8413S12I-100_16 Datasheet, PDF (15/33 Pages) Integrated Device Technology – Clock Generator for Cavium Processors

8413S12I-100 Data Sheet
Peak-to-Peak Jitter Calculations
A standard deviation of a statistical population or data set is the
square root of its variance. A standard deviation is used to calcu-
late the probability of an anomaly or to predict a failure. Many
times, the term "root mean square" (RMS) is used synonymously
for standard deviation. This is accurate when referring to the
square root of the mean squared deviation of a signal from a given
baseline and when the data set contains a Gaussian distribution
with no deterministic components. A low standard deviation indi-
cates that the data set is close to the mean with little variation. A
large standard deviation indicates that the data set is spread out
and has a large variation from the mean.
A standard deviation is required when calculating peak-to-peak
jitter. Since true peak-to-peak jitter is random and unbounded, it is
important to always associate a bit error ratio (BER) when specify-
ing a peak-to-peak jitter limit. Without it, the specification does not
have a boundary and will continue get larger with sample size.
Given that a BER is application specific, many frequency timing
devices specify jitter as an RMS. This allows the peak-to-peak
jitter to be calculated for the specific application and BER require-
ment. Because a standard deviation is the variation from the mean
of the data set, it is important to always calculate the peak-to-peak
jitter using the typical RMS value.
The table shows the BER with its appropriate RMS Multiplier.
There are two columns for the RMS multiplier, one should be used
if your signal is data and the other should be used if the signal is a
repetitive clock signal. The difference between the two is the data
transition density (DTD). The DTD is the number of rising or falling
transitions divided by the total number of bits. For a clock signal,
they are equal, hence the DTD is 1. For Data, on average, most
common encoding standards have a.5 DTD.
Once the BER is chosen, there are two circumstances to consider.
Is the data set purely Gaussian or does it contains any determinis-
tic component? If it is Gaussian, then the peak to peak jitter can
be calculated by simply multiplying the RMS multiplier with the
typical RMS specification. For example, if a 10^-12 BER is required
for a clock signal, multiply 14.260 times the typical jitter specifica-
tion.
Jitter (Peak to Peak) = RMS Multiplier x RMS (typical)
If the data set contains deterministic components, then the
Random Jitter (R_J) and Deterministic Jitter (D_J) must be separated
and analyzed separately. RJ, also know as Gaussian Jitter, is not
bounded and the peak-to-peak will continue to get larger as the
sample size increases. Alternatively, peak-to-peak value of D_J is
bounded an can easily be observed and predicted. Therefore, the
peak-to-peak jitter for the random component must be added to
the deterministic component. this is call Total Jitter (T_J).
Total Jitter (Peak to Peak) = [RMS Multiplier x Random Jitter (R_J)] +
Deterministic Jitter (D_J)
This calculation is not specific to one type of jitter classification. It
can be used to calculate BER on various types of RMS jitter. It is
important that the user understands their jitter requirement to
ensure they are calculating the correct BER for their jitter require-
ment.
Table 8. BER Table
BER
RMS Multiplier Data,
“DTD = 0.5”
10^-3
6.180
10^-4
7.438
10^-5
8.530
10^-6
9.507
10^-7
10.399
10^-8
11.224
10^-9
10^-10
10^-11
11.996
12.723
13.412
10^-12
14.069
10^-13
14.698
10^-14
10^-15
15.301
15.883
RMS Multiplier Clock,
“DTD = 1”
6.582
7.782
8.834
9.784
10.654
11.462
12.218
12.934
13.614
14.260
14.882
15.478
16.028
NOTE: Use R_J and D_J values for AC Characteristics Tables 7C to
calculate T_J.
©2016 Integrated Device Technology, Inc.
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October 4, 2016