Topic 48: The Source Follower and more Thevenin Analysis Techniques

In this video we will derive the voltage gain and output resistance equations for the class-A, common source amplifier. In order to derive the output resistance expression for the amplifier, more advanced Thevenin analysis methods are introduced. These methods are very general and are useful for analyzing circuits that contain dependent sources.

[@theoryandapplication7197]

interesting

[@leandrocarg]

Nice video. I developed a method using the loaded gain, that is calculate the gain including the load resistance. The output power will be (Av*Vin)^2/RL and since maximum power transfer is achieved when RL=Ro then we differentiate this expression and set to zero to solve for Ro, i.e.; 2*dAv/dRL(@RL=Ro)*Ro=Av(@RL=Ro) it looks complicated but usually is much faster to get the full analysis this way since if you let RL go to infinity in Av then you'll also get the actual unloaded gain, so two birds one shot.

[@leandrocarg]

There's one more method, when RL=Ro then the output voltage loaded will be half of the unloaded, so Av(unloaded)/2=Av(loaded@RL=Ro) and solve for Ro. This method is simpler because it doesn't require differentiation, though you still need to take the limit of the loaded gain as RL goes to infinity to get the unloaded gain.

[@Electronics4Guitar]

@@leandrocarg that’s a cool way to determine Ro. Sort of like using the Lagrangian formalism vs the Hamiltonian in a physics problem. You should put up a video explaining this technique.

[@leandrocarg]

@@Electronics4Guitar nice analogy. I don't make videos because my phone and PC are crap, maybe in the future. Your's are very good videos, very thorough and explicative, keep it up!