[time-nuts] DDS'ery

Jim Lux jimlux at earthlink.net
Tue Jun 21 00:14:44 UTC 2011

On 6/20/11 12:17 PM, lists at lazygranch.com wrote:
> Just a FYI, you don't have to use sine lookup tables. You can generate sine and cosine on the fly with a coordic. Perhaps not easy at RF speed, but very common in audio DSP.

It's a tradeoff..  To do CORDIC you need four multiplies and 2 adds, 
which might be a lot of gates, if you have a fair number of bits, 
compared to an adder and some lookup tables.

If you have a fast multiply instruction on a processor, then CORDIC gets 
very attractive.

The other problem with CORDIC is that roundoff errors accumulate, the 
longer you run the generator for, because it's basically a difference 
equation/numerical integration sort of scheme.

That said, some of AD's latest DDSes use a monolithic CORDIC generator.

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