How to calculate the input impedance?

[kingswan]

Hello, I am a newbie of IC. And these days, I really confuse about the "input impedance". According to TWO-PORT,
for a VCVS, we should open the output to calculate the input impedance, and for a VCCS, we should short the
output to calculate the input impedance. But for a OPAMP or OTA, should I open or short the output, or it depends?

We know that a MOSFET is a VCCS, but for a Common-Source or a Common-Gate configuration, the load resistor
transfer the output current to output voltage. So should treat it like a VCVS or VCCS? I use small-signal
analysis. And for CS or CG, whatever I short or open the output, I get the same result of input impedance.

But for Common-Drain (source follower), problem is coming. Only I open the circuit, I can get the same result
with GRAY's book. And In GRAY's book, when he refer to the CD configuration, he doesn't talk about the Gm of CD,
is that CD is a VCVS, so I should open the output to get the input imdedance? But how about CS nad CG, are they
VCVS or VCCS? And can I decide a circuit is a VCCS or VCVS?

Where I get something wrong? I know maybe my description is a mess. But I deeply hope that somebody can get my
point and kindly help me to solve the problems.

Thank you very much!

Kingswan