MAXIM MAX038 Osc.

[Martin Czech]

Has anybody made experiences with the MAXIM MAX083 Function Generator Chip ?

http://www.maxim-ic.com/Counters.html

This Device offers the wellknown triangle generator circuit and approx.
sine and pulse wave as well, but it has only one output (grumble..).
You can choose the waveform with two digital mux select inputs.
The frequency range is from 0 to some 10MHz and the signals looks quite 
good, even at the high frequency edge.

All this is not very thrilling, but :

The chip has an unique feature. It offers voltage controlled symmetry.
Thus you can shift the triangle wave near to a falling or rising sawtoth,
without shifting the frequency.
This may not be suitable for audio things, since it introduces some frequency error
but it is quite interesting for LFOs etc. (Think of Waldorf's Microwave LFOs.
But they are "software"). 
I could imagine some very interesting modulation
patterns with this feature. 

The old EMS synthies also had such an idea, but in the audio osc.

This question is for all the EEs out there :

How the ... do they do it ?

I know,
Tektronix use a pot adjustable symmetry circuit for their oscs (which is described e.g. in
"Tietze-Schenk Halbleiterschaltungstechnik ISBN 3 540 09848 8" 5. edition chapter 18.4.2).
But this is a potentiometer circuit with "hand control" rather than voltage control.
If you follow the explanation in this text you`ll find out that some nasty diode
function network (f(x)=x/(1-x)) will be needed to shift symmetry by control voltage without 
frequency
change. So you get awfull temperature stability problems. I don't think that this is the
circuit idea in the MAX038.

So again : How the ... do they do it ?


Sorry for wasting so much bandwith.

m.c.