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LMK04808 channel Output to Output Isolation

robinfeng
Intellectual 960 points
Other Parts Discussed in Thread: LMK04808, CDCE62005, LMK04805

Customer want to know the LMK04808 channel isolation. such as output frequency on channle 0, how many dBc you can measured on channel 1?

this parameter can be find on CDCE62005 datasheet page 20, but i can not find on LMK04808.

  • 0
    TI__Mastermind 28560 points

    Hello,

    Is there a particular frequency case you are interested in?  Outputs formats?  Particular clock outputs?

    73,

    Timothy

  • 0 in reply to Timothy T
    TI__Intellectual 960 points

    184.32M and 122.88M is prefered. LVPECL or LVDS is used in most of application.Thanks.

  • 0 in reply to Timothy T
    TI__Intellectual 960 points

    Reference:30.72MHZ，VCO = 2211.84MHZ，pre=3，out4 output 184.32MHZ，lvpecl，out5 =122.88MHZ，lvpecl。

     
  • 0 in reply to robinfeng
    TI__Mastermind 28560 points

    Thank-you for the additional information.  We will post crosstalk information next week.

  • 0 in reply to Timothy T
    TI__Mastermind 28560 points

    Hello,

    Your test frequency of 2211.84 MHz is an LMK04805 test frequency.  I tested with LMK04805.

    Also CLKout4 and CLKout5 belong to the same clock group which means they share a divider and can only have the same output frequency.  I shifted to CLKout3 and CLKout4 for the crosstalk test.

    For these tests I used a differential input reference of 30.72 MHz to CLKin0.  The VCXO used was the evaluation board 122.88 MHz LVCMOS VCXO, this may also cause some contribution to 122.88 MHz spurs.

    For adjacent channels CLKout3 & 4, I tested the direct couple spur and the 61.44 MHz GCD inter-modulation spur using LVPECL 1.6 Vpp mode.  I used a balun on output of CLKout3 and 4 when making observation measurements.

    122.88 MHz between 3 & 4 is about -75 to -79 dBc

    184.32 MHz between 3 & 4 is about -68 to -70 dBc

    61.44 MHz GCD is about -62 to -65 dBc

    Ultimately, it is best to test spurious in your specific application because of PCB effects.  Spurious measurements are not always accurate as phases of different signals can build up or cancel out.  Tightly coupled differential traces help reduce crosstalk.  Isolating power supply of clock groups operating at different frequencies using ferrite beads can also reduce crosstalk.  Please see datasheet for more information.

    73,

    Timothy