I have been studying about inverters for a while. In the book that I was reading, inverters have been explained according to the type of load connected to the drain of the driving transistors ie. resistive load, e-type nMOS load and d-type NMOS load.
In both of the above circuits, if a low input voltage is fed to the gate of the driving transistor the o/p will be high because current does not pass through the load or driving transistor and the o/p is simply Vdd.
When the input voltage is high current passes through the load and driving transistor and a low o/p is obtained because minimal voltage drop occurs in this case.
In neither of the above cases does having a load seems to be of any benefit.The loads seem to be simply contributing to power dissipation during linear mode operation and area . Why then are they connected in the first place?
Best Answer
If the bottom "driver" transistor is turned off, the output will just be disconnected from ground - it will not be high unless something, somewhere, pulls it high, and the load resistor or upper transistor will do this.
There are "open collector" or "open drain" gates that do omit the internal load, but when you use them, you have to add an external load, or depend on something else in the circuit to pull the output up.