MC12429FN 查看數據表（PDF） - Motorola => Freescale

零件编号

产品描述 (功能)

生产厂家

MC12429FN

High Frequency Clock Generator

Motorola => Freescale 

MC12429

be applications in which overall performance is being

degraded due to system power supply noise. The power

supply filter and bypass schemes discussed in this section

should be adequate to eliminate power supply noise related

problems in most designs.

Jitter Performance of the MC12429

The MC12429 exhibits long term and cycle–to–cycle jitter

which rivals that of SAW based oscillators. This jitter

performance comes with the added flexibility one gets with a

synthesizer over a fixed frequency oscillator.

25

N=2

20

N=4

N=8

15

N=16

10

5

0

400

500

600

700

800

VCO Frequency (MHz)

Figure 7. RMS PLL Jitter versus VCO Frequency

Figure 7 illustrates the RMS jitter performance of the

MC12429 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, this fact provides a

measure of guardband to the reported data. In addition the

data represents long term period jitter, the cycle–to–cycle

jitter could not be measured to the level of accuracy required

with available test equipment but certainly will be smaller

than the long term period jitter.

The most commonly specified jitter parameter is

cycle–to–cycle jitter. Unfortunately with today’s high

performance measurement equipment there is no way to

measure this parameter for jitter performance in the class

demonstrated by the MC12429. As a result different methods

are used which approximate cycle–to–cycle jitter. The typical

method of measuring the jitter is to 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. The

oscilloscope cannot collect adjacent pulses, rather it collects

pulses from a very large sample of pulses. It is safe to

assume that collecting pulse information in this mode will

produce period jitter values somewhat larger than if

consecutive cycles (cycle–to–cycle jitter) were measured. All

of the jitter data reported on the MC12429 was collected in

this manner.

Figure 8 shows the jitter as a function of the output

frequency. For the 12429 this information is probably of more

importance. The flat line represents an RMS jitter value that

corresponds to an 8 sigma ±25ps peak–to–peak long term

period jitter. The graph shows that for output frequencies

from 87.5 to 400MHz the jitter falls within the ±25ps

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

output frequency is decreased the output edge jitter will

increase.

25

20

15

6.25ps Reference

10

5

0

25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400

Output Frequency (MHz)

Figure 8. RMS Jitter versus Output Frequency

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.

MOTOROLA

8

TIMING SOLUTIONS

BR1333 — Rev 6

Share Link: