ohm?

    Yes. You can look at the 8.1 Functional Block Diagram to see that there are terminations on both sides RX/TX.

    Hideki Hayashi1 said:
    Is it the requirement that impedance must be in range of below or just a design parameter?

    The specs that you point out above are design parameters for the output and input traces on the PCB (see Figure 9-1. TDP1204 in Source Side Application). However, the requirement is that you need to be matching to those design parameters and it also depends on the HDMI version you are using.

    HDMI 2.0 standards require a source termination impedance approximately 100-Ω for data rates > 3.4-Gbps. HDMI 1.4b requires no source termination but has a provision for termination for higher data rates greater than 1.65-Gbps. Enabling this termination is optional. Table 8-13 lists how the TDP1204 terminations are controlled automatically when in pin strap mode. Depending on the MODE pin, the CFG0 pin can be used to select the HDMI 1.4 termination between open and 300-Ω.

    Thanks,

    Zach 

  • in reply to Zach Dryer
    TI__Expert 8390 points

    Hi Zach,

    The customer application is HDMI2.1. If so, from the HDMI2.1 standard, 100ohm termination is acceptable. And the device includes termination and also which can be set by Table 8-12. Customer is simply choose 2h or 3h at TERM register.

    What does the "AC-coupled HDMI" and  "DC-coupled HDMI"? I am not sure how to choose TX_AC_EN Register.

    From Table 8-13, HDMI2.1 termination spec is same as HDMI2.0, so the termination should be around 100ohm in DC coupled HDMI, and should be aroung 50ohm in AC coupled HDMI, is that correct?

    Best regards,

    Hayashi

  • in reply to Hideki Hayashi1
    TI__Mastermind 39105 points
    Hideki Hayashi1 said:
    Customer is simply choose 2h or 3h at TERM register

    Yes both of these register values should work for HDMI2.1 application. 

    Hideki Hayashi1 said:
    What does the "AC-coupled HDMI" and  "DC-coupled HDMI"? I am not sure how to choose TX_AC_EN Register.

    With HDMI2.1 the data signal can ow be AC or DC coupled. Have a look at section 9.2 and 9.3 for a source and sink design respectively. To determine if AC_EN is high or low you need to know if TX is DC or AC-coupled to HDMI receptacle? If its AC coupled then AC_EN = 1, if not AC_EN = 0

    Hideki Hayashi1 said:
    From Table 8-13, HDMI2.1 termination spec is same as HDMI2.0, so the termination should be around 100ohm in DC coupled HDMI, and should be aroung 50ohm in AC coupled HDMI, is that correct?

    Yes, this is correct. But just to reiterate it must be 50 ohm to supply. 

  • in reply to Vishesh Pithadiya
    TI__Guru**** 177151 points

    Hayashi-san

    Whether to AC-coupled or DC-coupled TX depends on the system design requirement. But the power consumption will be higher with AC coupled output. If power consumption is a concern, then I would go with the DC-coupled output.

    Thanks

    David