NBC12430 datasheet(13/18 Pages) ONSEMI

13 / 18 page

NBC12430, NBC12430A

http://onsemi.com

There are different ways to measure jitter and often they

are confused with one another. The typical 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,

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.

Recent hardware and software developments have

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.

M1 by Amherst was used as well and both test methods

correlated.

This test process can be correlated to earlier test methods

and is more accurate. All of the jitter data reported on the

NBC12430 and NBC12430A was collected in this manner.

Figure 12 shows the jitter as a function of the output

frequency. The graph shows that for output frequencies from

50 to 800 MHz the jitter falls within the

"20 ps

peak−to−peak specification. The general trend is that as the

output frequency is increased, the output edge jitter will

decrease.

Figure 11 illustrates the RMS jitter performance of the

NBC12430 and NBC12430A across its specified VCO

frequency range. Note that 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. The

data presented has not been compensated for trigger jitter.

Long−Term Period Jitter is the maximum jitter

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.

The NBC12430 and NBC12430A exhibit long term and

cycle−to−cycle 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.

Figure 11. RMS Jitter vs. VCO Frequency

VCO FREQUENCY (MHz)

400

500

600

700

800

N = 1

N = 8

N = 2

N = 4

Figure 12. RMS Jitter vs. Output Frequency

800

700

600

500

400

300

200

100

OUTPUT FREQUENCY (MHz)

NBC12430 Datasheet(PDF) 13 Page - ON Semiconductor

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