Also see integrated circuit ( IC ).
A linear integrated circuit (linear IC) is a solid-state analog device characterized by a theoretically infinite number of possible operating states. It operates over a continuous range of input levels. In contrast, a digital IC has a finite number of discrete input and output states.
Within a certain input range, the amplification curve of a linear IC is a straight line; the input and output voltages are directly proportional. The best known, and most common, linear IC is the operational amplifier or op amp , which consists of resistors, diodes, and transistors in a conventional analog circuit. There are two inputs, called inverting and non-inverting. A signal applied to the inverting input results in a signal of opposite phase at the output. A signal applied to the non-inverting input produces a signal of identical phase at the output. A connection, through a variable resistance , between the output and the inverting input is used to control the amplification factor .
Linear ICs are employed in audio amplifiers, A/D (analog-to-digital) converters, averaging amplifiers, differentiators, DC (direct-current) amplifiers, integrators, multivibrators, oscillators, audio filters, and sweep generators. Linear ICs are available in most large electronics stores. Some devices contain several amplifiers within a single housing.