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'[EE] Push-pull vs totem pole'
2009\05\10@184302 by Vitaliy

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Olin Lathrop wrote in "[AD] Save big on an advanced USB-..":
>>> By the way, what is the push-pull IC you are using? I am also
>>> trying to find out similar push-pull output ICs. ...
>>
>> What's push-pull?
>
> Misnamed "totem pole" in this context.  What he is referring to is the
> ability of the IC to actively drive its outputs both high and low.

[snip]

> As for "push pull", this refers to two stages driving in the same
> directional alternately.

"Totem pole" and "push-pull" both mean the same thing.

=====
Wikipedia: Totem pole (disambiguation)
Totem pole output, also known as a push-pull output, a type of electronic
circuit

http://en.wikipedia.org/wiki/Totem_pole_output
=====

Take a look at this circuit:

http://upload.wikimedia.org/wikipedia/en/7/72/Electronic_Amplifier_Push-pull.png

It's easy to see that the push-pull can actively drive the output in both
directions (HIGH and LOW).

Vitaliy

2009\05\10@192844 by John Coppens

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On Sun, 10 May 2009 15:42:19 -0700
"Vitaliy" <spam_OUTspamTakeThisOuTspammaksimov.org> wrote:

> "Totem pole" and "push-pull" both mean the same thing.

Not necessarily. CMOS outputs are generally push-pull. They have a
P-channel FET above and an N-channel fet below. Both are in digital model
(on/off). 'Totem-pole' will never apply to a CMOS output.

TTL and such have above and below NPN transistors. The lower is really
working in digital mode. The upper NPN is in linear mode, and mainly
serves as an active resistor. There's almost always a diode between both
transistors, which is part of the totem pole output, to protect the upper
transistor, which doesn't even like to go all the way to VCC.

Wikipedia is wrong there... That happens.

John

2009\05\10@201816 by olin piclist

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Vitaliy wrote:
> Take a look at this circuit:
>
> http://upload.wikimedia.org/wikipedia/en/7/72/Electronic_Amplifier_Push-pull.png
>
> It's easy to see that the push-pull can actively drive the output in
> both directions (HIGH and LOW).

Only if you believe the author's claim that this really should be called
"push pull".  Apparently that term has gotten misused since its original
meaning, and that misuse has stuck in at least a few places.  I guess it's a
handy term that seems to be applicable, especially for those that never
learned its original definition.


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2009\05\10@202507 by Jinx

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>> "Totem pole" and "push-pull" both mean the same thing.
>
> Not necessarily

> Wikipedia is wrong there... That happens.

To be fair, the entry does say what you said, and what I understood to
be the difference -

A special configuration of push-pull, though in fact an exception, are
the outputs of TTL and related families. The upper transistor is functioning
as a active pull-up, in linear mode, while the lower transistor works
digitally.
For this reason they aren't capable of supplying as much current as they
can sink (typically 20 times less). Because of the way these circuits are
drawn schematically, with two transistors stacked vertically, normally with
a protection diode in between, they are called "totem pole" outputs

2009\05\11@002054 by John Coppens

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On Mon, 11 May 2009 12:24:23 +1200
Jinx <.....joecolquittKILLspamspam@spam@clear.net.nz> wrote:

> To be fair, the entry does say what you said, and what I understood to
> be the difference -

Yes... That is the modification I just made to the Wikipedia, ;-) Check
history at:

http://en.wikipedia.org/w/index.php?title=Push–pull_output&action=history

John

2009\05\11@004733 by Vitaliy

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Olin Lathrop wrote:
>> Take a look at this circuit:
>>
>> upload.wikimedia.org/wikipedia/en/7/72/Electronic_Amplifier_Push-pull.png
>>
>> It's easy to see that the push-pull can actively drive the output in
>> both directions (HIGH and LOW).
>
> Only if you believe the author's claim that this really should be called
> "push pull".  Apparently that term has gotten misused since its original
> meaning, and that misuse has stuck in at least a few places.  I guess it's
> a
> handy term that seems to be applicable, especially for those that never
> learned its original definition.

