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Design >> RF Design >> frequency accuracy and phase noise of PLL
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Message started by tulip on May 9^th, 2015, 8:19pm

Title: frequency accuracy and phase noise of PLL
Post by tulip on May 9^th, 2015, 8:19pm

Hello everyone, I need to design two PLLs whose frequency differences is very accurate. I have several questions about this, please help me.
1. the concept of frequency accuracy and phase noise of pll.
In my opnion, frequency accuracy is usually expressed in ppm. It is determined by the reference frequency accuracy(crystal oscillator frequency accuracy). The other building blocks of PLL, such as divider, CP, VCO do not inflence the frequency accuracy.
Phase noise is a random process, building blocks of PLL, such as divider, CP, VCO do influence the phase noise.

2.I think frequency accuracy do not influence phase noise, but phase noise, as it is frequency fluctuation, will influence instantaneous frequency accuracy, not average frequency accuracy.

3.To improve average frequency accuracy, the only way is to select high accuracy frequency reference. To improve instantaneous frequency accuracy, we should select high accuracy frequency reference and optimize the phase noise of PLL.

4. from the above, it seems the only way to improve the average accuracy of PLL frequency differences is to select high accuracy frequency reference. If we need to improve the instantaneous accuracy of PLL frequency differences, we should also optimize the phase noise of PLLs.

Am I correct? Thank you very much.