873033AM

www.icst.com/products/hiperclocks.html

REV. A OCTOBER 19, 2005

6

Integrated

Circuit

Systems, Inc.

ICS873033

Additive Phase Jitter

@ 155.52MHz (12kHz to 20MHz)

= 0.20ps typical

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

-180

-190

1k

10k

100k

1M

10M

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 (dBm) or a

As with most timing specifications, phase noise measure-

ments have issues. The primary issue relates to the limita-

tions of the equipment. Often the noise floor of the equipment

is higher than the noise floor of the device. This is illustrated

ratio of the power in the 1Hz band to the power in the funda-

mental. 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 fre-

quency 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.

above. The device meets the noise floor of what is shown, but

can actually be lower. The phase noise is dependant on the

input source and measurement equipment.