You mean, the original definition from the pre-transistor era? Perhaps your
definition needs to be updated? :) The meaning of words can change over
time.

-->FWIW, in Russian this type of circuit that has pnp/npn or
N-channel/P-channes FETs, is called "pushpul'nyi kaskad" (lit. "push-pull
cascade").

The name in this situation, makes total sense: the output is "pushed" by one
transistor, then it's "pulled" by the other one.

Vitaliy

2009\05\11@011951 by Bob Blick

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Vitaliy wrote:

> "Totem pole" and "push-pull" both mean the same thing.

Personally I think totem pole is one implementation of push-pull, since
push-pull can be done many ways.

Digi-key assigns totem pole and push-pull to Microchip's TC54:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556197&keywords=tc54

Looking at Microchip's datasheet, they specify push-pull and
complementary but do not mention totem pole. To me totem pole suggests
the TTL implementation using NPN transistors, not complementary. But I
am not fixed on that definition, if I saw totem pole in a description I
would want clarification of the topology if it was important to me.

I think a lot of reference information is written by people who do not
have a complete grasp of the difference between a principle and an
implementation of the principle.

Cheerful regards,

Bob

2009\05\11@021246 by Jinx

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>> To be fair, the entry does say what you said, and what I understood
>> to be the difference -
>
> Yes... That is the modification I just made to the Wikipedia, ;-)

That's an awfully convenient explanation ;-)))

So often people complain about all manner of things in life but do
nothing to correct it

Good for you

2009\05\11@021905 by Jinx

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> Personally I think totem pole is one implementation of push-pull,
> since push-pull can be done many ways.

To me, it seems totem pole is more like the open collector (RA4)
on many PICs. The low-side transistor is a digital switch for sinking
current, whereas the user-added pull-up/high-side resistor allows
only limited "pushing" or sourcing of Vcc current through it

2009\05\11@035412 by Alan B. Pearce

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>"Totem pole" and "push-pull" both mean the same thing.

Not historically. I am with Olin on this one, but see below ...

Push-pull output has historically been used for valve and transistor
amplifiers that have an output transformer with centre tapped primary, each
half driven alternatively in a Class B configuration. This was the
configuration of output stage that every 6 transistor pocket radio from the
50s through the 70s used.

Totem pole has historically been the term used for the likes of TTL logic
output stages. These devices never used the term push-pull in their
descriptions from the manufacturer.

Possibly there has been some confusion arise through the use of push-pull
for transformerless transistor output stages in audio amplifiers, which
although of a totem pole style circuit configuration, used the term
push-pull.

So from this one ends up using push-pull for linear use, and totem pole for
digital use ...

2009\05\11@042704 by cdb

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:: Push-pull output has historically been used for valve and
:: transistor
:: amplifiers that have an output transformer with centre tapped
:: primary, each
:: half driven alternatively in a Class B configuration. This was the
:: configuration of output stage that every 6 transistor pocket radio
:: from the 50s through the 70s used.

One term I haven't seen used as an alternative to push pull in this
discussion is a complimentary pair output.

I also tend to think of P&P as that used by an amplifier with using an
audio transformer, and complimentary pair in push pull mode for thhe
transformerless version, so for ac signals.

I think one of my first electronics set of books by the venerable
G.N.Patchett referred to the valve amplifier radio circuit as push
pull and the transistor one as complimentary pair. Must race off and
buy some OC81's and 45's !

Colin
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2009\05\11@081351 by Gerhard Fiedler

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Alan B. Pearce wrote:

>> "Totem pole" and "push-pull" both mean the same thing.
>
> Not historically. I am with Olin on this one, but see below ...
>
> Push-pull output has historically been used for valve and transistor
> amplifiers that have an output transformer with centre tapped
> primary, each half driven alternatively in a Class B configuration.
> [...]
>
> Totem pole has historically been the term used for the likes of TTL
> logic output stages. [...]

