Definition :

The Logic NOR Gate or Inclusive-NOR gate is a combination of the digital logic OR gate with that of an inverter or NOT gate connected together in series. The NOR (Not - OR) gate has an output that is normally at logic level "1" and only goes "LOW" to logic level "0" when ANY of its inputs are at logic level "1". The Logic NOR Gate is the reverse or "Complementary" form of the OR gate we have seen previously.

"If the all Inputs are false the Output will be true"

3 Input NOR gate Truth table :

Transistor-Resistor NOR gate :

Fig-2 shows a RTL- Resistor Transistor Logic for NOR gate. Two Transistors and three Resistors can develop n NOR gate logic. The Bases of the two transistors are used as the inputs through the resistors and the both collectors jointly gives the NOR logic output. The TTL Logic gates are constructed by Transistor-Transistor Logic. The TTL based NOR gate ICs are shown below :

• 74LS02 Quad 2-input
• 74LS27 Triple 3-input
• 74LS260 Dual 4-input

CMOS NOR gate :

Two(2) p-type and two(2) n-type MOSFETs constructs a 2 input NOR gate logic. 2 p-type and 2 n-type MOSFETs construct a NOR gate logic. The pair of p-type and n-type FET's gates are jointly make inputs and out comes from where the two n-type FET's Drains and a p-type FET's source are connected. See the Fig-3. The CMOS type NOR gates are shown below :

• CD4001 Quad 2-input
• CD4025 Triple 3-input
• CD4002 Dual 4-input