THE NOT GATE

• It is so called because its output is NOT the same as its input.
• It is also called an inverter because it inverts the input signal.
• It has one input and one output.
• The schematic symbol for inversion is a small circle.
• The logical symbol for inversion is a bar over the function to indicate the opposite state.

BUBBLED GATES

• It’s inputs are NOTed or inverted.
• Here is the example of an AND gate whose both inputs are inverted.
• The bubbles acting as a reminder of the inversion or complementation that takes place before ANDing the inputs.
• A bubbled AND gate is equivalent to a NOR gate.

THE NOR GATE

• Actually it is a NOT- OR  gate.
• An OR fate y connecting an inverter in its output.
• The output equation is
• A NOR function is just the reverse of the OR function.
• The output of NOR gate is 1 when all its inputs are 0.
• So the output is true only when all inputs are false.

THE NOR GATE IS A UNIVERSAL GATE