When transistors are used in digital circuits they usually operate in
(A) active region
(B) breakdown region
(C) linear region
(D) saturation and cut off regions

Hint: The transistor can be used for various purposes like amplification, regulation of voltage, switching and signal modulation etc. In digital circuits, the transistor is used for the switching purpose. By using this information, we can obtain information about the operating regions of the transistor.


Complete step by step answer
The transistor is an essential part of the electronic devices. The transistor is a 3 terminal electronic device made of semiconductor material. Generally, silicon and germanium are used for the manufacturing of the transistor because they have to insulate as well as conducting properties.
We can use the transistor in the digital circuits to obtain switching operation. The current flow needs to be controlled in the digital circuits for better performance and desirable output. We can stop the current flow by switching off mode and flow the current by the switch on mode. For the switch on mode, the transistor must be in saturation region so that the efficient flow of current through the digital circuit can be achieved and for the switch on mode, the transistor must be in the cut off region, so that flow of current can be stopped in the digital circuits.
Therefore, when transistors are used in digital circuits, they usually operate in saturation and cut off regions and option (D) is correct.


Note: For the current control, the bipolar transistors are used for the switching purpose in the digital circuits. Depending upon the p-type and n-type semiconductor layers, the bipolar transistors are classified into two types, one is NPN transistor, and another one is PNP transistor.