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s002wjhw
Voyager
Voyager
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Registered: ‎06-26-2015

DDS ip question

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in the DDS .pdf, it mention the DDS can generate waveform up to its CLK So for 200mhz clk, 12bit, it can generate wave upto 200mhz, 76db  But Nyquist indicate Fs/2, so how does DDS generate 200Mhz wave, when its clk/Fs is at 200Mhz?  However, in Xilinx ip doc, it says it can generate from 0 to 200Mhz, even its clk is 200mhz, how is that possible.

 

ok I think the IP map 0.5fs to 1fs into -0.5fs to 0?

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drjohnsmith
Teacher
Teacher
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Registered: ‎07-09-2009

have a search of the forum

 

this has come up a few times,

 

DDS as you say can not generate above 1/2 the clock frequency, unless you use harmonics,

 

 

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drjohnsmith
Teacher
Teacher
1,029 Views
Registered: ‎07-09-2009

have a search of the forum

 

this has come up a few times,

 

DDS as you say can not generate above 1/2 the clock frequency, unless you use harmonics,

 

 

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>

View solution in original post

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jmcclusk
Mentor
Mentor
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Registered: ‎02-24-2014

No, the DDS cannot violate Nyquist sampling.    For a single sine output, a 100 MHz clock will allow generation of a sine wave up to 50 MHz..     For a sine/cosine output,  the range then becomes -50 MHz to +50 MHz (complex data),  which is technically a span of 100 MHz.     But the peak frequency is still half the clock rate.  

Don't forget to close a thread when possible by accepting a post as a solution.
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