Switching Capacitor VCO (Re: Osc reset time)

[Mikko Helin]

Interesting, could this be used on ASM-1/EN/TM type VCO in this way
(curren sink not shown, sorry for the quality):
 
 http://www.uta.fi/~helin/scvco.gif

I think this could give output voltage from -5V to +5V, the exponential
converter should work like on original VCO design (I think).

BTW. Are the CA3240 (dual) opamps similar to 3140, or can they
source more current?

-Mikko

>This idea is very interesting.  Essentially, zero-current switching of the
>integrating capacitor?  Can you put up a sketch?
>
>-Art
>
>-----Original Message-----
>From: Fraser, Colin J <Colin.Fraser at scottishpower.plc.uk>
>To: 'synth-diy at mailhost.bpa.nl' <synth-diy at mailhost.bpa.nl>
>Date: Wednesday, December 16, 1998 8:48 AM
>Subject: Osc reset time
>
>
>Thinking about using analogue switches to reset the cap in a saw wave core,
>it occurs to me that it should be possible to use analogue switches so that
>the capacitor does not need to be discharged to be 'reset'.
>
>If you have a dual two-way analogue switch, with very low on resistance, you
>could connect the capacitor so that you can reverse its polarity in the
>circuit - ie a comparator detects the peak level and toggles the switches so
>that the connections from the cap to the ref voltage and the current source
>are swapped. At the next peak, they are swapped back. This should give near
>instant reset times.
>I would expect this has been done before if it's workable.
>Is this likely to have any advantage over discharging the cap ?
>Disadvantages ?
>
>
>Colin f
>
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