[sdiy] VCO reset time

[harrybissell]

Hi Don (et al)

I did a simulation of the trapezoid core and it indeed looks very
promising...
but correct me if I'm wrong

The two integrating capacitors have to be the same value (precisely).
When I
simulated one a little bigger/smaller... performance degraded severely.
How will
you get around this issue ???

H^) harry

Don Tillman wrote:

>    > Date: Wed, 02 Jun 2004 21:21:56 +0200
>    > From: Rene_Schmitz <uzs159 at uni-bonn.de>
>    >
>    > > What is a good ramp reset time ?  How fast have you seen
>    > > ramp reset be ?
>    >
>    > Zero. (A special triangle core ;-))
>
>    > Date: Thu, 03 Jun 2004 00:14:30 +0200 (CEST)
>    > From: Magnus Danielson <cfmd at bredband.net>
>    >
>    > I consider triangular cores a very interesting concept and they
>    > might compete very well with sawtooth cores IMHO.
>
> I've been questioning the whole point of sawtooth cores for a couple
> years now, and I'm thinking that triangle cores are a lot better.
>
> Here are three advantages of triangle core VCO's:
>
>   1. No reset detuning.
>
>   2. You can get each of the basic waveforms in just one step:
>
>      triangle -> saw
>               -> square
>               -> sine
>
>      With the sawtooth you need two steps to get to the sine wave (and
>      possibly the square wave depending upon how you want PWM to
>      work):
>
>      sawtooth -> triangle -> sine
>                           -> square
>
>   3. Any glitches in the triangle-to-sawtooth conversion will be less
>      noticable because the sawtooth has more harmonic content to mask
>      them, while any glitches in the sawtooth-to-traingle conversion
>      will be more noticible as there is less harmonic content to mask
>      them.
>
> The only advantage I can see to a sawtooth core is in visualizing the
> waveshaping.  That is, your waveshaping transfer function looks like
> your output waveform.
>
> Of course a trapezoid core VCO is better still.  :-)
>
>   -- Don
>
> --
> Don Tillman
> Palo Alto, California
> don at till.com
> http://www.till.com