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From: john larkin <JL@gct.com>
Newsgroups: sci.electronics.design
Subject: Re: DDS, again
Date: Fri, 13 Dec 2024 09:09:57 -0800
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On Fri, 13 Dec 2024 21:17:13 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

>On 11/12/2024 9:31 pm, john larkin wrote:
>> The "RF" mindset, that one has to do the sine and dac and hi-rent
>> lowpass filter and comparator, is not only a bunch of work and
>> expense, it gets really nasty at low frequencies.
>
>Then don't do it at low frequencies. Do it at 2^N times the low 
>frequency that you want, and then after the comparator divide by 2^N.

I think that can be done, but very carefully. We need long-term phase
coherence to simulate a complex geared machine, and we need frequency
changes to happen at a selected phase angle, like top-dead-center of
some waveform of some part of a mechanism.

Using the MSB of the phase accumulator is sure appealing. Going
off-chip to a DAC and a filter and a comparator adds time lag and
jitter.

Most DDSs are RF oriented so don't care about time. Maybe some exotic
radars would.