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VCTCXO for CDCM7005

Karppa65
Prodigy 70 points
Other Parts Discussed in Thread: CDCM7005, DAC5682Z

Hi,

We have used Epson-Toyocom's TCO-2111T ( 768 MHz VCTCXO) as a clock source in our high-speed DAC design. The clock distribution circuit used is CDCM7005. Now we would like to find a backup / replacement for this VCTCXO, as delivery times tend to be very long.  Any suggestions?

  • 0
    TI__Mastermind 20900 points

    Hello,

    there is not a special recommended solution. You can take every VCXO that meets your specification regarding pullability, frequency.

    One thing you have to consider is the input leakage. It has to be as small as possible. Therefore, the input inpedance shoud be at least 1MOhm.

    regads,
    Julian hagedorn

  • 0 in reply to Julian Hagedorn
    Prodigy 70 points

    Hi Julian,

    Thank you for your reply. I have learned that there seems to be no off-the-shelf VCXOs on 700..800 MHz range, and the leadtimes are always long. I've found a couple of  good candidates (VFVX100 from Valpey Fisher and C5310A from Vectron). They have a good RMS jitter figure, which is important to our high-speed DAC design. We use TIs DAC5682Z @ 768 MHz, and provide samples to it at 192 MHz ( 4x interpolation). The basic design idea is about the same as in the DAC5682 EvKIt.

    Br, Karppa

  • 0 in reply to Karppa65
    TI__Expert 4150 points

    Hello Karppa,

    I have modified your post slightly to avoid discussing the performance of none-TI clock products. 

    To check whether a clock source is applicable to the DAC you should investigate into the required phase noise spec.  A publication in IEEE Transactions titled 'Direct Digital Synthesizer with Jittered Clock' by 'Yih-Chyun Jenq' shows that the phase noise (and therefore, SNR) of a DAC output tone is just 20*log10(fDAC/fIN)+3 dB better than the phase noise of the clock fed into the DAC. So the reference clock quality can limit your DAC performance.

    We will investigate a bit more into the VCXO topic and post an answer to your question here. Thank you & Best regards, Fritz