1. The problem statement, all variables and given/known data Find the internal resistance seen at Vin. 2. Relevant equations 3. The attempt at a solution To solve the problem I started by ignoring the condensators and substituting the MOSFET by it's model. This resulted in the following circuit: By applying Thenevin's theorem it's possible to find the internal resistance. To do that I applied a test voltage source, VT, at the terminals and I proceeded to find an expression that relates VT with the current i that passes through it. By doing so I got to the result R = 2622 Ω. This appears to be wrong tho, since the solutions state that the resistance is 2.2kΩ. If someone could help me I'd appreciate. Thanks.