AVR-Chat

thanks... I wasn't aware of these.

 - jim

On Mon, 5 Dec 2005 23:38:01 +0200
"MuRaT KaRaDeNiZ" <karademu.yahoogroups@onlinefavbar.com> wrote:

> Hello,
> 
> There are other choices:
> Check the avr tiny series. There are devices with special high speed pwm
> peripherals. These micro(s) (I dont remember exact part number) have a
> pll clock multiplier built in, just to generate high clock frequency for
> this demanding 
> peripherals, you get 100khz and more easily.
> 
> And there are the at90pwm2, at90pwm3 devices, they have >1mhz DAC
> built-in. (beside complex high speed pwm peripherals). I will use these
> devices in a few weeks in my thesis project.
> 
> 
> 
> Regards.
> 
> Murat Karadeniz
> http://www.onlinefavbar.com/mukas
> 
> 
> 
> 
> -----Original Message-----
> From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
> Behalf Of Jim Wagner
> Sent: Monday, December 05, 2005 10:09 PM
> To: AVR-Chat@yahoogroups.com
> Subject: Re: [AVR-Chat] Generating sine waves with PWM
> 
> 
> I'm working on a project with similar constraints (even
> uses 2200Hz as one of the tones). There are not very many
> ways to improve things. 
> 
> I am using an 6-bt R-2R DAC driven by six port pins. Since
> the DAC output only has small steps in it, the harmonic
> content is much lower and the rate and filtering are much
> less demanding.
> 
> You can add a smoothing filter with more sections (poles).
> I am actually using a 6-pole switched-capacitor filter that
> is "tuned" according to an external clock (also provided by
> the micro). A good filter like this can do wonders. With
> such a small number of samples (points) per cycle, a simple 2-pole
> active filter just won't hack it.
> 
> You can decrease the TOP value (that is, reduce the number
> of bits) so that the PWM period is shorter and you can get
> more of them in per tone cycle. With such few samples, it
> makes little sense to try for a full 8-bits. Every halving
> of TOP (from the standard value of 255) drops one
> resolution bit and doubles the repetion frequency of the
> PWM, doubling the number of samples per tone cycle.
> 
> Use the fastest possible main clock (that is, highest
> frequency crystal). This will give you the fastest possible
> PWM clock and that will give the highest possible PWM repetition rate. 
> 
> Not many other choices than these! That is why I chose not
> to use PWM for this kind of application.
> 
> Jim Wagner
> 
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