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©2015 Integrated Device Technology, Inc.

Revision C, December 8, 2015

8545 Datasheet

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 have

issues. The primary issue relates 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.

Offset Frequency (Hz)