Another Triangle VCO Idea

[Harry Bissell]

Hi Jim:

doing it with current sinks is a twist on an old National Semi Triangle VCO
method
AN74 fig. 17 for one example.   If there is a hidden weenie in this I don't
know what
it is... the resistor fed version here does not work super well, but your
current control
should fix those problems...

H^)  harry

sssh... we are hunting 'ground loops'

patchell wrote:

>     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!
> ------------------------------------------------