>
> Having read James post, I understand what you are are getting at. However,
> I still think this is simply a semantics problem. Firstly, it is
> unequivocally a form of DAC. It converts a digital value to an analog one.
> In this case the DAC is a delta sigma converter, which was invented by
> Philips in the 60's (have a look at
>
http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html )
>
> James is quite correct that with equal value resistors, two of the states
> are different to the rest in that they output a voltage which is not either
> Vcc or ground, and in the context of charging a capacitor this obviously
> makes a difference to the end point voltage.
>
> However, using trinary weighted resitors and you have a classic DAC.
> Integrate the output of this and you can generate arbitrary slopes. The
> essential difference is that the orignal design has a current output so a
> capacitor can be charged directly. With the trinary weighted resistors the
> DAC has a voltage output, so an active integrator would need to be used.
>
> Whilst Romans implementation may be novel, at the end of the day it's simply
> a low bit rate, low resolution digital audio system, and suffers from the
> same problems as any such system, i.e. limited bandwidth and high harmonic
> distortion. The sample rate still has to be significantly higher than the
> maximum frequency of interest, as with any system
>
> As Roman himself states "it is basic encoding methodology, just done in a
> clever way to make it very easy and fast on a PIC."
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