Post by thread:[EE] Push-pull vs totem pole

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

On Sun, 10 May 2009 15:42:19 -0700 "Vitaliy" <spam_OUTspamTakeThisOuTmaksimov.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

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. ******************************************************************** Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products (978) 742-9014. Gold level PIC consultants since 2000.

>> "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

On Mon, 11 May 2009 12:24:23 +1200 Jinx <.....joecolquittKILLspam@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=Pushâ€“pull_output&action=history John

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

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

>> 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

> 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

>"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 ...

:: 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 -- cdb, colinKILLspambtech-online.co.uk on 11/05/2009 Web presence: http://www.btech-online.co.uk Hosted by: http://www.1and1.co.uk/?k_id=7988359

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

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

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 <johnspam_OUTjcoppens.com> wrote: {Quote hidden}> On Sun, 10 May 2009 15:42:19 -0700 > "Vitaliy" <@spam@spamKILLspammaksimov.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 > -

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 -- FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available!

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

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 <KILLspamwestfwKILLspammac.com> wrote: {Quote hidden}> > 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 > >