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AD725 oscillator options

Hello,

I want to use AD725 and made circuit to automatically detect NTSC and PAL, so that after that it will feed correct crystal oscillator to AD725.

I have 2 options:

1- get 2 oscillators, feed them through SPDT analog switch and make the circuit activate either one automatically.

2- as seen in this image. I got LTC1799 and made 2 resistor lines according to its datasheet to have 14.318180MHz or 17.734475MHz (please check if my calculations are correct). Here this part will deliver the correct frequency instead of having 2 oscillators now I got only one. Still going to use the analog switch as seen.

My issue is that option 2 is expensive and I would like to have option 1 or anything cheaper than option 2. Most oscillators here are 3.3v and most of them are out of stock.

I selected these 2 oscillators:

NTSC: www.digikey.com/.../11400465
PAL: https://www.digikey.com/en/products/detail/sitime/SIT8208AI-82-33E-17-734475/11459897

are they good? they are 3.3v and do not go to 5v, are they good enough with ad725 or the 2nd option is better?

thanks

Parents Reply
  • I have used these parts:

    ASE-14.31818MHZ-LC-T for NTSC -> 3.3v crystal-based.

    SIT8208AI-82-33E-17.734475 for PAL -> 3.3v, mems based. there is no crystal based one. this one says it is suitable for video in its datasheet.

    please check the circuit for enabling them here: https://slow.pics/c/LCR9bnbE

    circuit operation: both crystal oscillators EN\OE\ST are tied to ground via a pull-down resistor of 10k to make sure both are off. then analog switch chooses which one to activate based on "STND" signal. if STND is ON, then NTSC is the way to go and vice versa. Here analog switch won't affect the circuit since crystal outputs are directly tied to AD725 pin... the 2 crystal oscillators outputs are tied together but I don't think this will cause anything since one of them will on and the other is hi-z

    this is the best I could do besides LTC1799 which you didn't recommend.

    what do you think?

    notice that I can't do any manual adjustments or so on.

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