antilog

[Fraser, Colin J]

> -----Original Message-----
> From: Paul Perry [mailto:pfperry at melbpc.org.au]
> Sent: 10 August 2000 12:29
> To: synth-diy at node12b53.a2000.nl
> Subject: Re: antilog
> 
> I've been interested for a while in the possibility of making 
> an exponential
> convertor 
> using a micro, and multiplexing it, so that all the problems 
> of stability in
> the 
> expo cells would be a thing of the past.
> But, i'm not a programmer.
> I know 12 bits would be enough, though 16 bit serial D to A 
> convertors are
> cheapest.
> (Though not guaranteed for DC, I have never had trouble with them).

I used a 12 bit convertor and a lookup table to provide expo outputs on a cv
convertor.
This is only really suitable for discrete steps (ie midi notes) without a
really high resolution DAC.
Even with a hi res DAC you'll still probably have an easier time using an
analogue expo convertor than getting rid of the artefacts of a digital
implementation if you want to use expo FM.

The LM13600 temperature compensation scheme looks really smart and might be
the answer.
How come nobody noticed it hidden away at the end of the data sheet all
these years ?
And why on earth does the data sheet suggest using a fully temperature
compensated expo convertor to control the stereo volume control, rather than
the tri-square oscillator also shown on the data sheet ?

Colin f