Another Triangle VCO Idea

[Jim Patchell]

    I am going to have to look in the archives.  I must be getting
senile.....:-)

    I am going to try to draw up the circuit and post it tonight.

    -Jim

Ian Fritz wrote:

> Hi Jim --
>
> Just of the top of the head, it sounds like a reasonable idea. It reminds me
> a bit of the charge-pump circuit that was being discussed here this week, in
> the sense that the control current is on all the time and the "pump" current
> is only on during the down ramp.
>
>   Ian
>
> ----- Original Message -----
> From: "patchell" <patchell at silcom.com>
> To: <synth-diy at node12b53.a2000.nl>
> Sent: Tuesday, September 26, 2000 9:32 PM
> Subject: Another Triangle VCO Idea
>
> >     Well, if this isn't a new idea, well, what can I say (I seriously
> > doubt there are any new ideas).
> >
> >     Anyway.  So far, I have built two different triangle oscilators.
> > The first one used a "ota" current switch (nothing new here).  The
> > second one was similar to one of  Ian Fritz's oscilators that used a
> > pair of fet switches and a current mirror (I used JFETs).  Here is my
> > idea for another one:
> >
> >     The exponential converter would have two identical current sinks.
> > One would go to the input of an opamp integrator (in the usual way), the
> > second will go to a current mirror.  The current mirror would be set up
> > to source twice the current of the exponential converter.  Also, the
> > current mirror would be set up so that it could be turned on and off.
> >     So, when the current mirror is off, the current sink would suck
> > current out of the integrator, making the output voltage ramp up.  When
> > it gets to a threshold, the current mirror would be turned on.  Since it
> > is sourcing twice the current as the sink, the result is that the same
> > amount of current is now being sourced into the integrator, as was being
> > sunk before.  This will cause the voltage to ramp down at the same rate.
> >
> >     Don't know if I will be able to try this this weekend.  If anybody
> > else can follow what I said, I would be interested in the results.  Or,
> > is this just a bad dream?
> >
> > --
> >  -Jim
> > ------------------------------------------------
> > * Visit:http://www.silcom.com/~patchell/
> > *-----------------------------------------------
> > *If you didn't buy a home in Santa Barbara,
> > * You didn't pay enough!
> > ------------------------------------------------
> >
> >
> >