An AND gate can have two or more inputs but only one output. Switches A and Bare two inputs of the gate and the bulb gives the output Y. The ON switch stands for logic input 1 and OFF switch stands for logic input 0. In this case, the bulb will glow only if it is connected to the supply voltage. This will happen only if both A and B switches are simultaneously ON (or 1).
The Boolean expression for the AND operation is represented as
Y = A.B = AB = A × B and read as A AND B.
The logic gate realized by using diodes is called a DDL Gate (Diode–Diode Logic Gate). The anodes of two diodes D1 and D2 connected in parallel are forward biased by a 5V battery through a 5 kΩ resistance. The output is taken from the anode.
Cathode wires A and B serve as input terminals. When either A or B or both the terminals are grounded, the respective diode will conduct and a potential drop will develop across the resistance and output will be 0.7 V, i.e. logic 0. When both the terminals are connected to 5V (for input 1, 1), neither of the diodes will conduct and output will be 5V, i.e. logic 1.