Implement Phase Dither in DDS

[xie.qiang]

dds dither

Hei Guys,

I am currently working on the AWG project, and I am in charge of the DDS module, we need to Implement Phase Dither after the trunction of accumulator and before the phase-attitude converter in order to increase SFDR.

There are many papers about the spur-decreae by using phase dither like PN sequencial or M sequencial, etc, most of those do not mention how to realization..

I do not know how to find and setup the correct model of hte Phase Dither to simulink DDS system in matlab, further more, I also need to implement the phase dither in FPGA.

So, need you guys to help me..

Thanks very much

 

[FvM]

dds dithering

Hello,

After accumulator truncation, there is nothing to dither! Dithering can be achieved by adding a pseudo random value to accumulator before truncation. Just consider a PN having equal range as the fractional part of accumulator.

I know no particular literature, but I think, operation is obvious an can be derived easily.

Regards,
Frank

 

[xie.qiang]

dds met phase dithering

Hello,

After accumulator truncation, there is nothing to dither! Dithering can be achieved by adding a pseudo random value to accumulator before truncation. Just consider a PN having equal range as the fractional part of accumulator.

I know no particular literature, but I think, operation is obvious an can be derived easily.

Regards,
Frank

thanks, Frank.

Yes, you r right, need to add dither before trunction, but i still can not figure out how to find the correct model for the dither..

 

[FvM]

dither dds

Hello,

I didn't review the respective literature, but if they suggest pseudo random signal, it could be generated by a LFSR with length according to the dither signal word with (= accumulator fractional part). References to LFSR can be surely found in the forum, wikipdedia and anywhere. But cause LFSR are pseudo random, they are also periodical and thus their effect should be checked in simulation.

Regards,
Frank