Re: generate sin wave with PWM

Jerry Avins wrote:

Paul E. Bennett wrote:
ivan wrote:

hi all,

How do I generate a sin wave using PWM?
The way I have thought is just to create a triangular wave with equal
steps of the PWM duty cycle (depending on freq) and then filter out the
harmonics with a hw filter.
But what if I want to generate a sin wave instead of a triangular wave,
how do I calculate the steps for the duty cycle of the PWM? These steps
are not equal, so I will need to store them in a table.
Any ideas?

Others will tell you of all sorts of formulae and about look-up tables
but one technique that many forget is called a "Digital Differential
Analyser". With some very simple maths and some logic these can be
implemented and produce sine and cosine streams of data which could be
used more-or-less directly by the PWM generation logic.

Put the term "Digital Differential Analyser" and Sizer into Google's
search string and you will get a number of references that may prove
useful (especially if you register for the IEEE and CiteSeer sites.

Paul,

I have long felt that we shared a common way of seeing things. Did you
see my response?

Only after I had posted and on my subsequent trawl through the newsgroups.

--
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