measuring

the output impedance in a circuit. Take a look to this

(www.eurobotics.org/vco/circuito.doc) simple circuit. When I meassure

the

output impedance using the convencional way, that is, using a voltage

source

at the output while shortcutting the dependences ones I get 6 MOhmns. If

instead of this I use feedback techniques to calculate the output

impedance I

get 30 GOhmns... What is going on?.

If transistor is a Mosfet.

When I meassure the output impedance using the convencional way, that is, using a voltage source

at the output while shortcutting the dependences ones I get 60 GOhmns. If

I use feedback techniques to calculate the output

impedance I

get 60 GOhmns.

when I work with BJT the values are different.

What happen with rpi and ru?

Thank you all.