8305AGI www.idt.com REV. B SEPTEMBER 17, 2012
7
ICS8305I
LOW SKEW, 1-TO-4, MULTIPLEXED DIFFERENTIAL/
LVCMOS-TO-LVCMOS/LVTTL FANOUT BUFFER
ADDITIVE PHASE JITTER
Input/Output Additive
Phase Jitter at 155.52MHz
= 0.04ps typical
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140
-150
-160
-170
-180
-190
100 1k 10k 100k 1M 10M 100M
The spectral purity in a band at a specific offset from the funda-
mental 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 fun-
damental frequency to the power value of the fundamental. This
ratio is expressed in decibels (dBm) or a ratio of the power in
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 de-
the 1Hz band to the power in the fundamental. When the re-
quired offset is specified, the phase noise is called a
dBc
value,
which simply means dBm at a specified offset from the funda-
mental. 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.
vice 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.
OFFSET FROM CARRIER FREQUENCY (HZ)
SSB PHASE NOISE dBc/HZ