So it seems you are saying that neither term is (in its "pure" meaning
:) to be used for a digital output that drives actively high and low
(with about equal drive capability). How would you call such outputs? Is
there a generic term for this capability?

FWIW, it seems that "historically" (for shorter values of "history" :)
I've seen "push-pull" being used a lot for digital outputs that drive
actively high and low (with about equal drive capability). May not be
the first meaning, but seems to be the more common meaning. AC
amplifiers with center-tapped transformers in the output are not that
common anymore.

BTW, I think there are a few terms that changed their meaning over time,
accompanying the changes in technology. I can't think of one right now,
but I'm sure some here can :)

Gerhard

2009\05\11@090507 by Derward Myrick

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----- Original Message -----
From: "Alan B. Pearce" <.....Alan.B.PearceKILLspamspam.....stfc.ac.uk>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu>
Sent: Monday, May 11, 2009 2:54 AM
Subject: Re: [EE] Push-pull vs totem pole


{Quote hidden}

> --

2009\05\12@155549 by Bob Axtell

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I have found Wiki to be wrong MOST of the time on technical matters.

--Bob

On Sun, May 10, 2009 at 4:28 PM, John Coppens <johnspamspam_OUTjcoppens.com> wrote:
{Quote hidden}

> -

2009\05\12@165607 by Harold Hallikainen

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I first heard the term push-pull to refer to vacuum tube audio or RF
amplifiers where the plates were tied to opposite ends of a transformer
primary, and the supply was connected to the center. Each tube alternately
pulls its end of the transformer to ground. Maybe we should have called it
"pull-pull."

I first heard "totem pole" output referred to in TTL. This output uses a
common emitter NPN transistor to pull the output down, and another NPN
operating as an emitter follower to pull the output up. It resembled a
"totem pole" since the two identical transistors were stacked.

Then, moving in to solid state audio amplifiers, we had the "complementary
emitter follower" where an NPN as an emitter follower pulled the output
up, and a PNP, again as an emitter follower, pulled the output down.
Substituting P channel and N channel FETs for the transistors, we got CMOS
outputs.

So... that's how I recall the terminology.

Harold


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2009\05\12@171415 by William \Chops\ Westfield

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On May 12, 2009, at 12:55 PM, Bob Axtell wrote:

> I have found Wiki to be wrong MOST of the time on technical matters.

You mean like SUBSTANTIALLY WRONG to the point of being useless, or  
"wrong in the subtle details of ill-defined technicalities, once you  
talk to experts?"  It's my conviction that one of the best ways to  
learn about something is to have two people who know more about it  
than you do ARGUE about it at a level slightly over your head.

I'm wondering where I can find a better lay explanation of push-pull  
vs totem pole.

And What's an "active pullup" anyway?  Isn't that a bit of a  
oxymoron?  Just because the amount of current available is limited  
doesn't make it not a current source, does it?

I would define "push pull" as any output that can both sink and source  
current, in either analog or digital circuits.  Totem pole outputs in  
TTL, the CMOS output stage of CMOS logic, and your typical speaker  
amplifier are all examples of push-pull outputs.  The usual  
alternative is "open collector" or "open drain" outputs, where there  
is only the choice of sinking current or being "off."

BillW

2009\05\12@184532 by Bob Axtell

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Usually wrong on the REASONS why things are the way they are..

--Bob

On Tue, May 12, 2009 at 2:14 PM, William "Chops" Westfield
<KILLspamwestfwKILLspamspammac.com> wrote:
{Quote hidden}

>

2009\05\12@203237 by Gerhard Fiedler

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William "Chops" Westfield wrote:

> I would define "push pull" as any output that can both sink and source
> current, in either analog or digital circuits.  

Ah, with this, you'd leave the pure world, though, and be just where
things work... at your peril :)

Gerhard

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