• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 3 answers
  • Subscribers 34 subscribers
  • Views 556 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLK2711-SP: AC coupling capacitor

Ryuuichi machida
Guru 12875 points
Part Number: TLK2711-SP


Hello,

Let me confirm concept of AC coupling for EVM and 9.2 Typical Application of datasheet.

According to 8.4.3 High-Speed I/O AC-Coupled Mode of datasheet, TI recommend user implement AC coupling capacitor on only RX side.

However, both EVM and 9.2 Typical Application of datasheet show that AC coupling capacitors are implemented on both TX and RX side.

In fact, I believe that series capacitor will reduce capacitor value. So, could you please tell me why EVM and 9.2 Typical Application of datasheet show implemention of AC coupling cap for both side ?

Best Regards,

  • 0
    TI__Mastermind 43795 points

    Not all in system receivers or benchtop test equipment is compatible with the TLK2711 output common mode voltage.  The AC coupling capacitors are used to overcome this issue and allow TLK2711 outputs to be connected to a wide variety of receivers.  AC coupling is almost universal in high speed serial communication.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Guru 12875 points

    Hello,

    The AC coupling capacitors are used to overcome this issue and allow TLK2711 outputs to be connected to a wide variety of receivers. 

    What klind of issue user can overcome by using AC coupling capacitors (I believe that you mentioned that user use multiple capacitor.) ?

    To solve common mode issue b/w transmitter and receive side, I believe that user just implement one AC coupling on either side.

    Could you please correct me if my understanding is incorrect ?

    Best Regards,

  • 0 in reply to Ryuuichi machida
    TI__Mastermind 43795 points

    Hi Ryuuichi,

    Yes, just one AC capacitor is required.  It is not necessary to have two or more capacitors in series.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Guru 12875 points

    Hi,

    >Yes, just one AC capacitor is required.  It is not necessary to have two or more capacitors in series.

    So, could you request to change datasheet about following section if there is no usecase which series capacitors are necessary ?

    "9.2 Typical Application of datasheet"

    Best Regards,

  • 0 in reply to Ryuuichi machida
    Guru 12875 points

    Hi,

    Could you please send me about your feedback ?

    Best Regards,

  • 0 in reply to Ryuuichi machida
    TI__Mastermind 43795 points

    Hi,

    AC coupling is a common technique used in serial communication protocols.  For the TLK2711 many applications are AC coupled to account for differences in the transmit output common mode voltage and the connected receiver common mode voltage requirements.  The AC coupling leaves the receiver able to self bias the input common mode to its ideal voltage level.

    If one TLK2711 is connected directly to another TLK2711 in a HS-Tx to HS-Rx situation the transmit and receive common mode specifications align.  This may allow for direct connection between the two devices.

    Regards,

    Lee