Why DC Coupling or AC Coupling between TX & RX in Serial Interface?

[@balajiyoki8371]

Thanks for all these valuable information

[@circuitimage]

Hi Balaji, nice to meet you and thank you so much for the feedback. I'm glad that info helps. 😁

[@m_dawood371]

Excellent 5 seconds ;)

[@circuitimage]

Hi Engr, nice to meet you and I hope you liked it. Just give everyone has time to think about it before giving you the answer!! :)

[@kdh4301]

thank you😊

[@circuitimage]

Hi KDH, you are very welcome. Feel free to provide any feedback you had. :)

[@shadyEA60]

Thank you for good videos. Can you also post videos on power dc and power ac analysis?

[@circuitimage]

Hi shadiEA60, nice to meet you. Thank you for your suggestions and you are welcome. Sure. I'll do that. :)

[@hrachyakhachatryan1796]

Very useful video! I was always wondering why is this Manchester coding used in AUX port design, which also has AC coupled serial link. Now I see the reason. In Manchester coding, each data bit in encoded in such a way that it is high and low equal time (during one bit interval). Hence, it will avoid DC wandering and obviously will be way better DC balanced vs simple NRZ coding. One question. At 5:00, you have 50Ohm resistors to set CM levels on RX input. I assume that channel is also 50Ohm, and that is why you choose 50Ohm resistors to avoid reflection ? but why do we need to have 50Ohm resistors also on the TX side ?

[@circuitimage]

Hi Hrachya, nice to hear from you, and thanks for your feedback. You are correct about the 50ohm, which was for the RX input matching to the channel to avoid the reflection. Similarly, we don't want the reflection at the TX output; therefore, the TX output matching the channel (50ohm) impedance is still needed.

[@hrachyakhachatryan1796]

@@circuitimage thanks ))

[@circuitimage]

@@hrachyakhachatryan1796 You are very welcome.

[@mountaineagle4140]

Hi, CC, I have a question. In practice, ac couple cap might be placed close to RX side or TX side, which is better from circuit perspective? Some interface design guides such as GMSL3 suggest putting accap close to TX within 0.5UI. I could not find a good answer for this suggestion.

[@circuitimage]

Hi Mountain, nice to meet you, and thank you for the good questions. You are correct. Not every interface defines the placement of the AC coupled cap, but the GMSL3 (Gigabit Multimedia Serial Link) does define it near the TX. In addition, the AC coupled cap would be part of the TX's output matching network; therefore, it's suggested to put it within the TX