[sdiy] Newbie question regarding the 4069 VCO

[Roy J. Tellason]

On Wednesday 10 November 2004 09:09 am, James Howe wrote:
> Thanks for the explanation.  This information, combined with the
> information I received from others (Rene, Harry) has been very helpful.
> Your explanation on why the inverter is basically an amplifier was most
> helpful.  I work with software so I tend to think in a more 'digital'
> sense and so I wasn't thinking about the process by which a 'low' voltage
> would become a 'high' voltage.  Your explanation gave me the whack in the
> head that made me understand that in order for a voltage to go from low to
> high it would have to be amplified! (duh)  The one thing that I'm still a
> little unclear on is why in the 4069 case I should be thinking in terms of
> Vcc/2.  I read a Fairchild application note on using an inverter as a
> linear amplifier last night and it said the same thing.  What I don't
> understand is why it's Vcc/2?

It's because when you provide a resistive path from the output of an inverter 
back to its input it "self-biases" to that point...

If you want to play with this sort of part,  I would strongly recommend that 
you get yourself a copy of Don Lancaster's CMOS Cookbook.  I believe that 
they're still available from his web site at tinaja.com.