[sdiy] VCO reset time

[Scott Gravenhorst]

harrybissell <harrybissell at prodigy.net> wrote:
>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 ???

Uh boy, I guess we need matched capacitors ???  I know nothing of
trapezoid VCO topology, 2 integrating capacitors?  I'd be interested in
looking at a schematic.


>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
>

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