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參數(shù)資料
| 型號： | FS782BZB |
| 英文描述： | MISCELLANEOUS CLOCK GENERATOR|SOP|8PIN|PLASTIC |
| 中文描述： | 雜項時鐘發(fā)生器|?？苵 8引腳|塑料 |
| 文件頁數(shù)： | 8/13頁 |
| 文件大?。?/td> | 103K |
| 代理商： | FS782BZB |
LOW EMI SPECTRUM SPREAD CLOCK
Cypress Semiconductor Corporation
525 Los Coches St.
Milpitas, CA 95035. Tel: 408-263-6300, Fax: 408-263-6571
http://www.cypress.com
Document#: 38-07029 Rev. **
05/07/2001
Page 8 of 13
APPROVED
PRODUCT
FS781/82/84
SSCG Modulation Profile
The digital control inputs S0 and S1 determine the modulation frequency of FS781/2/4 products. The input
frequency is divided by a fixed number, depending on the operating range that is selected. The modulation
frequency of the FS78x can be determined from the Table 8. To compute the modulation frequency enter to Table
8 with selected S0 and S1 values to obtain Modulation Divider Number, and divide the input frequency by this fix
number.
S1
S0
Input Frequency
Range (MHz)
6 to 16
16 to 32
32 to 66
66 to 82
Modulation
Divider Number
120
240
480
720
0
0
1
1
0
1
0
1
Table 9
Figure 5. Frequency Profile in Time Domain
With the correct loop filter connected to pin 4, the following profile will provide the best EMI reduction. This profile
can be seen on a Time Domain Analyzer.
Theory of Operation
The FS781/2/4 devices are Phase Lock Loop (PLL) type clock generators using Direct Digital Synthesis (DDS).
By precisely controlling the bandwidth of the output clock, the FS781/2/4 products become a Low EMI clock
generator. The theory and detailed operation of these products will be discussed in the following sections.
EMI
All clocks generate unwanted energy in their harmonics. Conventional digital clocks are square waves with a duty
cycle that is very close to 50 %. Because of the 50/50 duty cycle, digital clocks generate most of their harmonic
energy in the odd harmonics, i.e.; 3
rd
, 5
th
, 7
th
etc. It is possible to reduce the amount of energy contained in the
fundamental and harmonics by increasing the bandwidth of the fundamental clock frequency. Conventional digital
Xin
+ .5%
- .5%
TIME (microseconds)
1.0%
Total
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
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| FS786BZB | 制造商:IMI 功能描述: |
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