doubts on transistor configuration??

[LvW]

I must confess that I am able to observe a phase difference between a sinusoidal input voltage at the base and the amplified signal at the collector terminal of a common emitter configuration.

 

[Syncopator]

I am able to observe a phase difference ... et etc

No you can't.

What you observe is an inverted copy of the input. You call it phase difference because many other people do too, and you are simply copying them.

I've seen it so often in other areas of electronics and in misuse of the English languuage. A poorly prepared teacher or author will pass on their own errors and misconceptions - because "everybody else" does it.

And so the myths live on.

Maybe I'll put a couple of diagrams together to deal visually with this particular matter.


addendum: I remember reading, some decades ago, in one of the pretigious monthly electronics magazines, a brief discourse on the same subject.
Mention was made of a failed design of, if I remember correctly, some measuring equipment. The design failed because the incorrect assumption had been made that the signal at the collector of a CE stage was 180° different in phase from that at its base.

 

[LvW]

Maybe I'll put a couple of diagrams together to deal visually with this particular matter.

Yes, that's agood idea.
Nevertheless, when I compare two different sinusoidal signals of the same frequency (even without knowing the sources of information) I have no problems to define a phase shift between both - even in case of 180 deg. Why do you think I can't?

It's even worse: In the past, I was able to measure a phase difference between two signals (as described above in posting #21).

 

[FvM]

I fear, you have come to a deadlock in this discussion. Just consider a blackbox (e.g. an arbitrary function generator) with two signal outputs. You observe two signals of same frequency and shape, e.g. sines. You are pretty able to measure a phase difference between them, a good job for a beginners lab. You can do that without knowing how these signals are generated, may be one is just "an inverted copy". Phase difference is simply an objective property that can be measured. Contradicting the phase difference, if the signal had been inverted sounds absurd in my ears.

I would also raise an objection, if you call the signal phase shifted, although you know, it's out-of-phase due to simple inversion. Thus I tried to distinguish between both formulations in post #19. Phase shift is in my opinion more related to the process of generating a phase difference. Others may have less problems to call the signal phase-shifted as well.

 

[betwixt]

I think the point Syncopator is making is that there is no time difference between the signals, one is an upside down but immediate copy of the other. We normally measure phase difference as being the delay between the same points on two versions of the same waveform and quantify it as a proportion of time shift relative to a whole cycle. It's an acedemic point, I think we all refer to inversion as 180 degrees out of phase even when there isn't a half cycle delay. It's one of those cases where language and technology have drifted apart but common understanding has kept us all thinking along the same lines.

Brian.

 

[LvW]

I think the point Syncopator is making is that there is no time difference between the signals, one is an upside down but immediate copy of the other. We normally measure phase difference as being the delay between the same points on two versions of the same waveform and quantify it as a proportion of time shift relative to a whole cycle. It's an acedemic point, I think we all refer to inversion as 180 degrees out of phase even when there isn't a half cycle delay. It's one of those cases where language and technology have drifted apart but common understanding has kept us all thinking along the same lines.
Brian.

I could imagine that Syncopator was referring to time delay. But in this case, I think, he restricts himself (and his definition) on two signals (a) coming from the same source and (b) carrying a sort of information that allows to detect a time shift (delay). But I think, the usage of the term "phase" is more general.
What about the phase-locked loop? Two signals from two different sources are compared and the phase difference is used as control signal.
Is this a misuse of the term "phase difference" (because there are no information points to detect a time difference)?

 

[Syncopator]

In this picture I have identified the same peak after phase shifts of 45, 90, 135 and 180° and after inversion.

 

[betwixt]

I think we all understand that Syncopator. The discussion is whether the top and bottom signals in your picture are actually phase shifted or inverted. As you illustrate clearly, there is a measurable time delay between the peaks as the phase differences are applied to the waveform. The debate is over the difference between inversion and 180 degrees shift. Certainly, a repetitive signal delayed by one half cycle looks upside down compared to its start point but it is the delaying process that causes that. In an inverter the signal is instantaneously mirrored in the X axis so there is no delay involved. So is it still shifted 180 degrees?

It's an interesting topic and I'm sure we all know what the electrical results are but the technical definition could keep us chatting for hours.

Brian.

 

[LvW]

Hi Syncopator,
your picture is not really surprising - as mentioned already, we could imagine what you was referring to.
Of course, you are free to use your own definition for "phase difference" or "phase shift" - and in the particular case under discussion I agree with you that the term "inversion" indeed is a bit more correct than "phase shift".
However, this is possible only because you know the circuitry (and the operation involved) which are both signals coming from.
Without this knowledge - and for a continuous symmetrical signal like a sinusoid without such a marked point as in your picture - we are not able to decide between "inverted" or "shifted". Therefore, I repeat: I will be able (and I was able in the past) to detect a phase shift between the input and output signal of a BJT amplifier.
I think, that is the reason we are using the term "phase shift" for all cases in which two signals of the same frequency are compared to each other.

Finally, I am not quite sure if it is really an important and "an interesting topic" (as Brian thinks). In fact, it is a discussion on definitions only, is it not?

Regards
LvW

---------- Post added at 11:33 ---------- Previous post was at 11:17 ----------

Syncopator, one question (theoretical): In a textbook on mathematics there is a sentence "multiplying a sinusoid with -1 is identical to shift the phase by 180 deg.".
Right or wrong?

 

[Syncopator]

The discussion is whether the top and bottom signals in your picture are actually phase shifted or inverted.

Discussion? There is no discussion Brian, the top and bottom signals are inverted. Nothing more, nothing less.

In an inverter the signal is instantaneously mirrored in the X axis so there is no delay involved. So is it still shifted 180 degrees?

