effect of Rg on gain of CS stage

[fly1]

If a resistance Rg is connected between gate and drain of a CS stage, how does it affect the gain of the MOSFET?

 

[The Electrician]

If the stage is then driven by a small signal voltage which has zero output impedance, the feedback through Rg will be shorted out by the source, and Rg will have no effect on the gain.

If the driving source has an output impedance greater than zero, then Rg will have an effect on the gain.

To determine just what the effect is, a small signal analysis can be performed.