NBC12439 ON, NBC12439 Datasheet - Page 14

• Manufacturer Part Number: NBC12439
• Description: 3.3 V/5 V Programmable PLL Synthesized Clock Generator
• Manufacturer: ON

Jitter Performance of the NBC12439
generation and distribution. Clock jitter can be defined as the
deviation in a clock’s output transition from its ideal
position.
variation between adjacent periods over a defined number of
observed cycles. The number of cycles observed is
application dependent but the JEDEC specification is 1000
cycles. See Figure 9.
the highest and lowest acquired value and is represented as
the width of the Gaussian base. See Figure 10.
are confused with one another. An earlier method of
measuring jitter is to look at the timing signal with an
oscilloscope and observe the variations in period-to-period
or cycle-to-cycle. If the scope is set up to trigger on every
rising or falling edge, set to infinite persistence mode and
allowed to trace sufficient cycles, it is possible to determine
the maximum and minimum periods of the timing signal.
Digital scopes can accumulate a large number of cycles,
Jitter is a common parameter associated with clock
Cycle-to-Cycle
Random Peak-to-Peak Jitter is the difference between
There are different ways to measure jitter and often they
Figure 10. Random Peak-to-Peak and RMS Jitter
*1,000 - 10,000 Cycles
Figure 9. Cycle-to-Cycle Jitter
T
0
Time*
T
JITTER(cycle- cycle)
Jitter (short-term) is the period
= T
T
1
1
- T
Typical
Gaussian
Distribution
0
RMS
or one
Sigma
Jitter
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NBC12439
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create a histogram of the edge placements and record
peak-to-peak as well as standard deviations of the jitter.
Care must be taken that the measured edge is the edge
immediately following the trigger edge. These scopes can
also store a finite number of period durations and
post-processing software can analyze the data to find the
maximum and minimum periods.
resulted in advanced jitter measurement techniques. The
Tektronix TDS-series oscilloscopes have superb jitter
analysis capabilities on non-contiguous clocks with their
histogram and statistics capabilities. The Tektronix
TDSJIT2/3 Jitter Analysis software provides many key
timing parameter measurements and will extend that
capability by making jitter measurements on contiguous
clock and data cycles from single-shot acquisitions.
correlated.
methods and are more accurate. All of the jitter data reported
on the NBC12439 was collected in this manner. Figure 11
shows the RMS jitter performance as a function of the VCO
frequency range. The general trend is that as the VCO
frequency is increased, the RMS output jitter will decrease.
the output frequency. Note the jitter is a function of both the
output frequency as well as the VCO frequency. However,
the VCO frequency shows a much stronger dependence.
observed at the end of a period’s edge when compared to the
position of the perfect reference clock’s edge and is specified
by the number of cycles over which the jitter is measured.
The number of cycles used to look for the maximum jitter
varies by application but the JEDEC spec is 10,000 observed
cycles.
jitter, which rivals that of SAW based oscillators. This jitter
performance comes with the added flexibility associated
with a synthesizer over a fixed frequency oscillator. The
jitter data presented should provide users with enough
information to determine the effect on their overall timing
budget. The jitter performance meets the needs of most
system designs while adding the flexibility of frequency
margining and field upgrades. These features are not
available with a fixed frequency SAW oscillator.
Recent hardware and software developments have
M1 by Amherst was used as well and both test methods
These test processes can be correlated to earlier test
Figure 12 illustrates the RMS jitter performance versus
Long-Term Period Jitter is the maximum jitter
The NBC12439 exhibits long term and cycle-to-cycle