> 2) There is a novel PWM D/A that works surprisingly well although 12
>    bits might be pushing the envelop. Use a random number generator
>    that is random over the desired digital range. To generate a analog
>    output generate a random number and compare it to the desired
>    output number. If the random number is less than the desired number
>    output a 1 otherwise output a 0 to an output pin. Feed the output
>    pin through a low pass filter. Do this whenever possible in your
>    code. It's advantage is that the code is asynchronous , waiting
>    for a keystroke in a timer interrupt or a idle wait loop. I have
>    used this in a DTMF dialer generating an analog complex wave form
>    within CCTIT standards with only a non critical resistor and
>    small filter cap.

This is a long description for dithering with white noise.  The problem with
this method is that there is no guarantee on the lower bounds of the
frequency content.  It is therefore impossible to guarantee response time or
to design a filter that guarantees a minimum signal to noise ratio.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olin@embedinc.com, http://www.embedinc.com

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