John said:

The OP doesn't understand Thévenin and you want to sell him Laplace? Is

this just an ego trip or do you really not understand the KISS

Principle?

No not KISS. Didn't you read my OP? I wanted to go passed the simple

cases that everyone talks about and delve deaper. I was taught the

calculation method for input impedances and have used it before but

then I started questioning how voltage and current sources would be

dealt with. Then I realized that I could make circuits (like the

simple one I posted) that would not have a contast Vin/Iin ratio. This

is why I wanted a more STRICT definition of input impedance.

Although I'm a Computer Science student, I do understand Thevenin and

Laplace from my EE course. Thevenin applies to output impedances, and

the method has specific treatments for voltage/current sources when

looking BACK into a circuit. But I always wondered the method required

to treat voltage and current sources for looking INTO a circuit (INPUT

IMPEDANCE). V/I for this circuit is not constant, but other posters

have noted that in such a case we only worry about the incremental

effect on I for each Volt (which is the same result you get if you

short voltage sources and open current sources - much like when

calculating Thevenin output impedances).

I hope the Laplace definition of impedance and previous example have

helped you. It is correct for input impedances, output impedances, and

anything in between. It also works for active voltage/current sources, as

the example illustrates. Ratch