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'[EE] : amplifier using hex inverter ??'
2001\01\05@064001 by ckchan

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Greetings,

have anybody heard anything about amplifier circuit using hex inverter
chip and other discrete ? where can i find more info ? thanks in advance
!


regards,
ckchan

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2001\01\05@072902 by Jinx

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> have anybody heard anything about amplifier circuit using hex
> inverter chip and other discrete ? where can i find more info ?
> thanks in advance

You need to use a feedback resistor (from output to input) of a
meg or two, to get the inverter into its linear region. They can be
quite sensitive and a bit "twitchy"

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2001\01\05@073738 by Michael Rigby-Jones

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> -----Original Message-----
> From: Jinx [SMTP:joecolquittspamKILLspamCLEAR.NET.NZ]
> Sent: Friday, January 05, 2001 12:32 PM
> To:   .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
> Subject:      Re: [EE] : amplifier using hex inverter ??
>
> > have anybody heard anything about amplifier circuit using hex
> > inverter chip and other discrete ? where can i find more info ?
> > thanks in advance
>
> You need to use a feedback resistor (from output to input) of a
> meg or two, to get the inverter into its linear region. They can be
> quite sensitive and a bit "twitchy"
>
Performance is definately not in the upper class of amplifier design, and my
experience with these designs has been the same as Jinx's.  Sometimes they
work fine, sometimes not.  ISTR you had to use the unbuffered gates if you
are using the 4000 series.  The buffered ones never worked well.  With LM324
type op-amps costing pennies, I don't really see the need to use logic gates
other than out of curiosity.

Mike

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2001\01\05@074744 by Jinx

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> > have anybody heard anything about amplifier circuit using hex
> > inverter chip and other discrete ? where can i find more info ?
> > thanks in advance
>
> You need to use a feedback resistor (from output to input) of a
> meg or two, to get the inverter into its linear region. They can be
> quite sensitive and a bit "twitchy"

That's for CMOS. TTL will (I think) be in the mid-hundreds of ohms.
I should qualify the "twitchy". With the limited experience I've had
with inverters as amps, I didn't expect op-amp flexibilty. However,
the use I had was quite a simple, narrow one for a specific signal
and it was quite easy to fall outside of the linear range and lose
output or severe clip it

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2001\01\05@075817 by Jinx

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> Sometimes they work fine, sometimes not

Something else to consider is repeatability. Chips with the same
part number but from different manufacturers do not always work
the same. For example a Texas 4069 may not work in a circuit
although a Philips 4069 might. Just a guess, but linear applications
may show up differences even more

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2001\01\05@082109 by Alan B. Pearce

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Using digital chips as linear devices is best left to using them as oscillators
in microprocessors. You will find that almost every micro has a single gate set
up for exactly this use. trying to use them as general purpose linear devices is
almost bound to produce tears of frustration as there is no temperature
stabilization in the linear region, and no characterization of gain. It may even
be that various characteristics of the active devices are chosen limit the
ability to operate in the linear region, except where the gate is being built in
as an oscillator.

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2001\01\05@102916 by Olin Lathrop

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> > have anybody heard anything about amplifier circuit using hex
> > inverter chip and other discrete ? where can i find more info ?
> > thanks in advance
>
> You need to use a feedback resistor (from output to input) of a
> meg or two, to get the inverter into its linear region. They can be
> quite sensitive and a bit "twitchy"

It also has to be a CMOS inverter, which is really an amplifier with a gain
somewhat less then -1.  TTL and other logic families won't work.  And of
course don't use a schmidt trigger.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, RemoveMEolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2001\01\05@104735 by Alan B. Pearce

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>It also has to be a CMOS inverter, which is really an amplifier with a gain
>somewhat less then -1.  TTL and other logic families won't work.  And of
>course don't use a schmidt trigger.

People did use to use TTL inverters for oscillators, but they do require lower
value resistors than CMOS. I do remember seeing an article in an English
magazine called Wireless World (this would have been in the 1970's) by someone
who made a multi input audio mixer from a multiple input TTL gate. It is
do-able, but not worth the effort. I agree a schmitt trigger gate will not work.

