ICS831721I Data Sheet

DIFFERENTIAL CLOCK/DATA MULTIPLEXER

ICS831721AGI REVISION A AUGUST 19, 2011

6

©2011 Integrated Device Technology, Inc.

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 (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.

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. 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.

The source generator is the Rhode & Schwarz SMA 100A Signal

Generator 9kHz – 6GHz. Phase noise is measured with the Agilent

E5052A Signal source Analyzer.

Additive Phase Jitter @ 100MHz

12kHz to 20MHz = 0.314ps (typical)

Offset from Carrier Frequency (Hz)