Capacitor reset with FET/analogue switch

Don Tillman don at
Sat Mar 16 20:49:04 CET 1996

   Date: Sat, 16 Mar 1996 16:39:12 +0100
   From: Rick Jansen <rick at>

   In sawtooth VCO designs usually a capacitor is charged
   with a current, and reset with an analogue switch of 
   some kind (an old discussion ;-).

Name one.  (I'm serious; I don't know of any actual proven designs of
full audio range sawtooth VCOs that use an analog switch to discharge
the cap.) 

Typically a single bipolar transistor, which is very well suited to
this sort of thing, is used.  A powerFET would be even better.

   I still haven't figured out all the ins and outs of the
   reset process, particularly wether a FET or MOS-switch
   in the form of a HC4066 ic is suitable or not. Theoretically
   ir is not.


  -- don

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