[sdiy] unbuffered CMOS

[Scott Gravenhorst]

"anthony" <aankrom at bluemarble.net> wrote:
>
>> 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
>
>Yes exactly.
>
>> 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
>
>I remember reading at least in some applications they're biased like a Class 
>A amp.
>
>> 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
>
>Tube-like. That's good to know. But is the reason for using an unbuffered 
>inverter because of the increased current usage or that it sounds better?

Well, it's not a tube, but produces tube like results in some cases.  Better?
 I dunno.  Certainly not as bulky or heavy as tube equipment would be.
 
>I've seen similar applications that don't specify unbuffered.
>
>(I put unbuffered CMOS as the subject, and inverters were the only thing I'd 
>seen used in this manner, but I wasn't sure if it would be doable with other 
>types of gates and uses or not...)

I'm not sure if I've seen anything other than unbuffered inverters.  3 types I
know of, 4007 is a transistor array of symmetrical P and N MOSFETs, 4069UB is
a hex inverter, again with symmetrical transistor pairs, and 4049 UB with
assymmetrical transistor pairs, capable of sinking more current than of
sourcing it.

>> distortion boxes using the technique.  The René Schmitz 4069UB VCO employs 
>> it.
>> I have an ADSR that uses it.
>
>I just started building that VCO last night. Pretty cool.
>
>That's the main one that got me thinking about this.
>
>Also Osamu Hoshoyama's excellent web page.

Yes, he does.  Very interesting work with MOSFETs, an experimental filter
using an OTA built from CMOS.  Not for the faint of heart as I read 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.
>
>That's what I thought.
>>
>>>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...
>
>Yeah I like it just about as much as the 4046. 

Note that you can make a VCO (without the PWM part) or an LFO using a 4007. 
Lots of cool stuff.

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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