Temp. compensated VCO

[Henri Kovalainen]

 The message was originally private, but I guess this is well suited to be
 on the list too.

On Wed, 19 Aug 1998 jorgen.bergfors at idg.se wrote:
> Hi Henri. I suppose this VCO is based on the temperature compensation circuit 
> on Rene Schmitz' web page. I'm thinking of building it too. Have you used his 
> circuit exactly or do you have a schematic on your web site? If you used his 
> circuit, which one - the one with a 4093 or the one with a 555?

 I suggest that you take a look at the actual board. The design is exactly
 the same, but I have added a simple inverting mode sumup op-amp to sum
 the pulsewidth modulation voltages. Rene said that there were some
 problems with the 4093, so the board is for the 555 version, as the 8 pin
 ic indicates.

> Have you done any tests to veryfy that the temperature compensation indeed 
> works?

 I have put all my oscillators through the same kind of torture. I used a
 small nut and a soldering iron to heat the array slightly (I guess the
 temp was about 80C at the max) and there was no actual noticeable drift
 in the frequency. I'm planning of setting up a proper heater and a
 frequency counter and plot a curve of the frequency over the whole
 realistic temperature range.

> If the amplitude of the saw wave varies, it will be difficult to convert
> it to triangle and sine waveforms. Do you think this can be fixed?

 The amplitude doesn't vary "on the fly". I meant that different component
 selections around the CCO may change the amplitude, but this will of 
 course result in a constant value. The final amplitude is determined with
 the feedback resistor. On the other hand, the saw amplitude makes a big 
 difference in the comparator which is used to generate the squarewave, so
 you could even use a trimmer if you wish

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