Definition :

The AND gate is an electronic circuit that gives a high output (1) only if all its inputs are high. A dot (.) is used to show the AND operation i.e. A.B. Bear in mind that this dot is sometimes omitted i.e. AB.

"If both Inputs are true the Output will be true"

3 Input AND gate Truth table :

TTL AND gate :

TTL Logic gates are constructed by Transistor-Transistor Logic. Fig-2 shows a RTL- Resistor Transistor Logic. The TTL based AND gate ICs are as below :

• 74LS08 Quad 2-input
• 74LS11 Triple 3-input
• 74LS21 Dual 4-input

CMOS AND gate :

Three(3) p-type and three(3) n-type MOSFETs constructs a 2 input AND gate logic. The first 2 p-type and 2 n-type MOSFET construct a NAND gate logic and the rest two p-type and n-type construct an Inverter logic. So the first portion gives NAND output and the second part getting that output gives AND output doing the NOT logic operation (inverting) see the Fig-3. The CMOS type AND gates are shown below :

• CD4081 Quad 2-input
• CD4073 Triple 3-input
• CD4082 Dual 4-input

AND gate analogy :

Fig-4 shows an analogy of AND logic gate. Which constructed by a battery, 2-switches(SPST) and a electric bulb; where 2 switches are indicates AND inputs and the electric bulb as the AND output. If the switch A is closed and B is open the bulb will not light. If again switch A is opened and B is closed the output will be the same as previous, the bulb will not light. But if the both switches ( A and B) are closed the bulb will give light. That means this circuit follows the Truth table of an AND logic gate.