EMI reduction with jittered clock

[ljy4468]

Hi all,
I've a question about EMI.
For reducing EMI, we can add jitter to clock (spread spectrum).

There are many articles about what's done with jittered signal.

But now I have a question.
How jittered clock signal(spread spectrum) makes EMI lower????
What's the principle?

Someone shows me related article or website??

Thanks in advance.
Regards.

 

[padmanabhamh]

Hi,
I got following information from web please check weather it can be useful to you or not.

The invention claimed is:

1. A method of adding jitter to a clock signal comprising: delaying successive cycles of the clock signal by a cyclically changing amount; and cyclically changing the amount of delay by a plurality of unit delay increments, wherein said cyclically changing comprises controlling amplitude of the cyclically changing amount of delay by selecting a maximum number of the plurality of unit delay increments to cyclically change the amount of delay.

2. The method defined in claim 1 wherein the cyclically changing comprises: controlling frequency of the cyclically changing amount of delay.

3. The method defined in claim 2 wherein the controlling frequency is at least partly responsive to frequency of the clock signal.

4. The method defined in claim 2 wherein controlling the frequency comprises: selecting a rate for cyclically changing the amount of delay by the plurality of unit delay increments.

5. The method defined in claim 3 wherein the controlling frequency comprises: dividing the frequency of the clock signal by a divisor parameter.

6. The method defined in claim 5 wherein the divisor parameter is variable.

7. The method defined in claim 1 wherein the controlling amplitude is at least partly responsive to an amplitude parameter.

8. The method defined in claim 7 wherein the amplitude parameter is variable.

9. Apparatus for adding jitter to a clock signal comprising: means for delaying successive cycles of the clock signal by a cyclically changing amount; and means for cyclically changing the amount of delay by a plurality of unit delay increments, wherein said means for cyclically changing comprises means for controlling amplitude of the cyclically changing amount of delay by means for selecting a maximum number of the plurality of unit delay increments to cyclically change the amount of delay.

10. The apparatus defined in claim 9 wherein the means for cyclically changing comprises: means for controlling frequency of the cyclically changing amount of delay.

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