Whether the HDMI interface of ADV7619 and ADV7441A can AC coupled? if yes, how to decide the coupling capacitor value?
Normally for high speed TMDS lines we use 100nF decoupling caps.
I have attached a reference design to AC couple our HDMI receivers. As mentioned before the ADV7441A is no longer recommended for new designs.
I have a similar situation, but additional questions.
I have a ADV7619 receiving an HDMI signal from an embedded SoC. The SoC's output signals are AC coupled with a Vswing measured at about 500mV on its evaluation board. When connected to a screen monitor the HDMI levels are roughly 3.3 +/- 250mV = 3.05 to 3.55V, (DC coupled scope signal). scope_111.png attached. The AC coupled scope signal, scope_108.png attached, shows more detail including some transitions with higher Vswing overshoot.
Q1 If I connect such a signal to the ADV7619, will that be OK for all HDMI rates to 4K30 ? The connection is on-board across 3"( 7cm) of FR4 ?
Q2 The signal exceeds AVCC of 3.3v but does that matter, or are there clamping diodes on the TMDS inputs that would clip a 3.6V signal?
Q3 If I use the AC coupling schematic from page 3 of your.ppt file (attached in the email thread) are the following correct?
3a. The mid level at the ADV7619 TMDS inputs will still be the termination voltage of 3.3V (for the dc balanced, ac coupled signal)
3b. The single ended Vswing seen at the receiver will be half that present on the HDMI input connection on the left, because the external 50ohms and internal ADV7619 50ohms are in series and act as a potential divider.
3c My V swing of 500mV will be halved to 250mV but that's still over the level the ADV7619 can receive.
Not sure if this file was successfully attached first time.
The AC coupled scope signal, scope_108.png attached, shows more detail including some transitions with higher Vswing overshoot.
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