[time-nuts] DDS - Cosine v. Sine LUT

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The cordic needs to compute both sin and cos. You are right that you just need one or the other if you have one DAC. 

-----Original Message-----
From: Chris Albertson <albertson.chris at gmail.com>
Sender: time-nuts-bounces at febo.com
Date: Tue, 21 Jun 2011 11:38:30 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT

On Tue, Jun 21, 2011 at 10:44 AM, KD0GLS <kd0gls at mninter.net> wrote:

> Given a complete DDS chip with a single output channel (e.g. AD9834, AD9835), why would one device favor a cosine LUT versus a sine LUT?

Are the LUTs really different?  Ages ago when I made something like
this I used only 90 degrees of the table. That is all you need.  The
other 270 degrees can be made by flipping or inverting.  I assume that
what's stored is neither.  It is data that needs to be interpeted
based on the current quadrant.  But the author might choose to call it
which ever makes the most sense.

-- 

Chris Albertson
Redondo Beach, California

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