Input and output impedance

[goldcoin]

How do you calculate the input and output impedance for an electronic circuit (in general) ?

[Simon]

It's called thevenin's theorem: https://en.wikipedia.org/wiki/Th%C3%A9venin%27s_theorem

[goldcoin]

It's called thevenin's theorem: https://en.wikipedia.org/wiki/Th%C3%A9venin%27s_theorem

And if there are transistors in the circuit we replace them with small-signal/Ebers-Moll models and then apply Thevenin's theorem?

[tron9000]

http://wiki.analog.com/university/courses/electronics/text/chapter-9#output_impedance_current_follower_or_common_basegate_amplifier

example above

google is your friend...

[T3sl4co1l]

If you mean, of an arbitrary, truly general circuit, there need not be any single figure, nor does it need be computable at all!

Even for simple circuits, it can vary with voltage, time, internal configuration or state, etc.  And given those considerations, there are many (also non-unique) methods of averaging it, to get an equivalent value.

A classic example being an RF amplifier: the output capacitance of a transistor varies with voltage (both the supply or bias voltage, and the signal voltage), so that the matching impedance varies with voltage as well.  The best you can do is match the average (given a suitable averaging method), but even that is not very helpful, because it is only valid for one particular level.

If you have a fairly well-behaved, but otherwise unknown, circuit in a box (a "black box" experiment), and wish to measure its characteristics, then you can use a number of theorems to find this: you can use different load resistors or impedances to calculate the Thevenin equivalent, or the Norton equivalent, or a number of matrix-oriented methods that arise from the study of simple, abstract amplifier circuits or RF systems (e.g., the h, z and s parameters).

Tim

[goldcoin]

http://wiki.analog.com/university/courses/electronics/text/chapter-9#output_impedance_current_follower_or_common_basegate_amplifier

example above

google is your friend...

So in case of a common collector amplifier the input voltage is between the collector and base and the output voltage is the voltage drop between the collector and emitter ?

[LvW]

So in case of a common collector amplifier the input voltage is between the collector and base and the output voltage is the voltage drop between the collector and emitter ?

Yes - in, principle you are right. However, your wording sounds a bit "uncommon".
I think, it is more clear to say:
In a common-collector stage the collector node is grounded. Therefore,
* the input is between the base and ground,
* the output is between emitter and ground.

For measuring/simulating the corresponding resistances you simply need the corresponding voltage-to-current ratios.
Please note that for determining the output resistance it is necessary to inject a test current and to measure the voltage drop. And don`t forget to ground the signal input!   

[goldcoin]

So in case of a common collector amplifier the input voltage is between the collector and base and the output voltage is the voltage drop between the collector and emitter ?

Yes - in, principle you are right. However, your wording sounds a bit "uncommon".
I think, it is more clear to say:
In a common-collector stage the collector node is grounded. Therefore,
* the input is between the base and ground,
* the output is between emitter and ground.

For measuring/simulating the corresponding resistances you simply need the corresponding voltage-to-current ratios.
Please note that for determining the output resistance it is necessary to inject a test current and to measure the voltage drop. And don`t forget to ground the signal input!   

The common collector schematic shows the emitter resistor connected to ground and the collector connected to the positive voltage source. So the input is between base and emitter resistor and the output is between emitter and emitter resistor. That would mean that the emitter resistor is common to both input and output ?

[T3sl4co1l]

When speaking of AC signal analysis, supplies are ground.  The term used for this is: a supernode.

Tim

[LvW]

The common collector schematic shows the emitter resistor connected to ground and the collector connected to the positive voltage source. So the input is between base and emitter resistor and the output is between emitter and emitter resistor. That would mean that the emitter resistor is common to both input and output ?

The term "common collector" means:
The collector is a common node for defining input and output signals - and, as mentioned by T3sl4co1l - this applies to ac only (not DC). Therefore, the supply voltage represents an ac ground (zero source resistance).