Experiment 11 - The Transistor Logic

Basically, all integrated circuits in digital electronics are based on transistor circuits. Can you recreate logical operations with transistors? In the following three experiments are you doing just that!

Consider an arbitrary logic unit on an Integrated Circuit (IC) with two inputs A and B and one output Q...

Circuit of a logic unit with two inputs. (Enlarge)

Circuit diagram for a logic unit with two inputs.

You control the inputs of the logic gate with the pushbutton switches S1 and S2...

• With open switches, the resistors R1 and R2 ensure that 0V is applied to the inputs. The logic gate interprets this as A = 0 and B = 0.
• If you press S1, at the input A +9V is applied and is interpreted as A = 1.
• If you press S2, B = 1.

The result Q is indicated by the LED.

• If the result is Q = 0, the output is 0V. The LED is dark.
• If the result is Q = 1, the output is 9V. The LED lights up.

In the next experiment, you replace the IC by a transistor circuit.