[hpsdr] synthesizers.

[Naylor Jonathan]

> As I didn't know until now what a CORDIC was and searched the Email
> archives
> at hpsdr.com, but didn't find an explanation of it, I searched the
> internet
> and found a nice one at:
> 
> http://www.dspguru.com/info/faqs/cordic.htm
> 
> 
> Cool!!!

Another way to visualise CORDIC and the one that makes much more sense
to me is to use the trigonometric identities for sin(A + B) and cos(A +
B), and then you'll see that the mysterious sets of sin's and cosine's
make a lot more sense, and that the equivalent of sin B and cos B is a
fixed value, based on the increment value B. The results of the
previous calculation of sin(A + B) and cos(A + B) are fed into the next
calculation as the values of sin A and cos A. The seed values of sin A
and cos A being 0.0 and 1.0 respectively.

I worked out how CORDIC worked that way, long before I knew the name
CORDIC, and from my knowledge of the above identities. It was something
that I'd done many weeks of at school for my A levels over 20 years
ago.

It's a great technique and beautifully obvious too. The only caveat
being that enough bits are used to store the values so the rounding
errors don't accumulate too quickly. A standard Intel 32-bit floating
point value is adequate.

Jonathan  W9/G4KLX



 
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