Variable ramp generator

[Martin Czech]

:::First of all I need a variable ramp waveform, i.e. a waveform,
:::whereby the ratio of the rising edge to the falling one is
:::freely adjustable without affecting the frequency. 

This is am adjsutable  tri/saw shaper, right?

My basic idea was to use two inverted sawtooths, no it was Don Tillmann
who came up with the idea. One would have variable gain, the maximum
was taken as output. This way one slope would be adjustable. This way
the frequency would stay constant in any case with the cost of variable
amplitude.  The next idea was of course variable gain for both waves.
I realized that:

1. a real steep saw is unrealizeable 
2. one needs a complicated diode (or other) function network that controls
   the gain stages, the function is not too bad, similar to 1/x
3. Not much is gained compared with a PWM pulse wave/LPF

This is one of the typical cases where you do some nice math,
and end up with a rather uninteresting result.

So, it is possible, but you have temperature and offset problems
(otas,network), so the engineering cost is high, but the audio thrill
is low.  Bad ratio again.

But this is only true for audio purposes. Such a shaper is nice for lfo
modulation, some realy crazy modulations can be done while shaping from
tri to ramp.  Some digital machines gave such a lfo.

I have now a function generator with a Maxim  083 VCO chip, this part
is expensive and it can do this shaping with voltage control, again
with limitations.

If voltage control is not needed, there is a simple potentiometer
circuit for tri/ramp shaping.

m.c.

----------------------------------------------------------------------
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