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[FAQ] TDP1204: When to AC or DC couple the HDMI 2.1 output?

Part Number: TDP1204

Up until HDMI 2.1, source output AC coupling was not clearly defined. However, now with HDMI 2.1 AC coupling is clearly defined. However, how can the designer determine when to AC or DC couple the HDMI 2.1 output?

  • Whether to AC-coupled or DC-coupled the output or TX side of the device depends on the system design power versus filtering low frequency noise requirement trade-off. The power consumption will be higher with an AC-coupled output. However, the AC-coupling of the output of the device will block any DC or lower level noise frequencies that may be coupled onto the HDMI FRL lanes. For source AC coupled output, pull-down resistors are required to set the common mode voltage to HDMI compliant levels as shown in the picture below. Note, that these may be removed in the latest HDMI spec as long as the TP2_EQ eye diagram is met.

    Please see the TDP1204 power requirements in the photo below for more information on the power consumption differences.

    If power consumption is a concern, then the designer should  look to implement a DC-coupled output which will decrease the power consumption when compared to the AC-coupled output.