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LMK04828: DCLKoutX output termination when receiver has internal termination

Joe Miller1
Intellectual 315 points
Part Number: LMK04828
Other Parts Discussed in Thread: LMK04808

Dear Sir/Madam,

From a performance perspective (Phase noise and RMS jitter) is it better to use LVPECL or LVDS/HSDS when the receiver has internal termination.

The DCLKoutX frequency is 2600MHz and the receiver has internal termination.

Receiver:

HSDS 6ma, 8ma is suitable. 10ma is not
LVDS is suitable.
LVPECL 1600mV is suitable. 2000mV is not

Driver: PECL

Driver: LVDS/HSDS

Regards Joe

  • 0
    TI__Guru* 88960 points

    Hi Joe,

    Phase noise depends on the buffer type rather than the location of the termination. Noise floor of each buffer type is different. Also, the supported output frequency is different. In this case, you need 2.6GHz, I think only LVPECL can support. Noise floor of LVPECL is smallest vs LVDS/HSDS. The location of the termination will affect the waveform due to signal reflection.

  • 0
    Intellectual 315 points

    Dear Noel,

    Thank you for the reply.

    What frequency range is suitable for HSDS and LVPECL? 

    Regards Joe

  • +1 in reply to Joe Miller1
    TI__Guru* 88960 points

    Hi Joe,

    HDSD is similar to LVDS, the amplitude will drop significantly starting from 1.5GHz.

    LVPECL voltage swing drops gradually starting from 500MHz. At 3GHz, the voltage swing may drop to 500mV. 

    LMK04808 datasheet section 6.7 has some plots showing the voltage swing vs frequency.