ca3080ota.lfo

[Martin Czech]

Has anybody made experiences with the ca3080 OTA/CA3140 buffer 
Function Generator Circuit ?
(as proposed in data-sheet/app. note ca3080.pdf page 4,
(or in data-sheet/app. note ca3140.pdf page 9)

on the Harris web pages:

"http://www.semi.harris.com/datasheets/lin-tel/ca3080/"
"http://www.semi.harris.com/datasheets/lin-tel/ca3140/"

The Harris people claim a 1E6:1 sweep range  (they call it "super 
sweep generator") and there is reason to believe this,
since an oszilloscope foto (1Hz - 1E6 Hz) is supplied in the data sheet.
Ok, they don't tell us about the linearity over such a wide range.
I guess , it'll be awfull and not useable for precision vcos,
but it might serve as a wide range vclfo if I tune it down with a larger cap.
A linear application could be vco in a pll circuit (tri,sin,squa).

Or one could combine this with an  cheap pnp-exponential generator (CA3096 array)
like in the old Formant ota-filters
to approximate an exponential scaling (the CA3096 has two pnps but
they are NOT matched (layout foto)).

I am currently thinking about how to combine this circuit idea 
with the symmetry modulation idea in my last mail. 
A symmetry modulation independent from frequency requires a very large
sweep range, so this could work (more or less).
The MAX038 can only sweep over a range of 500:1, and the frequency will
certainly suffer at both ends if the symmetry is at it's maximum of 90%/10%.
The MAX038 is also quite expensive here in Germany (38,00 DM).


m.c.