AW: Compensated Exp generators and VCO's

Rick Jansen sscprick at
Wed May 31 18:58:32 CEST 1995

In message <2FCD0649 at MSMGATE.M30X.NBG.SCN.DE> you write:
> > The discharge time is kept very short here by using a
> > HC4066 analog switch instead of a discrete (MOS)FET. FETs
> > with a low Rds,on are hard to find, while the switches in
> > the common HC4066 have an Rds,on of only 25 ohm! Normal
> > MOSFETs have a Rds,on of ca 100 ohm. On the downside: a 5V
> > supply is needed now.
> Another hint: If You use a standard CMOS (CD4066) instead of the
> the HCMOS type (74HC4066), 15 Volts should not be a problem!

No, it *must* be a *HC*4066. The normal CMOS versions have a 
higher Rds,on, ca. 100 ohm, as in a normal FET. There is a note 
in a data book on this specific ic, that the analog voltage and
control voltages may be up to 12V, but it isn't specific about
Vcc in this case.

> Another thought: As the CEM3340 are said to be available soon again,
> I doubt the *need* to go discrete. (If You just want to do it for the
> challenge, that's another thing!).

The CEM chips might be available again, but for how long? They
will remain specialty items. Circuits built from discrete parts
that will be available for a long time to come have a bit more 
charm to me.


Rick Jansen
rick at
S&H's a module and s&h's looking good

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