• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 215 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.

TLK2501: Amplitude of GTX_CLK

CK
Prodigy 10 points
Part Number: TLK2501

I tried to use a CG635 clock source to drive the GTX_CLK directly, but the measured amplitude of GTX_CLK is much smaller compared to the setting at CG635. Similarly when I use the LVCMOS18 output clock from AD9255

to drive the GTX_CLK, the amplitude is only about 500mV, but when the AD9255 output is not connected to TLK2501, the measured amplitude is close to 1.8. 

What is the recommended termination for GTX_CLK. The datasheet shows it is internal pulled-up. For the TXD data pins, the datasheet shows they are internal pull-down, looks like it can be driven by LVCMOS18 rightly.

  • 0
    TI__Mastermind 36373 points

    Hi,

    This seems puzzling since GTX_CLK is high impedance (see below).  Could you share your schematic?  Also, have you tried this with multiple TLK2501, or just one?

    Can you also share the amplitude and DC offset of the clocks you have used for testing?  How is the amplitude impacted by adding a small load, perhaps around 1kOhm.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Prodigy 10 points

    I used the circuit form the TLK2501 evaluation board: with 50-ohm pull down to GND. After changing it to serial termination with a 47 ohm between the clock source and the GTX_CLK. It works now.

  • 0 in reply to CK
    TI__Mastermind 36373 points

    Hi,

    Glad you figured it out.  The EVM has the 50 Ohm since the clock was designed to be input via an SMA connector.  This would imply that the EVM was expecting a 50 Ohm source.

    Thanks,
    Drew