Calculating input and output impedance of an amplifier

[uoficowboy]

I seem to remember a nice set of rules for calculating input and output impedance of an amplifier. Something like:

Treat all capacitors as opens, all voltage sources as shorts, all current sources as ... and then just calculate the resistance between input and ground. Or something like that.

Can anybody remind me of the rules?

Also, generally speaking, I think Ri = delta v/delta i. But what about Ro?

Sorry, it's been a while!

 

[Sean87]

@cowboy

Those rules applies for verylow and very high frequencies which capacitors can be thoouht as open or short...You have to be aware of frequency you are dealing with (If I remember correctly )