Oscillator idea come's unstuck

[Rene Schmitz]

At 02:31 16.01.99 -0000, you wrote:
>Just before christmas a few of us discussed an idea of mine to use analogue
>switches to change the polarity of a cap in an oscillator circuit instead of
>discharging the cap - to allow a glitch free triangle wave, and to remove
>the problems of using a reset circuit.
>
>I built a simple proto-type before christmas, which I have now added an expo
>convertor to, to try out with a keyboard cv.
>Unfortunately, I can't get the oscillator to scale over more than an octave.
>As far as I can see there is nothing wrong with the expo current source, so
>I must assume that the analogue switches (4066) in the discharge path of the
>capacitor are affecting the current in some way...
>I don't know exactly what's going inside the 4066 so I can't really tell if
>the problem is solvable, but it looks like the idea is no use for a musical
>vco.
>
>Oh well, it makes a good LFO at least...
>
>Colin f
>

I don't want to discourage anyone, but either its that the two switches are
conducting simultaneously. (as Jürgen said)
But I suspect another thing: I've read in Horowitz & Hill Chapter 3.12
"Limitations of FET switches", that some (and they mention the 4066) analog
switches have the nasty property to short (!) the input to ground
momentarily. 
If that might happen, then the charge would leak to ground.
I would try it with a 4016 which is different to 4066.

Apart from this it might could be that the R(on) of the switch varies with
the voltage on its inputs. The 4066 is better in this regard than the 4016. 

Bye
 Rene



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