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Altera_Forum's avatar
Altera_Forum
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9 years ago

CPLD EPM570 internal oscillator clock stability

Hello,

I understand the absolute frequency of the internal oscillator is not known and varies with temperature and device charge between 3.3 MHz and 5.5 MHz. Fortunately for my project the absolute frequency is not important, however I want to use it to detect changes in an incoming signal and thus need to know about short / long term stability of the internal oscillator.

If the temperature is held at a constant level, what is the jitter/spread of the internal oscillators frequency over short time (e.g. 10ms to 1 sec)? Is the frequency variation in the 100ppm range or 1e-3 or higher? Unfortunately I could not find any info about the short term frequency variations.

Best Regards

Henning

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
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    9 years ago

    The internal oscillator isn't intended for precise timing purposes, so it's pretty understandable that no other parameters than frequency range are specified. You should measure it yourself.

    Just for comparison, I see with the MAX10 internal oscillator about 1e-3 relative jitter, e.g. 1 ns peak-to-peak after 1 µs delay. Short term stability seems acceptable.