MOSFET common source amplifier. Current source increases the gain of this circuit, with a resistor load in the drain the maximum gain is quite limited due to the MOSFETs inherently low transconductance. A current source has a very high impedance with AC signals, this high impedance allows the MOSFETs low transconductance to make a reasonable amount of gain, in this case around X100
If you want to build this circuit a current source can be made using a jfet and a resistor. Don't know why jfets aren't available on this app.
