Hi everyone, I am trying to learn about circuits from some slides I obtained and I am stuck on a slide. Here is a screenshot of it (it is in German): http://i.imgur.com/HCtWF.png It says: Example: Illustration of maximum achievable amplification of a MOSFET with the use of the parameters gm (transconductance) and gDS (output conductance). On the left is the circuit configuration. On the right is the effect of an input voltage change with x-axis drain voltage and y-axis drain current. It also has the derivation for the amplification. What confuses me is how they obtained: gm * ΔUGS + gDS * ΔUDS = 0 as a result of I0 being constant. Perhaps I am not understanding the graph completely. Can someone point me in the correct direction? For reference: gm = dID / dUG with UD const. gDS = dID / dUD with UG const. Many thanks.