CDCE62005 Datasheet, PDF(69/76 Page) Texas Instruments – Five/Ten Output Clock Generator/Jitter Cleaner With Integrated Dual VCOs

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CDCE62005 Datasheet, PDF (69/76 Pages) Texas Instruments – Five/Ten Output Clock Generator/Jitter Cleaner With Integrated Dual VCOs

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CDCE62005

www.ti.com........................................................................................................................................................................................... SCAS862 â NOVEMBER 2008

30.72 MHz

10.00 MHz

/1:/2:HiZ

Reference

Divider

Output

Divider 0

Output

Divider 1

122 .88 MHz

491 .52 MHz

Input

Divider

Feedback

Divider

PFD/

Prescaler

Output

Divider 2

Output

Divider 3

245 .76 MHz

30.72 MHz

Output

Divider 4

10 MHz

Figure 43. CDCE62005 Jitter Cleaner Example

Clocking ADCs with the CDCE62005

High-speed analog to digital converters incorporate high input bandwidth on both the analog port and the sample

clock port. Often the input bandwidth far exceeds the sample rate of the converter. Engineers regularly

implement receiver chains that take advantage of the characteristics of bandpass sampling. This implementation

trend often causes engineers working in communications system design to encounter the term clock limited

performance. Therefore, it is important to understand the impact of clock jitter on ADC performance. Equation 8

shows the relationship of data converter signal to noise ratio (SNR) to total jitter.

SNR jitter

20 log10

Ã©

Ãª

Ã¹

Ãº

Ã« 2Ïfin jittertotal Ã»

(8)

Total jitter comprises two components: the intrinsic aperture jitter of the converter and the jitter of the sample

clock:

jittertotal = (jitterADC )2 + (jitterCLK )2

(9)

With respect to an ADC with N-bits of resolution, ignoring total jitter, DNL, and input noise, the following equation

shows the relationship between resolution and SNR:

SNRADC = 6.02N +1.76

(10)

Figure 44 plots Equation 8 and Equation 10 for constant values of total jitter. When used in conjunction with most

ADCs, the CDCE62005 supports a total jitter performance value of <1 ps.

Product Folder Link(s) :CDCE62005

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