May 2021 StudentZone Quiz Solution

Questions:

  1. Can you briefly describe two ways in which the gain of the source follower can be improved (closer to one)?

Answers:

Looking at the gain equation for the source follower circuit:

We can observe that there are to parameters which the gain is dependent on. Therefore, the two alternatives to get a closer to ideal gain (A = 1) are:

  • Decrease the rS value, by increasing ID (not preferable due to the dependance between ID and RL).
  • Increase the value of RL – source load resistor (this can be achieved by adding a current mirror circuit instead of the source load resistance, which provides a constant current ID and a high output resistance, increasing the value of RL)