So I have this VCO for which I'm trying to calculate the characteristic equation for, vo/vi. Image of this and the small circuit equivalent attached. I've also attached a simpler (in my opinion) common-source small signal equivalent to express that representation of the output, for instance, is rather intuitive in this case. We see an equivalent impedance (parallel resistors) with a current through them (negative polarity relative to Vo). In other words, I can't intuitively understand what is going on in the common-drain case. We have an equivalent impedance at the output (R parallel with C2), but there is a transversal component, C1, which is throwing me off badly. I suppose I'm looking for key words or hints that may give me a little more insight into this calculation. Some specific questions: -Is our input here (Vi) Vg or Vgs? -The output (Vo) I would call Vs, or similarly Vsd since the drain is (dynamically) grounded.