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