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TMDS181: Transition Time definition

Hirokazu Takahashi
Expert 8420 points
Part Number: TMDS181
Other Parts Discussed in Thread: PCA9306

Dear Support team,

Could you please support below questions?

Q1. Does Transition Time, tT1(2.0) and tT1(1.4b) change by emphasis configuration?
Q2. Could you let me know the typ value of tT1(2.0) and tT1(1.4b)?
Q3. Why is the value of tT1(2.0) different from tT1(1.4b)? Is the reason related with termination resistance?
Q4. What will TX_TERM of TMDS181 change at 3 kinds of terminal resistance?

Best Regards,
Hirokazu Takahashi

  • 0
    TI__Mastermind 35130 points

    Hi Takahashi-san,

    1. Yes, de-emphasis would effect the transition time since it changes the level of the waveform. We do not have data for this test condition though. 

    2. Typical values on the bench were 130ps for 1.4b and 120ps for 2.0 for the test conditions listed in the datasheet.

    3. Yes, among other factors like datarate.

    4. Different TX_TERM is required by specification. For HDMI2.0, 75-150ohm is required. HDMI1.4b does not specify a termination resistance, so usually no termination or 150-300ohm termination is used. The termination mainly effects the swing.

    Regards,

    I.K.

  • 0 in reply to Ikechukwu Anyiam
    TI__Expert 8420 points

    Hello I.K. san

    Thank for your support.

    May I ask additional question below?

    Q5. Can TMDS181 emphasis transition time by any register?
    Q6. Is Transition Time, tT1(2.0) and tT1(1.4b) effected by input signal transition? It is different at Retimer or Redriver mode?
    Q7. Is it acceptable that HDMI signal for receiver site is active at non power supply condition?
    Q8. Could you let me know the wiring capacity for DDC?

    Best Regards,
    Hirokazu Takahashi

  • 0 in reply to Hirokazu Takahashi
    TI__Mastermind 35130 points

    Hi Takahashi-san,

    Sorry for the delay. I am looking into your additional questions and will have answers for you within the week.

    Regards,

    I.K. 

  • 0 in reply to Ikechukwu Anyiam
    TI__Mastermind 35130 points

    Takahashi-san,

    5. Register 0Ch (CLK/Data swing as well as de-emphasis control) would have an effect on on the transition time

    6. It is not effected by input signal transition 

    7. Yes that's fine

    8. We don't have the exact number for the capacitance of the SDA and SCL pins, but they should be in the order of 10pF

    Regards,

    I.K.  

  • 0 in reply to Ikechukwu Anyiam
    TI__Expert 8420 points

    Hello I.K. san

    Thanks for your support.
    Let me know more thing about No.8.
    In Source equipment, the wiring capacity of DDC lines (SDA and SCL) is standardized to 50pF or less.
    Therefore, if a part is put during the DDC line, the wiring capacity of the part will increase.
    When connecting TMDS181 into HDMI line,
    Is it necessary to add TMDS181 capacity?
    or can we ignore the capacity of TMDS181 for HDMI line?

    Best Regards,
    Hirokazu Takahashi

  • 0 in reply to Hirokazu Takahashi
    TI__Mastermind 35130 points

    Hi Takahashi-san,

    Sorry for the delay, I was out of office this past week. TMDS181 capacitance will need to be added. If this is a concern they can use an I2C level shifter like the PCA9306 to isolate the DDC capacitance.

    Regards,

    I.K. 

  • 0 in reply to Ikechukwu Anyiam
    TI__Expert 8420 points

    Hello I.K-san

    Thanks for you reply.
    Could you estimate the value for the capacitance?
    I wonder if it may be depended on lead frame.

    Best Regards,
    Hirokazu Takahashi

  • 0 in reply to Hirokazu Takahashi
    TI__Mastermind 35130 points

    Hi Takahashi-san,

    We don't have the exact number for the input capacitance of the SDA/SCL but it should be in the order of 10pF like most I2C slave devices.

    Regards,

    I.K.