Transistor Question ...

[IronMan79]

I would like to see if it is possible to mix two signals with one transistor: I don't have equipment to test it but would like to know at least theoretically what could I expect: I want to mix two signals and get some kind of mixed output, it doesn't matter how they are combined, just a random mix of the two signals.

 

So I though about injecting a signal into the Collector, a different signal into the Emitter and see what could come out of the Base terminal: I expect a very weak signal obviously since I am using the transistor not really as an amplifier but as some kind of mixing signal system, but the weak signal should be some kind of mix between the two signals injected into the Collector and Emitter, using the Base as an Output.

 

Would it work ? Could I expect to see some kind of mixing of the Signals ? Thanks for any advice or ideas...

[Xittenn]

As a topic over breakfast as I am waking up, sort of. Look up common base transistor configurations and replace V+ with a second class A positive signal. It will be less of a signal mixing or wave superposition as much as it will be a multiplier correct me if I'm wrong! It might be difficult for you to source material to help you through this topology because it is less common and more advanced in theory. I hope this helps get you started.

[Temporocitor]

It would be especially useful if you were able to delay, thus tell the two signals apart. If we compare the simple PNP transistor to a triode tube, the base is like the cathode, but either collector or emitter can regulate the flow. As for signals, I'm assuming we are taking monoplex signals as compared to multiplex (polyphonic in an audio amplifier.) Both could potentially be combined at either emitter or collector using the transistor as an SCR and 2 reactance circuits to control which signal is throughput.

[TonyMcC]

You should find this link useful:- http://www.radio-electronics.com/info/rf-technology-design/mixers/bjt-transistor-mixer-multiplier.php

[Externet]

The construction of your question shows very limited knowledge on how to use a transistor; to mix two signals, both should be fed to the properly biased base with large resistors in series at each and the transistor set to work as an amplifier, and the output taken from collector or emitter if low impedance is desired.

 

The simplest way to mix two signals is to use a transformer with 3 windings, one for mixed output and two for the inputs to be mixed. There is much more to consider depending on the properties of the signals.

[IronMan79]

I am not trying to solve any "problem", I am not trying to perform any "function", etc. I was just curious to know what happens if a signal is injected into the Collector and another in the Emitter and the base is used as an Output: I know that this is not "the way transistors are used", I know that you can mix signals in many other ways, etc (like injecting a signal in the Emitter and a different one in the Base and getting the Output from the Collector, etc. ), etc.

 

I was just wondering how a transistor would behave if you made it work "upside down" in a sense, just for "fun" and "curiosity".

 

I thing that you could expect a very weak signal out through the Base because of "leakage currents" and signals and such ?

[Xittenn]

I know that this is not "the way transistors are used"

 

Obviously not, because they are, and it is called a common base configuration and it finds special application.

[IronMan79]

From:

 

http://www.ilovephilosophy.com/viewtopic.php?f=4&t=178163

 

because a transistor is non linear, varying the voltages independently is not sufficient to determine the output

 

sure it'll work insofar as that you'll have a voltage at the base, and that it will vary at least weakly, but good luck extrapolating meaning from whatever that voltage is.. its been a few years since i've looked at this stuff lol

 

 

But, that is the subtle goal: the reason why I thought about it in the first place: the "destruction of meaning" or the "teasing of reality" so to say, just for fun (hence the reason why it is in philosophy forums in the first place ?).

 

Obviously not, because they are, and it is called a common base configuration and it finds special application.

 

 

Wrong Answer: tell me what could come out of the Base if it is used as the Output...

[TonyMcC]

Obviously not, because they are, and it is called a common base configuration and it finds special application.

Sorry, but in common base circuits the base is usually held at a fixed potential and the input(s) fed to the emitter to vary the current through the transistor. You don't therefore expect to find signal changes at the base. I suppose you might find small signals at the base of T1 in this 3 transistor circuit. However the capacitor C1 would tend to damp out these pretty effectively (IMO)

Edited February 14, 2012 by TonyMcC

[Xittenn]

Wrong Answer: tell me what could come out of the Base if it is used as the Output...

 

Ummmm common! :/

 

 

Sorry, but in common base circuits the base is usually held at a fixed potential and the input(s) fed to the emitter to vary the current through the transistor. You don't therefore expect to find signal changes at the base. I suppose you might find small signals at the base of T1 in this 3 transistor circuit. However the capacitor C1 would tend to damp out these pretty effectively (IMO)

 

That doesn't excuse it from being a common base topology.

 

 

I have no personal interest in this topic, so whoever wants to disagree can more than do so with little argument from me. I still stand behind my statements, but will now do so from over there. =====>

 

Transistors are a poor choice for philosophical debate and we are in engineering!

[TonyMcC]

Ummmm common! :/

 

 

 

 

That doesn't excuse it from being a common base topology.

 

 

I have no personal interest in this topic, so whoever wants to disagree can more than do so with little argument from me. I still stand behind my statements, but will now do so from over there. =====>

 

Transistors are a poor choice for philosophical debate and we are in engineering!

 

No offence meant, but I believe the statement in question was "I was just curious to know what happens if a signal is injected into the Collector and another in the Emitter and the base is used as an Output: I know that this is not "the way transistors are (generally?) used"".

 

The above statement is true as the following set of diagrams indicate:-

Edited February 14, 2012 by TonyMcC

[IronMan79]

No, I am not trying to solve any problem or trying to perform any function: I just wanted to know what could I expect if I use the transistor "upside down", just for fun, for curiosity, so the idea is to inject a signal in the Emitter and another different one in the Collector and see what would come out of the Base: of course this is not the way a transistor is configured, but that is exactly why I would like to know what could possibly come out of the Base. I imagine a very weak mixed (non linear ?) signal.. but I am just guessing...

 

It is just an experiment not an application....

[TonyMcC]

No, I am not trying to solve any problem or trying to perform any function: I just wanted to know what could I expect if I use the transistor "upside down", just for fun, for curiosity, so the idea is to inject a signal in the Emitter and another different one in the Collector and see what would come out of the Base: of course this is not the way a transistor is configured, but that is exactly why I would like to know what could possibly come out of the Base. I imagine a very weak mixed (non linear ?) signal.. but I am just guessing...

 

It is just an experiment not an application....

I'll try to give a sensible answer to a rather strange question. A bipolar transistor is a current operated device. If the transistor is operating with suitable bias the voltage difference between emitter and base will never go out of a very small range without either cutting off current flow through the transistor when the base/emitter voltage falls below about 0.5V or destroying the transistor if base/emitter voltage rises above about 0.7V. Consequently (IMO) If the transistor is conducting at all times and doesn't get destroyed you can expect the base voltage to closely follow the emitter voltage. If you are going to experiment then you better have a large supply of transistors!