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Relation between crystal oscillator frequency and ppm

Dear all, Sorry if this looks novice.I am not able to correlate the relation between crystal oscillator frequency and ppm? What does the following sentence mean? "When a voltage is applied to the VCXO varacitors, the 27 MHz center frequency can be adjusted by approximately +/-150ppm (+/-4050Hz). "

We are offlate finding problems in the oscillator frequencies giving erroneous results in some of the products manufactured over a batch.Problem here is not all products in that batch have trouble only

10 out of 1000 products have the problem.We are supposed to provide color video pictures on a TV with our product and in some Tvs alone the color does not appear.This seems puzzling to me,and my customers state that the problem would be with color subcarrier frequency which inturn is controlled with the crystal oscillator.With respect to this,the above sentence in quotes was said which I am not able to comprehend.

Looking farward for all your replies and advanced thanks for the same, Regards, s.subbarayan

Reply to
ssubbarayan
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ppm stands for parts-per-million. In the given example, 150 ppm of 27Mhz equals 27E6 * 150 / 1E6 = 4050 Hz. The given sentence tells you that you can tune the oscillator from 27004050 to 26995950.

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Reply to
Ico

PPM stands for "parts per million", in this case parts per million of the carrier frequency.

So you routinely manufacture products without having a clue about the standards that are established for their proper working? You don't know about NTSC or PAL video standards? How nice.

Get yourself a copy of "Video Demystified". It won't instill a respect for standards into your soul, but should you acquire such respect elsewhere it'll help you understand video, and list out the standards that you need to design to.

Having raked you over the coals a bit, I should also mention that unless you're piping your video into some truly professional gear you should be able to get away with significant deviations from the standards -- video monitors are often quite tolerant of out-of-spec signals, although VCRs aren't, and pro equipment _really_ isn't.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

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