OR gate (CMOS: NOR + inverter)

Objective

Build OR from a NOR followed by an inverter (six transistors).

Procedure

1. Use the Controls tab (or the batteries' Properties) to set each input to 0 V or 5 V and press Start Simulation; turn Live on and drag an input slider to watch the output.

Theory

OR = NOT(NOR).

Questions to answer

1. How many transistors does an OR gate need compared with a NOR?

Components used

3 × 2N7000 N-MOSFET, 3 × BS250 P-MOSFET, 3 × Battery / DC source, LED 5mm Red, Panel voltmeter, Resistor 220 ohm 1/4W

About the model

Ideal wires; component models as listed in the catalogue (no parasitics, no temperature drift). Built without a breadboard so the schematic stays readable.

More Logic Gates from Components experiments

• XOR gate (four CMOS NAND gates)
• Half adder from CMOS NAND gates
• Full adder from nine CMOS NAND gates
• SR latch (bistable multivibrator from two transistors)
• Astable multivibrator (two-transistor oscillator, LED flasher)