ICS8524 Datasheet, PDF (6/17 Pages) Integrated Circuit Systems – LOW SKEW, 1-TO-22 DIFFERENTIAL-TO-HSTL FANOUT BUFFER

ICS8524
LOW SKEW, 1-TO-22
DIFFERENTIAL-TO-HSTL FANOUT BUFFER
ADDITIVE PHASE JITTER
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
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.
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140
-150
-160
-170
-180
-190
1k
Input/Output Additive
Phase Jitter at 156.25MHz
= 0.04ps (typical)
10k
100k
1M
10M
OFFSET FROM CARRIER FREQUENCY (HZ)
100M
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-
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.
8524AY
www.icst.com/products/hiperclocks.html
6
REV. B AUGUST 1, 2007