8304I Data Sheet

©2015 Integrated Device Technology, Inc

December 10, 2015

6

ADDITIVE PHASE JITTER

The spectral purity in a band at a specific offset from the fundamental

compared to the power of the fundamental is called the dBc Phase

Noise. This value is normally expressed using a Phase noise plot

and is most often the specified plot in many applications. Phase

noise is defined as the ratio of the noise power present in a 1Hz

band at a specified offset from the fundamental frequency to the

power value of the fundamental. This ratio is expressed in decibels

As with most timing specifications, phase noise measurements has

issues relating to the limitations of the equipment. Often the noise

floor of the equipment is higher than the noise floor of the device.

(dBm) or a ratio of the power in the 1Hz band to the power in the

fundamental. When the required offset is specified, the phase noise

is called a dBc value, which simply means dBm at a specified offset

from the fundamental. By investigating jitter in the frequency domain,

we get a better understanding of its effects on the desired application

over the entire time record of the signal. It is mathematically possible

to calculate an expected bit error rate given a phase noise plot.

This is illustrated above. The device meets the noise floor of what

is shown, but can actually be lower. The phase noise is dependent

on the input source and measurement equipment.

Additive Phase Jitter @

125MHz (12kHz to 20MHz) = 0.17ps typical