Logic gates
Circuits such as the NOT gate in Figure 2.3 are so common in digital electronics that they are assigned schematic symbols to enable construction of higher-level diagrams representing more complex logic functions.
The symbol for a NOT gate is a triangle with a small circle at the output, shown in Figure 2.4:
Figure 2.4: NOT gate schematic symbol
The triangle represents an amplifier, meaning this is a device that turns a weaker input signal into a stronger output signal. The circle represents the inversion operator.
More complex logical operations can be developed by building upon the design of the NOT gate.
The circuit in Figure 2.5 uses two transistors to perform an AND operation on the inputs Input1 and Input2. An AND operation has an Output of 1 when both inputs are 1, otherwise the Output is 0. Resistor R2 pulls the Output signal low unless both transistors have been switched on by the high levels of the Input1 and Input2 signals...
