let's consider the equivalent circuit of a diode connected Mosfet.
Since the current source between drain and source is:
gm * Vgs = gm * Vds
and it is proportional to Vds, it means that this current source behaves like a resistor of value 1/gm.
Now I have two questions: - a diode connected Mosfet works in saturation, that means as a controlled source. How is it possible that it behave like a resistor (which is what will happen in triode region)? - Mosfets used as amplifiers need to be polarized in saturation in order to generate a current which is controlled by a voltage signal. So may be a diode connected Mosfet useful for an amplifier? Or is it just like a resistor and so unuseful for that aim?