Phase noise is measured in the frequency domain, and is expressed as a ratio of signal power to noise power measured in a 1Hz

bandwidth at an offset frequency from the carrier, e.g. 10Hz, 100Hz, 1kHz, 10kHz, 100kHz, etc. Phase noise measurement is made

with an Agilent E5052A Signal Source Analyzer (SSA) with built-in outstanding low-noise DC power supply source. The DC source

is floated from the ground and isolated from external noise to ensure accuracy and repeatability.

In order to determine the total noise power over a certain frequency range (bandwidth), the time domain must be analyzed in the

frequency domain, and then reconstructed in the time domain into an rms value with the unwanted frequencies excluded. This may be

done by converting L(f) back to Sφ(f) over the bandwidth of interest, integrating and performing some calculations.

The value of RMS jitter over the bandwidth of interest, e.g. 10kHz to 20MHz, 10Hz to 20MHz, represents 1 standard deviation of

phase jitter contributed by the noise in that defined bandwidth.

Figure below shows a typical Phase Noise/Phase jitter of a QT88L, 3.3Vdc, 20MHz clock at offset frequencies 10Hz to 5MHz, and