Author Topic: CMOS Inverters with Fewer Gates?  (Read 2425 times)

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jafo

CMOS Inverters with Fewer Gates?
« on: May 12, 2012, 11:56:45 AM »
Are there any such chips available? Hex inverters have too many gates for my needs -- two or three would be ideal -- and it seems wasteful to just tie the extras to ground.
I know that mojo in electronics comes from design, but JFETs make me wonder...

Earthscum

Re: CMOS Inverters with Fewer Gates?
« Reply #1 on: May 12, 2012, 12:44:59 PM »
Give a man Fuzz, and he'll jam for a day... teach a man how to make a Fuzz and he'll never jam again!

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Mac Walker

Re: CMOS Inverters with Fewer Gates?
« Reply #2 on: May 12, 2012, 01:20:54 PM »
I've wondered if a PMOS and NMOS transistor with the gates tied together would acheive the same function (this is all a CMOS inverter is).

Smaller than any 4XXX series chip as well (if you were only interested in one or two).



Earthscum

Re: CMOS Inverters with Fewer Gates?
« Reply #3 on: May 12, 2012, 03:01:47 PM »
After digging through Mouser, it looks like you're better off tying gates to the voltage rails. Everything is SMD or cost way more than a CD4049.

Don't let the "waste" bug ya too much... I assume you haven't looked into an Orange Squeezer yet, lol. That one pains me because you waste half an entire Op Amp. There is a mod to use the other half for full wave recti, but the stock unit...  :icon_frown:
Give a man Fuzz, and he'll jam for a day... teach a man how to make a Fuzz and he'll never jam again!

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R.G.

Re: CMOS Inverters with Fewer Gates?
« Reply #4 on: May 13, 2012, 10:36:55 AM »
Fairchild makes the "TinyLogic" series, which are single and double gates, flipflops, etc., intended for sprinkling around the PCB instead of running traces to packages.

The gotcha is that they are only SMD, and only one of the lower-voltage CMOS families. They can only go to about 5-7Vdc maximum on the power supply to the chip, not the 3-18V of primordial CMOS.

A complementary N-P pair of MOS transistors is in fact the simplest "NOT" gate, but the gain is usually low and the gate capacitance high, meaning that it doesn't do all that good a job as an inverter. It's an OK amplifier, if what you want is the CMOS-as-linear-amplifier uses, but since these are relatively huge CMOS devices, it will conduct a huge current, so you have to worry about how to run the supply voltage down so you don't kill the power supply in linear mode.
R.G.

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puretube

Re: Discrete TubeLess...
« Reply #5 on: May 14, 2012, 04:04:17 PM »
I've wondered if a PMOS and NMOS transistor with the gates tied together would acheive the same function (this is all a CMOS inverter is).

Smaller than any 4XXX series chip as well (if you were only interested in one or two).

old thread is long...

liquids

Re: CMOS Inverters with Fewer Gates?
« Reply #6 on: May 14, 2012, 07:53:30 PM »
I understand the obsession with efficiency or the lack therof, trust me.

While I try to find work arounds for circuits that want just one 40106 stage.....using just 1 stage of a 6 stage chip is as likely as using all 6, if you think about it from a design standpoint.  likewise, God forbid you end up needing another stage if used all 6 in a 40106!  Then you need a second chip where 5 stages are unsused...etc.

Again, while I personally try to find work arounds for circuits that want just three channels of a quad op amp package...or just one channel of a dual op amp package..And a single channel op amp has as many pins as a dual.  A quad op amp with an unused channel has half the power pin connections and 2 less overall pins as two dual op amps or a dual and a single channel op amp.

14 pin chips are just a package...made by manufacturers, not FOR builders.  Keep that in mind.

I'd imagine that's why they don;t have 12 pin, tri-op amp chips...etc.  

If you're only using 1/2 the stages in a CMOS chip, use the others to re-inforce each of the ones you are using or tie them to ground.  Look at this way - if you tie the unused to ground, you have a lot of options for layouts - whatever pins are most convenient for you to use can be utilized, while the others connect to ground.

It's not a waste, or it can be worked around in most scenerios.  And really...there's no shame in tying them to ground in the logic realm.  Op amps can do so many thing...logic stages just don't have that kind of 'swiss army knife' appeal - they do what they do, they're in there to do that, and trying to come up with ways to use the stages you're not using is more trouble than it's worth.  It's not bad design not to use every logic stage of a CMOS chip.
« Last Edit: May 14, 2012, 08:00:27 PM by liquids »
Breadboard it!

earthtonesaudio

Re: CMOS Inverters with Fewer Gates?
« Reply #7 on: May 15, 2012, 08:16:06 AM »
There are no extra inverters, only unrealized functions.

Earthscum

Re: CMOS Inverters with Fewer Gates?
« Reply #8 on: May 15, 2012, 11:01:56 AM »
There are no extra inverters, only unrealized functions.

Aye... a really simple one is extra current into a tone stack by piggybacking one of the unused stages. This, from the little bit I've played with it, gives some excellent results. I was gonna try this with a state variable filter and mix the LP and BP (Thanks, Ronan!). I just haven't decided how I want to implement the variability, lol... different topic altogether for that, though. Basically, I can use the entire package as a sort of "inline package" if it works. Way too convenient NOT to try it.  ;D
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liquids

Re: CMOS Inverters with Fewer Gates?
« Reply #9 on: May 15, 2012, 08:02:32 PM »
Define piggybacking....two inverters in parallel?
Breadboard it!

thehallofshields

Re: CMOS Inverters with Fewer Gates?
« Reply #10 on: September 11, 2017, 05:36:56 PM »
Define piggybacking....two inverters in parallel?

Piggybacking on this thread...

Do you guys think it would be possible to use the Inverters for bypass switching? I swear I've seen this done before.

amz-fx

Re: CMOS Inverters with Fewer Gates?
« Reply #11 on: September 12, 2017, 03:52:57 AM »
I have seen use of the 4007 for bypassing in some older pedals made by Pearl (if I am remembering that correctly). Because of the limited number of transistors to work with, it is mainly for buffered bypass.

Best regards, Jack

marcelomd

Re: CMOS Inverters with Fewer Gates?
« Reply #12 on: September 13, 2017, 07:42:36 AM »
DOD used 4007s for bypass. Usually as two inverters and a single nmos connected as a flip flop, driving two jfets for the signal.

I built a pedal using a 4007 as three inverters. Two latching a relay plus one as an overdriven amp. Takes a lot more space than a 4069, but I liked the challenge =)

amz-fx

Re: CMOS Inverters with Fewer Gates?
« Reply #13 on: September 13, 2017, 07:48:41 AM »
I have seen use of the 4007 for bypassing in some older pedals made by Pearl (if I am remembering that correctly). Because of the limited number of transistors to work with, it is mainly for buffered bypass.

I looked at the Pearl OD-5 schematic and it is a good example. Two of the inverters make the alternating flip-flop, and the remaining two mosfets are used individually as audio switches. No relays or external jfets are used with it.

regards, Jack