Most certainly not.

Of course, you are free to use your own definition for "phase difference" or "phase shift" ...

That's very magnanimous of you, but it isn't my definition. The fact it is, whether you like it or not and whether you accept it or not, that inversion is not the same thing as a phase shift, of 180° or any other angle.

- and in the particular case under discussion I agree with you that the term "inversion" indeed is a bit more correct than "phase shift".

Your magnanimity knows no bounds. However, in the case under discussion "inversion" is the only applicable term.

Finally, I am not quite sure if it is really an important and "an interesting topic" (as Brian thinks).

Yes, it is very imnportant. I have already mentioned in my post #22 that people have been caught out because they thought, incorrectly, that there was a phase shift between the emitter and collector of a CE stage. It must have been a hard lesson for them and I bet they probably argued with their colleagues beforehand .....

In fact, it is a discussion on definitions only, is it not?

I really don't think you need an answer to that.

Syncopator, one question (theoretical): In a textbook on mathematics there is a sentence "multiplying a sinusoid with -1 is identical to shift the phase by 180 deg." Right or wrong?

It is quite wrong. Unfortunately, textbooks do carry errors. Many of them are because, through no fault of the author's, they are labouring under a misconception. As I mentioined post #22 of this thread, if someone is taught incorrectlly, or, failing tuition, they pick up wrong information in forums or an other technical sites, they don't know any better, and the longer they harbour misconceptions the harder it is to correct them. Some of the never do.

Look for instance at the confusion which reigns in the abbreviation of units and indeed in the units complete names, and abbreviations in general - I'm talking about when to use upper or lower case letters.

The former used to be taught once in a while in the technical press but I haven't seen such articles for decades. As far as abbreviations in general is concerned we used to be taught the rules in English classes at school.

When it comes to doing most things, you will usually find that there is more than one way, sometimes many ways, of doing them. And, usually, there is only one correct way.
It boils down to being taught properly. Not just doing things "like this" because "everyone else" does it so.

As I say, old habits die hard - if, indeed, they ever do.

With my regards to you both.

 

[FvM]

The fact it is, whether you like it or not and whether you accept it or not, that inversion is not the same thing as a phase shift, of 180° or any other angle.

I didn't hear anyone say they are "the same thing".

But anyway, I want at least to add my own visualization of the "phase shifted by 180°" or "Inverted" case. The below waveform continues my post #24. The problem is, that my oscilloscope doesn't display those enligthening red circles. And I unfortunally forgot to notice the measurement setup (I know, this shouldn't happen). But you surely can tell, if the 180° phase difference was generated by signal inversion or phase shift?

 

[DartPlayer170]

It is quite wrong. Unfortunately, textbooks do carry errors. Many of them are because, through no fault of the author's, they are labouring under a misconception.

I'm sorry, but in Mathematics: -Sin(theta) = Sin(theta+Pi)
It is most certainly not a mistake
Mathematically, the left side is equivalent to the right side for every instance of theta.

The only reason why there is any issue in electronics is because it is possible that the signal is not sinusoidal or a Fourier transform of Sines.
However, there are very few, if any, real applications for signals that are not a combination of DC offset and Fourier Transforms.
In oscillator circuits, it is a vital part of the theory that the output is phase shifted. Try to explain an oscillator circuit from a CE configuration because of inversion!

 

[Syncopator]

The below waveform continues my post #24. The problem is, that my oscilloscope doesn't display those enligthening red circles. But you surely can tell, if the 180° phase difference was generated by signal inversion or phase shift?

By looking only at the 'scope display, and not knowing where the two traces came from (unlikely), it is impossible to say.

But looking only at the CE circuit, one knows from the circuit's operation that there is an inversion. No instrumentation is necessary.

 

[nitin.maurya1]

i think we are diverting from the basic question which is asked by thread author, i also have same problems in deciding configuration of transistors in circuit.
please give your valuable views for deciding configurations of trasistors in circuits (digital or analog)

 

[FvM]

i also have same problems in deciding configuration of transistors in circuit.
please give your valuable views for deciding configurations of trasistors in circuits (digital or analog)

What's your point in deciding about configurations? If a circuit doesn't clearly implement a particular prototype, as e.g. the discussed transistor stage with two ouputs, there's nothing to decide.

 

[LvW]

It is quite wrong. Unfortunately, textbooks do carry errors. Many of them are because, through no fault of the author's, they are labouring under a misconception. As I mentioined post #22 of this thread, if someone is taught incorrectlly, or, failing tuition, they pick up wrong information in forums or an other technical sites, they don't know any better, and the longer they harbour misconceptions the harder it is to correct them. Some of the never do.

Here are some frequently used identities, which I still consider as correct:

sin(beta+180deg)=-sin(beta)

exp(j*Pi)=-1

(1/jwt)*(1/jwt) =-1/[(wt)^2]

This last equation describes the operation principle of the well known two-integrator oscillator: Two integrating stages with a total phase shift of -180 deg to be combined with an additional inverter stage.

This concludes my participation in this thread. In a technial discussion I don’t like formulations like (Quote Syncopator):
„Your magnanimity knows no bounds“.

Regards
LvW

 

[varunkant2k]

hey guyz,in the diagram there is ttl not gate given.i wanted to know in which configuration(CB,CE,CC) is the transistor Q2 connected and how to determine that.

CB,CE,CC are for small signal analysis. YOu please bound with followers. Which terminal follows your output.
Q2, both terminal are followed by outputs, Q3,and Q4. You may have understood by now that this Q2 works as collector and emitter follower by phase shifted.
In fact Q2 got the name as phase splitter. Once it drives Q4 and another phase it drives Q3.