[time-nuts] DDS'ery

lists at lazygranch.com lists at lazygranch.com
Tue Jun 21 00:24:27 UTC 2011


I don't have the algorithm in front of me, but I don't recall any multiplication, just addition and magnitude comparison. 
-----Original Message-----
From: Jim Lux <jimlux at earthlink.net>
Sender: time-nuts-bounces at febo.com
Date: Mon, 20 Jun 2011 17:14:44 
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'ery

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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