AND Logical Gate

Visualizing the AND Logical Gate

The AND circuit is a simple way of showing how a circuit follows its truth table.

AND

According to the AND circuit truth table, when either of the inputs is off, then the line to one or both transistor bases is low voltage so the whole line is closed. So the base voltage for the third transistor (shown as a second part of the circuit) is at high voltage because is is closer to the battery pack than to ground. It is close to the positive voltage through the resister and thus at high voltage which opens the circuit of the transistor. This then allows the output to be connected to the ground (low voltage) giving the ultimate signal from the circuit as off.

When both of the input signals are at high voltage (high by our standards) this combined circuit is open and can conduct. So then the base of the other transistor is connected to ground (or low voltage) making that translator closed or off so the output line is closer to the high voltage of the battery pack and at our high(er) voltage level, so it signals on.

Colorful AND Truth Table

The AND Circuit Response

This does not require a lot of current flowing though our computer circuits. The reading of the circuits (the meaning of the circuits) depends on the voltage. Low voltage (from 0 - 1 volts) means off or 0 (zero); while high voltage (from 3.5 to 5 volts) means on or 1 (one).The transistors act like switches to turn the circuit on or off by regulating the voltage.

The Animated Computer

Dr. Jerome Heath