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Why we use high resolution accumulator in Xilinx DDS (NCO)?

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alzomor

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how to use xilinx dds

Hi

My question is about the Xilinx DDS
you can find it's details in this link
https://www.xilinx.com/support/documentation/ip_documentation/dds_ds558.pdf
my question is:
A hi resolution phase accumulator is used and then the phase is Quantized to low resolution before using it for the sine look up table,
Why We use high resolution Accumulator and then quantize it to low resolution?
why don't use a low resolution accumulator?


Salam
Hossam Alzomor
www()i-g()org
 

dds+xilinx+output

A high resolution accumulator gives you very precise frequency control. A low resolution accumulator would give you coarse frequency steps.

The low resolution output to the sine ROM lets you use a relatively small inexpensive ROM, such as a Block RAM.
 
Re: Xilinx DDS (NCO)

Thanks echo47

Your answer is clear ,
but to rephrase my question
Didn't we lose the high resolution of the high resolution accumulator- which gives us very precise frequency control- when we quantize it down to low resolution output after the quantizer?

as the quantizer output is what's used to address the lookup table?

Salam
Hossam Alzomor
www()i-g()org
 

Xilinx DDS (NCO)

You still get the same very precise frequency control even if you connect only some of the phase accumulator bits to the sine ROM. The phase accumulation process determines the frequency, and that's unaffected by how many of its bits you connect to the sine ROM.
 

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    alzomor

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