# Transfer function trouble

## Main Question or Discussion Point

Hi everyone - I've been self-studying electronics for the past couple years and I have a confession to make: I'm terrible at deriving transfer functions. I'd really like to improve at it, but every time I see a circuit like the following (to analyze for Z parameters, for example) I start to panic. http://en.wikipedia.org/wiki/File:Smal-signal_mirror_circuit.png

Is some trick to go about analyzing a circuit like that? Or just draw up the nodes and try to grind it through with KCL? Any tips on how to get better at this important skill would be appreciated.

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berkeman
Mentor
Hi everyone - I've been self-studying electronics for the past couple years and I have a confession to make: I'm terrible at deriving transfer functions. I'd really like to improve at it, but every time I see a circuit like the following (to analyze for Z parameters, for example) I start to panic. http://en.wikipedia.org/wiki/File:Smal-signal_mirror_circuit.png

Is some trick to go about analyzing a circuit like that? Or just draw up the nodes and try to grind it through with KCL? Any tips on how to get better at this important skill would be appreciated.
There may be some tricks that can help, but I just knee-jerk go straight to the KCL equations.

The problem is with these two-port parameter things I never understand what to calculate - ok I understand I have to for example open circuit I2 in the example to find R21, but how do I calculate the voltage there if that node is open circuited? And what is I1 supposed to be? It's all really confusing. I'm sure if I could see a few worked examples it would make sense, but I don't have a textbook that covers this topic and I've searched the web for hours to no avail. Whatever I do, I can never seem to follow how those complicated expressions for the various parameters are obtained. :grumpy: