pwm ...

[Kimmo Koli]

On Thu, 14 Nov 1996, Haible_Juergen#Tel2743 wrote:

> 
> > Why use D/A-converters for CV-control ? A 100 kHz variable pulse-width 
> signal
> > (or even better a tri-state signal = double resolution) could be easily
> > generated with software.
> 
> Do you know what precision (jitter!) you'd need top get a 7 or 8 bit
> accurarcy ?? And what amount of HF this would produce ?
> 8-bit DACs are cheap, so why not use them?
> 
> JH.
> 
Well, the linearity and even monotony of a 8-bit D/A-converter is usually 
very poor. Of cource 8-bit D/A-converters are cheap, but are the cheap 
compared to a hex CMOS-buffer and a few resistors and capacitors ? And
the availability of a spesific DAC, old D/A and A/D chips are hard to 
find. I was thinking of a design you could build without any problems 
also in the future.  

If uP clock is tens of megahertz and it has a chrystal clock oscillator, 
jitter is no problem. An PWM is linear, that why CD-players use 1-bit 
D/A-converters. Of cource, the bit stream should not depend on the timing
of the uP-bus.

That's all this time,
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
   Kimmo Koli                         Helsinki University of Technology 
   kimmo at ecdl.hut.fi                  Electronic Circuit Design Laboratory
   http://www.ecdl.hut.fi/~kimmo      Otakaari 5 A 
   Tel:  +358 9 451 2273              FIN-02150 Espoo
   Fax:  +358 9 451 2269              Finland 
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