Two port network

[Sambhav_1]

Hi,

In two port network we have four terminals and a black box and by defination the essential requirement known as the port condition in which the electric current entering one terminal must equal the current emerging from the other terminal on the same port.
I have a question that what kind of circuit should be place inside that black box such that this port condition is violated i.e the electric current entering one terminal is NOT equal the current emerging from the other terminal on the same port.

 

[barry]

Whaaaaat? You want a circuit that doesn't meet the fundamental requirement of a 2-port network, but you want to still call it a 2-port network. I'm afraid you can't have it both ways.

 

[danadakk]

Black box either / and has a real resistance / dissipation to heat or energy source / sink
in it.

REgards, Dana.

 

[FvM]

The question has no answer.

It cannot be determined if a pair of nodes meets the port condition by analysing the internal properties of the circuit itself. The port condition is dependent entirely on the external connections of the circuit. What are ports under one set of external circumstances may well not be ports under another.

Port (circuit theory) - Wikipedia

en.wikipedia.org

You should consider that port condition is no real circuit design issue rather an abstract problem of designing analysis setups. It depends on the type of circuit if the problem matters at all. E.g. in RF circuits you mostly have single ended ports with a ground terminal in each port. Respectively the port condition is automatically fulfilled. You can always enforce the port condition by driving ports through isolation transformers.

 

[AMS012]

It is impossible to have the current in and current out different. That will violate physics, kcl and everything. It is independent of what animal you have inside the two port network.

 

[FvM]

It is impossible to have the current in and current out different. That will violate physics, kcl and everything. It is independent of what animal you have inside the two port network.

It's well possible to violate the port conditions at a two port network. The case is discussed in detail in the above quoted Wikipedia link.

 

[AMS012]

It's well possible to violate the port conditions at a two port network. The case is discussed in detail in the above quoted Wikipedia link.

By the definition of two port network, current entering a terminal has to be equal to the current coming out of the other terminal on the same port. However, if you don't strictly stick to the definition, you can have the two currents to be different (like you mentioned in the case of some of the RF circuits interfacing with antenna etc.)

The bottom line is that, in any electric network/or be it mechanical network, the total sum of the energy (current) going out (or coming in) of all the individual terminals should add up to zero.

 

[barry]

Y

It's well possible to violate the port conditions at a two port network. The case is discussed in detail in the above quoted Wikipedia link.

Again, if the current out of the port Is not the same as the current in, then it is NOT, BY DEFINITION a two-port network. I can design black boxes for you all day that don't have current out the port equal to current into the port, but they’re not two-port networks.

 

[danadakk]

If one browses the web for mathematical definition of a two port network
ones gets all kinds pf constraints depending on the V,I relationships one
is trying to enforce with their specific mathematical relationships. So yes one can
define a two port to require current in one port lead to equal that coming
out. Or one can define two port to also have energy sources/sinks in it and the
defining equations have to be changed to meet the constraint imposed. Hence
currents can differ.

Its not just one specific implementation with one set of constraints. It can be
anything the author decides, with defining equations solving all possibilities
the author imposed on his two port internals. The two port can be non linear
as well. So one solves with a different equation approach. IEEE papers on this.

Unless the FDA has issued some new definition that we all must obey.....


Regards, Dana.

 

[FvM]

Again, if the current out of the port Is not the same as the current in, then it is NOT, BY DEFINITION a two-port network. I can design black boxes for you all day that don't have current out the port equal to current into the port, but they’re not two-port networks.

I suggest to take a look at the quote in post #4, and in case you don't see what it's talking about, also review the respective article.

I conclude that "violation of port condition" is a well defined term that has apparently an application in network theory. The article explains that meting the port condition is a combination of internal and external circuit. In so far, the idea of designing a violating black box misses the point.

On the other hand, I'd basically agree that a two-port-network with violated port condition is no useful analysis setup. As previously mentioned, I don't recognize a meaningful circuit design problem.

 

[barry]

I suggest to take a look at the quote in post #4, and in case you don't see what it's talking about, also review the respective article.

I suggest you follow the link in your referenced quote to the definition of a two-port network. I'll quote it here. Note the use of the word "essential". You can't ignore a requirement to justify your argument:

"Two terminals constitute a port if the currents applied to them satisfy the essential requirement known as the port condition: the electric current entering one terminal must equal the current emerging from the other terminal on the same port."

 

[FvM]

No interest in sophistic discussions

 

[barry]

No interest in sophistic discussions

You keep trying to argue an erroneous claim, and then when you can't defend it you accuse ME of sophistry?