DIGITAL LOGIC - INVERTER

1.9 DIGITAL LOGIC - INVERTER

The inverter is a device which changes a logic 1 to a logic 0 or a logic 0 to a logic 1. The inverter can be shown in two different ways. An inverter used separately in a logic circuit is shown by a small triangle with a circle at either the input or the output. If the inverter is used with another logic device, only the circle is shown. Again it can be used at the input or the output of the logic device. The notation used to express this logic statement is C = and is read "C equals NOT A".

 Function

The function of an inverter can be represented most simply by a nor­mally de-energized relay. When there is an input at A, the relay will be energized causing the switch to be open and the output at C will be 0. When the input at A is 0, the switch is closed and there is an out­put at C.

 Truth Table

The various combinations of inputs using inverters and the resulting outputs are shown for the examples below.

Examples

The upper example shows inverters at both A and B and a corresponding sample circuit. Notation for this circuit is C =A.B and reads C equals "NOT A AND NOT B". The lower example shows an inverter only at B and a corresponding sample circuit. Notation for this circuit is

C = A+B and reads "C equals A AND NOT B".

Figure 1.5: Digital logic – INVERTER