Digital logic, an Inverter or NOT gate Digital logic, an Inverter or NOT gate | Page 4

ABSTRACT
In digital logic, an inverter or NOT gate is a logic gate which implements logical
negation. The truth table is shown on the right.
An inverter circuit outputs a voltage representing the opposite logic-level to its
input. Its main function is to invert the input signal applied. If the applied input
is low then the output becomes high and vice versa. Inverters can be
constructed using a single NMOS transistor or a single PMOS transistor coupled
with a resistor. Since this 'resistive-drain' approach uses only a single type of
transistor, it can be fabricated at low cost. However, because current flows
through the resistor in one of the two states, the resistive-drain configuration
is disadvantaged for power consumption and processing speed. Alternatively,
inverters can be constructed using two complementary transistors in a CMOS
configuration. This configuration greatly reduces power consumption since one
of the transistors is always off in both logic states. Processing speed can also be