• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 21 subscribers
  • Views 446 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.

LMK03806B: LVPECL (1200mVpp) output Tr/Tf

toshi-e2e
Genius 4850 points
Other Parts Discussed in Thread: LMK03806

Hi all,
My customer has tried to use LMK03806B as the clock generator for the processor.
And the LVPECL output rise and fall time of  LMK03806B does not meet the CLKIN requirements.
The measured Tr/Tf time is about 400ps.
The output configuration is an AC-Coupled with 150-ohm emitter registers. 

I am happy to receive your advice for decreasing the Tr/Tf time.

 Required specification of CLKIN
==========================

                                                                     Min        Nom       Max

Input voltage, Differential PTP                         800        1000     1400      (mV)              AC Coupled

Input Common-Mode Voltage                               -          750             -       (mV)             Set by an internal bias circuit

Frequency Range                                                    -    156.25             -       (MHz)

Total Phase Jitter                                                     -               -         1.5      (ps)                Integrated between 12kHz and 20MHz

Duty Cycle                                                              45            50          55      (%UI)

Reference clock rise time 20%/80%                   -          200        300      (ps)               * measured Tr time is about 400ps.

Reference clock fall time 20%/80%                     -          200        300      (ps)               * measured Tf time is about  400ps.

Thanks in advance.
Regards,
Toshi

  • 0
    TI__Mastermind 24205 points

    Hi Toshi-San,

    Can the customer try the following:

    1) Reduce the value of the AC coupling capacitor: Not sure what value it is at now but they can try reducing it

    2) Change CLKoutX_TYPE = 5 (2VPECL mode) if they can tolerate a higher differential swing. This could help to improve the slew rate of the signal. Note that 2VPECL setting corresponds to a single ended swing between 800mV-1200mV.

    What is the common mode tolerance of the receiver? Perhaps the customer can try to DC couple the output of LMK03806 to their processor inputs?

    Regards

    Arvind Sridhar

  • 0 in reply to Arvind Sridhar
    Genius 4850 points
    Hi Arvind-san,
    Thanks for your support.

    They tried to 0.01uF of the AC coupling cap, but it's not affect.
    What is the recommended value of capacitor?

    About setting 2VPECL, the maximum input voltage range is 1.4Vpp. So I think it's impossible to set 2VPECL.

    The receiver's common mode voltage is 750mV. And its datasheet mentioned AC coupling is required.
    But I will ask them to try the DC coupling.

    Regards,
    Toshi