AW: Re: Compensated Exp generators and V

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Thu Jun 8 21:55:00 CEST 1995


> Then you can use a vfet or bipolar transistor to discharge
> the cap real fast so you don't need the discharge compensation (which
> screws with the amplitude and gives the sine waves a bit of an edge).

Good point. I never thought about the effects of the slightly distorted
saw on the sine; there it is crucial inddeed!


> I'd also recommend using a transistor array where you can heat the
> substrate directly with very little current (instead of aiming a
> blowtorch at the LM394).
>
> It seems that a more accurate comparator can be built by wire-or-ing
> two comparators together; one detects the positive trip point, one the
> negative.  You see this configuration in lots of application notes.

I built a VCO with a heated 3086 plus dual comparator and flipflop some
years ago. There were other problems (which I spoke about some times ago),
but the overall funtion is very fine.
I thought to go one step further, replacing the flipflop. I planned to use a 
discrete
flipflop with 4 transistors (originally I used 2/4 CD4011), and 2 of those 
transistors
would be the internal comparator outputs (I used 2/4 LM339 which has open 
collector
outputs).
I have abandoned this project for 3340 VCOs, however. Perhaps some time I 
will
try it again!

JH.



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