For many communication applications, noise power in specific frequency range is of prime concern. Phase noise power is measured over the frequency range of interest in the frequency domain and converted in to an RMS value to represent a value in the time domain, which is known as phase jitter. Phase noise is the combined effect of different noise sources, such as thermal, shot, and 1/f noise. To measure phase jitter, phase noise in an offset frequency range (12 kHz to 20 MHz, for example) from the carrier frequency (100MHz, for example) is measured and converted into RMS value.
The offset frequency ranges for phase jitter measurements are application dependent. A couple of common application frequency range are:
1. 12 kHz to 20 MHz for SONET/SDH Application
2. 1.875 MHz to 20 MHz for Ethernet Application