[sdiy] unbuffered CMOS

[Scott Gravenhorst]

"anthony" <aankrom at bluemarble.net> wrote:
>I was thinking about the uses that we have for CMOS logic devices in the 
>synth world - both digital and analog - but especially analog.
>
>Sometimes 'unbuffered' CMOS devices are specifically called for. I assumed 
>this was simply because  when using them as analog devices the buffered 
>units would behave more nonlinear in a possibly nondesirable way. But I keep 
>thinking that there're other reasons to use unbuffered devices: seems like 
>they'd use less current.

I assume that you are referring to using an unbuffered CMOS inverter as a
"linear amplifier" by using input and feedback resistors to control the
amplifier's gain.  Doing this actually consumes more current than operating
the gate as a logic gate.  And if you're trying to simulate an opamp, the same
application will usually consume less power if an opamp is used.  A gate used
in this manner will have a  current draw at maximum when both output
transistors are presenting the same resistance, i.e., when the output is
(Vdd-Vss)/2.  The actual current depends on supply voltage and a set of V-I
curves are found in the datasheets.  Gates are used like this in things like
the WASP filter.  Their nonlinearities are tube-like.  There are guitar
distortion boxes using the technique.  The René Schmitz 4069UB VCO employs it.
 I have an ADSR that uses it.

>
>And what's up with 4007UB? It wouldn't B what it B if it wasn't UB...

Well, it probably just conforms to a sort of standard, the unbuffered ICs had
UB appended.

>I wish there was a bipolar version of sorts. I have lots of NPN arrays, but 
>PNP's I don't find much. Both in one package might be very useful. 

That's why I like the 4007...

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