How RMS phase jitter in frequency domain is calculated using phase noise plots

Phase noise describes jitter in the frequency domain. From the phase noise information, you can extract the RMS Phase Jitter value which is often given in datasheets as a measure of quality and spectral purity. The frequency spectrum plot in Figure 1 is of a real sinusoidal clock with nominal frequency Fc (also called the carrier frequency) plus sideband offset noise frequencies Fo. That means, sometimes the clock will have a slightly larger frequency Fc + Fo and sometimes it will have a slightly lower frequency Fc - Fo. The small changes in frequency appear as phase shifts in the clock waveform, hence the name phase noise. The noise power in a 1Hz band at an offset frequency Fo compared to the power of the carrier frequency Fc is called the dBc Phase Noise (dBc = power in dB relative to carrier). Refer to application note AN-815 for more details. For other questions not addressed by the Knowledge Base, please submit a technical support request.




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Application Notes & White Papers
AN-815 Understanding Jitter Units Application Note PDF 476 KB Apr 23, 2014