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Original question:

TLK1501: TLK1521 Replacement?

TLK1501: TLK1501 with SFP

user6019263
Prodigy 220 points
Part Number: TLK1501

Hi:

  my board has two tlk1521 and SFP Fiber channels , the frequency is 50MHz,when I test with twist wires with both of tlk1521 are ok(no SFP ), the lock signal is ok , and the RX clock can lock constant the 50MHz clock,  and I can received the data what I had send , when I use SFP, the RX clock  can not lock signal , and the RXD, TXD have some data even no data sending , actually I also had try use TLK1501, seems have same result . my question is below :

      i> does TLK1521 requires special SFP such as serdes SFP . if yes , could you pls recommended the Avago SFP model 

      ii> if no special SFP , what is the problem ?

      

  • 0
    TI__Mastermind 36153 points

    Hi,

    Can you provide a block diagram or schematic to help us better understand your system?

    What is your signal source when using twisted wires and SFP?  What sort of data pattern are you sending?  Have you measured the eye going to DINRX in both cases?  Is the signal AC coupled in both cases?

    Thanks,
    Drew

  • 0 in reply to Drew Miller1
    Prodigy 220 points

    Hi:

        Miller , thank you answer quickly 

    pls see below diagram .

       when I use optical SFP connect both PCB ,even 4 channel communication model not work , still found RX_clock can not locked properly .also  the tlk1521 RX side can measure some no used signal .

    when I use two twist wires connect each TLK1521 ，that means one twist wires connect one tlk1521 DOUTTXP and DOUTTXN and another tlk1521 DINRXP and DINRXN. another twist wires  connect one tlk1521 DINRXP and DINRXN and another tlk1521 DOUTTXP and DOUTTXN.both PCB works fine , RX_clock lock the send frequency, the 4 channel communication works good .

    so I suspect if SFP issue , I changed several different SFP , seem no improve . as I know ,normal SFP will work as Eithernet mode or SGMII mode at specified frequency .maybe  I need some kind of SFP which support Serdes mode at any frequency .

    would you pls give me advice , thank you . 

  • 0 in reply to user6019263
    TI__Mastermind 36153 points

    Hi,

    I believe an SFP module would be rated for 1.25 Gbps, while you are attempting to transmit data at 1.00 Gbps using a 50 MHz clock.  For 1.25 Gbps, I would try a 62.5 MHz clock.

    Beyond this, the other differences that come to mind between twisted pair and SFP is signal integrity and AC coupling.  Signal transmitted through an SFP would be AC coupled.  You might try adding AC coupling caps to your twisted wire test to see how this behaves.  I would also recommend comparing the eye diagram between twisted pair and SFP.

    Another thought: Have you tried a passive DAC SFP cable?

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Prodigy 220 points

    Hi：

        Miller ,thank you quick answer , actually, I had try 50MHz and 62.5MHz crystal , seem the same result , I can explain  more details as below :

       step 1: I use two twist wires connect both board with 4 0 ohm resistor.it is work , communication is ok , lock is ok . 

      step 2: changed 4 0 ohm resistors 100nF capacitor , both of board can not work , can not lock , also have random error. .

    as I know , tlk1521 have internal resistance config

    does anything wrong for me . 

    additionally, if I use tlk1501 , how can config the input and output . 

  • 0 in reply to user6019263
    TI__Mastermind 36153 points

    Hi,

    The TLK1501 requires external termination resistors.  Have you implemented these according to the figure below?  Are you using 50 Ohm termination resistors?

    Please also place the AC coupling capacitors close to the receivers, as shown in figure 16.

    Thanks,
    Drew