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2001\01\05@105415 by Maurizio Viterbini

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Hi Ckchan,
The Application Note AN-88 from National Semiconductor (Logic Databook 1984)
explain how to use CMOS inverters in the linear region. High gains only can
be obtained but CMOS inverters can be usefull as post amplifier.
Ciao, Maurizio
ckchan wrote:

{Quote hidden}

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2001\01\05@111252 by Spehro Pefhany

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At 10:18 AM 1/5/01 -0500, you wrote:

>It also has to be a CMOS inverter, which is really an amplifier with a gain
>somewhat less then -1.  TTL and other logic families won't work.  And of
>course don't use a schmidt trigger.

It has to be an *unbuffered* (UB) CMOS inverter to get good results, though as
some have said you can sometimes use LSTTL inverters etc. for oscillators.

The problem with using a buffered version is that there are internal nodes
that you cannot get at in order to compensate the amplifier to get some
phase margin. It can thus oscillate internally (which is a BAD thing).

Actually the gain near the transition (where you bias it) is much more
than 1, you can reduce it to some controlled value by using a couple
of resistors.
                      R2
               x----/\/\/\/\---x
  C1     R1    |               |
0--||--/\/\/\---x-----|>o-------x----> out


Gain ~= -R2/R2 , for reasonably low values of R2/R1
Input impedance ~= R1 for Xc << R1
Vout (dc) ~= Vdd/2 (but quite variable, see the data sheets)

I'd suggest only doing this with 40xx series CMOS, the Iq of the
parts such as 74HC and so on may be quite high.

Best regards,

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2001\01\05@115833 by Don Hyde

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We (and our customers) have built several million radios using a section of
74AC02 or 74LVC02 gate as an rf amplifier in a tripler going from around 100
MHz to 300 MHz.

It works great and is incredibly compact and cheap for the application, but
it's definitely not for the faint of heart.

It took extensive Monte Carlo simulations plus a lot of bench time to get it
right so that production yields were acceptable, and every time the
manufacturer does a die shrink or makes any process change, it all has to be
done again.  For different manufacturers, it usually requires a change in
some of the biasing resistors, so a second source is possible, but requires
a separate bill of materials to cover the changes to other components, not
to mention all the extra testing to assure that FCC compliance hasn't been
compromised.

I would say that it would take many many thousands of units for the few
cents savings per unit to recover the added engineering costs over using a
chip that was designed to be an amplifier.

> {Original Message removed}

2001\01\05@125745 by Dan Michaels

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At 07:30 PM 1/5/01 +0800, you wrote:
>Greetings,
>
>have anybody heard anything about amplifier circuit using hex inverter
>chip and other discrete ? where can i find more info ? thanks in advance


As already mentioned, trying to use a digital gate as an analog
device by hooking up in a basic opamp feedback arrangement probably
doesn't give very good results. If all you are after is rail-to-rail
outputs, then better to just go with a CMOS opamp - LMC660 or
LMC6032 are cheap enough.

Alternatively, I have seen ckts [don't remember where] where
CMOS gates are placed "inside" the feedback loop at the output
node of a regular opamp. The gates can be either inverter or
noninverter - just change the +/- pin connections at the opamp
to compensate.

              _ bipolar
             | \opamp
       o-----|+ \
             |   >----CMOS---+---->
           +-|- /     gate   |
           | |_/             |
           |                 |
           +---------R2------+
           |
           R1
           |
          gnd

Why might you want to do this? To get rail-to-rail at output.
Also, you can simply parallel the 6 gates in the CMOS chip and
increase the output drive - probably to the 50-100 mA range. I
am not sure what the slew rate of this arrangement would be
however - but using newer 74ACxx chips might make it pretty fast.

There is some question - raised by piclisters in the past - about
current draw throught CMOS chips when running in the linear region,
but personally I don't think this is really a problem. They are
made to run at high speeds and drive capacitive loads, where both
channels are mostly open anyways. [also, prototyping & smoke-testing
are half the fun].

hope this helps,
- Dan Michaels
Oricom Technologies
http://www.oricomtech.com
=========================

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2001\01\06@102859 by uter van ooijen & floortje hanneman

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you mean
- inverter gate put in linear mode by feedback resistor -> check "cmos
cookbook" by Don Lancaster
- PWM audio amplifier -> at least 2 versions in elektuur, but I don't known
from when
Wouter

{Original Message removed}

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