CS Stage with Diode-Connected Load
This circuit is evolved from the earlier circuit replacing the Resistor RD with a MOSFET, as it is difficult to fabricate resistors on SIlicon.
It can be observed that if the Gate and Drain of a MOSFET are shorted, it behaves like a small signal resistor.
This configuration is called as Diode Connected device.
As the Gate and the Drain are at the same potential (as they are connected together) the device operates in saturation region
Figure 4 shows the nMOS and pMOS diode connected devices.
Figure 5 shows the Small - Signal equivalent circuit