[sdiy] VCO reset time

[Don Tillman]

   > 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