SEM VCO buffer (schmitt triggers)

[Rene Schmitz]

At 03:35 10.08.99 -0400, you wrote:
>OK so I was wrong about temperature performance of CMOS schmitt, its really
>quite good over a very wide range. Not guaranteed at any one value, but very
>stable at wherever it is.

But you are right about the thresholds, these vary much from 
manufacturer to manufacturer.

I had used the 4093 in my first VCO, in '96 when I was a newbie at 
synthesizer circuitry and this list. And I had to readjust the levelshift
when swapping the 4093s worse still the amplitude varies. (I went over to
the 555 and later the 7555 as schmitt triggers for VCOs.)

One comment on schmitt triggers in the discharge section of a VCO: 
In theory you get smaller discharge times, because when the trippoints are
(for example) 5V and 10V, one has a discharge time of 0.69RC, (R being the
discharge switches resistance. Instead when discharging fully, you have the
5*RC rule of thumb. 
This all is of course only true when the switch behaves really resistively
over 
the whole discharge swing. (Diodes for example.) 
FETs or MOSFETs behave rather as a current sources here. (always some
voltage across them)
Rds(on) isn't important but rather Idss.

Bye
 René


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