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LMH1983: LMH1983 VCXO jitter requirement

Prodigy 180 points

Replies: 12

Views: 608

Part Number: LMH1983

Hi,

I've designed in the LMH1983 + LMH1981 to generate my 148.5MHz for an HD-SDI interface with a GS2972 SemTech device.

Currently I have design in the CTS 27MHz VCXO recommended in the datasheet/app note, but it's very large and would like to source a smaller alternative. I'm considering an Epson VG-4231CE 27MHz stability 37ppm APR 100ppm and I beleive the Jitter is 50ps maximum. It's onlys 3.2x2.5mm. Is this part suitable?

Thanks, Paul

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  • Can you please request & provide the phase noise data from 1 or 10 Hz up to 1 MHz for the VCXO part number you're considering to use?

    Regards,

    Alan

  • In reply to Alan O:

    Hi,

    currently looking most promising is this part

    https://www.geyer-electronic.com/uploads/tx_userartikelfrequenz/GEYER-KXO-72-VCXO-HCMOS_01.pdf

    -80 dBc/Hz at 10 Hz

    -110 dBc/Hz at 100 H

    -135 dBc/Hz at 1 kHz

    -140 dBc/Hz at 10 kHz

    -145 dBc/Hz at 100 kHz

    still awaiting answer from another supplier also.

  • In reply to Paul Carson1:

    The phase noise spec in the d atasheet does not specify the frequency of the measured clock, so it is not too helpful. The datasheet only gives the frequency range (1 MHz and 80 MHz) that can be ordered . Can you request the phase noise for the 27 MHz version? That would be most helpful.

    Regards,
    Alan
  • In reply to Alan O:

    Hi Alan,

    Epson have come back with what I hope is enough data....

    VG-4231CE_27MHz_Phase_Noise_Data_OUT-18-3935.pdf

    datasheet:

    VG-4231CE_en.pdf

    The planned part number is VG-4231CE 27.0000M-PSCM3  as it is x/s.

    This means a Stability 37ppm over 40C/+85C and an APR 140ppm (95ppm min).

    Vdd = 3.3v; Vc = 1.65v; 40/60 symmetry;

    Thanks,

    Paul

  • In reply to Paul Carson1:

    Paul,

    Thanks for the providing the data. This Epson P/N# should work well with LMH1983, as the phase noise is a little better than the CTS part.

    Regards,
    Alan
  • In reply to Alan O:

    thanks Alan, I'm going to getting the LMH1983 up and running in about 3 months, once PCBs populated so I'll undoubtably be in touch again!
    I'm still waiting on more data from Geyer also so I'll forward that also if I get it.
  • In reply to Alan O:

    should I be concerned about the higher APR?
    CTS was 50ppm whereas Epson is 95ppm.
  • In reply to Paul Carson1:

    A higher APR should not cause an issue.

    Alan
  • In reply to Alan O:

    Hi Alan,

    GEYER have come back with a reponse:

    Stability 50ppm over -40/+85C and APR 80ppm.

    Max Phase jitter 1ps

                GEYER               CTS

     dBc/Hz                 dBc/Hz

    @ 10Hz                  -80                      -60
    @ 100Hz               -110                     -90
    @1kHz                  -135                     -112
    @10kHz                -140                    -130  
    @100kHz             -145                     -150
    @1MHz                 -150                    -150 (> 100Khz)

    The Geyer 100kHz doesn't look just as good as CTS 357 series , but much better at lower frequencies so would it be good enough?

    CTS Model 357 008-0244-0_H.pdf27,000MHz KXO-72R VCXO - 3.3v 50ppm -40+85deg C.PDFThanks,

    Paul

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