[sdiy] PAIA VCO, LM13700 diode temp comp.

[Ian Fritz]

At 11:51 PM 10/18/05, phillip m gallo wrote:

>I built a pair of VCO's based upon the PAIA scheme for the sawtooth core
>(but used different wave shapers).  As Jim points out the Gm of the OTA is
>what temp. compensates the core.  My variance from the PAIA implementation
>was;
>
>1)using a REF-02 for expo, comparator and waveshaper references.
>2)used MAT-03's for the expo pair,
>3)used an AD823 for the integrator buffer on one VCO and a LF412 for the
>alternate.
>4)implemented a POT for the Hi-Fz tracking adjustment.
>5)"leveled" the MAT03's to the height of the socketed '13700 so they could
>share a piece of aluminum as a common radiator.
>6)As is my general practice i used 1% and 2% film resistors (for what that's
>worth).
>
>I was quite pleased and testing exhibited better results than that reported
>by Ian but one set of test i didn't do was swap a variety of '13700's into
>place to note their effect.  Both VCO's did perform similarly.  The VCO's
>and notes from testing are still in storage although i moved nearly a year
>ago (those who've visited my garage understand).  I'll be digging the VCO's
>out of storage for project reasons in a few weeks and re-run the tests if
>you're interested.

Phillip --

Thanks for the note.  I would be very interested in seeing your test 
results, especially any info on tracking.

My version of this converter uses an LM13600, a 2sa798 transistor pair, and 
a trimmer for the HF tracking.  I changed the input summer from the PAIA 
design to get a different span.  The only other significant change was to 
add a series resistor in the Iabc line -- this helped the tracking a bit 
(something to do with the Early effect).

My guess right now is that the 13600 I have in there is not performing well 
enough.  I have recently bought a number of 13700's and characterized their 
offset change with Iabc and the Iabc linearity.  I'll try one of those 
later today and see if I get better results.

It was good to hear that some one has gotten good results with this 
design.  I'm inspired to have another wack at it.  :-)

   Ian