Integrated
Circuit
Systems, Inc.
ICS83052I
2:1, S
INGLE
-E
NDED
M
ULTIPLEXER
A
DDITIVE
P
HASE
J
ITTER
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
0
-10
-20
-30
-40
-50
-60
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.
Additive Phase Jitter (Random)
at 155.52MHz (12kHz - 20MHz)
= 0.18ps (typical)
SSB P
HASE
N
OISE
dBc/H
Z
-70
-80
-90
-100
-110
-120
-130
-140
-150
-160
-170
-180
-190
1k
10k
100k
1M
10M
100M
O
FFSET
F
ROM
C
ARRIER
F
REQUENCY
(H
Z
)
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
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.
83052AGI
www.icst.com/products/hiperclocks.html
REV. A AUGUST 2, 2005
7
ICS [ INTEGRATED CIRCUIT SYSTEMS ]
