[sdiy] TZ triangle core

[nicolas]

One of the fairly standard triangle core approaches is to do something similar to this, but with the switcher and the integrator combined around a single opamp.  So I guess the difference you are proposing is to split those and make the integrator with an OTA to give you a multiply option?  Sounds like it will work fine.  The only reason you will get voltages slightly outside the schmitt trigger limits is due to slow switching times vs high oscillator frequencies if you use an ordinary opamp as your comparator.

Cheers,
Nicolas


--- On Mon, 28/2/11, Ian Fritz <ijfritz at comcast.net> wrote:

> From: Ian Fritz <ijfritz at comcast.net>
> Subject: [sdiy] (no subject)
> To: synth-diy at dropmix.xs4all.nl
> Received: Monday, 28 February, 2011, 10:38 AM
> Hello --
> 
> My latest chaos system uses a thru-zero FM VCO to generate
> traveling wave signals. (Posted previously. Also see the
> thread on e-m.)  So I'm thinking about how to make a
> simple sort of auxilliary TZ oscillator for this
> function.  Here's an idea I've come up with, and
> looking around I don't see anything similar already done.
> 
> The oscillator consists of a signal polarity switcher, a
> bipolar integrator and a Schmidt trigger all connected in a
> loop.
> 
> The switcher is the familiar circuit with an opamp, three
> R's and an FET.  It's often used in VCO
> waveshapers.  The input signal feeds this
> circuit.  The switcher drives a multiplying integrator,
> just an OTA driving a cap to ground. The switcher goes to
> the OTA's bipolar input and the other input just needs a
> DC  bias current for my application. (In general, it
> could have the usual exponential current control, or a
> linear, unipolar modulation source.) The opamp Schmidt
> trigger reverses the polarity of the input whenever the
> signal reaches +/- 5V, causing the ramp to reverse
> direction.  So the whole thing would be just two opamps
> and an OTA.
> 
> Anyone see a reason why this wouldn't work?  I'm a bit
> worried about the signal escaping the +/-5V range, but a
> clamp at slightly above this level should allow the signal
> to get back to normal reasonably quickly.  Has anyone
> seen a TZ FM VCO done this way?  Seems pretty simple,
> at least conceptually.
> 
> Ian 
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