[time-nuts] DDS'ery narrow scoped.

Magnus Danielson magnus at rubidium.dyndns.org
Thu Jul 21 19:30:50 UTC 2011


On 07/21/2011 08:44 PM, Jim Lux wrote:
> On 7/21/11 8:30 AM, Luis Cupido wrote:
>> Magnus,
>> It crossed my mind of messing somehow with the phase
>> accumulator metrics but did not figure a way...
>> that is a good suggestion I will investigate in that direction...
>>
>> (or maybe... if you do have a bit of free time to drop me
>> a couple of lines more, could you please detail
>> a bit more as so far I did not caught the idea clearly enough to start
>> coding...)
>>
>>
>
> You can set up a sine table with any number of entries. Powers of two
> are popular, but, it could be anything..
>
> Say you had multiple tables, one 20 long, one 21 long, one 22 long.
>
> You could use the 20 long one for generating 1/20th of a Hz, the 21 long
> one for generating 1/21th Hz, etc.

That so obvious, we did not consider it a problem. The problem is when 
you need a large variation of N. Using a tuneable scaling to map into a 
suitable length (power of too) would be a better choice. Most FPGAs 
today have hardware multiplier blocks that can do the scaling needed, 
otherwise shift-add scaling (similar to CORDIC) would be a possibility 
as I mentioned in another post.

Cheers,
Magnus



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