[sdiy] very simple vco

[Scott Gravenhorst]

=?ISO-8859-1?Q?Ren=E9_Schmitz?= <uzs159 at uni-bonn.de> wrote:
>
>Hi Scott and Mike,
>
>>>>But as pointed out in another posting...it is the expo converter that
>>>>makes the VCO's complicated.
>
>No, merely makes understanding its function more difficult. The work for 
>soldering it together is about the same.

Yeah, as I considered this VCO, I mentally noted that the expo circuit you used
is quite a bit simpler than a linear V-I converter.

>This seems to be based on the thinking that once you eliminate the expo 
>converter the temperature problems would be gone. This isn't necessarily 
>true! Linear current sources can have similar problems, and the CCO 
>cores can exhibit drift on their own. Oscillator design is always a 
>delicate matter.

Ok, 2 parts I don't understand here: temperature problems with this particular
CCO and temperature problems with a linear current source.  

It was my understanding that the linear current source is accurate because the
summing node causes copying of the input current by ensuring the node remains at
zero volts through the opamp output doing whatever is necessary to make that
happen.  I can't see how temperature effects or even nonlinearities in the
feedback loop would upset this.  Obviously I am missing something.  Whatever
temperature effects there are, I would guess they are minor since my linear VCOs
seem to stay in tune.

>>>Keep in mind, Luca asked about "a simple, almost primordial VCO", not a
>>>"musically useful" VCO (or what the more advanced members of this community
>>>would consider "useful").
>
>I think 9+ octaves qualifies as being "musically useful". :-P
>
>Ok, its not the most stable VCO with regard to drift. But not really bad 
>either.

As for this particular 4069 CCO, what is it about it that makes it "unstable"? 
What causes the drift?  Is this a CMOS temperature thing?  As you say, it
doesn't seem all that bad.


>[snip]

>Cheers,
>  René
>
>-- 
>uzs159 at uni-bonn.de
>http://www.uni-bonn.de/~uzs159
>
>
>

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