TABLE OF CONTENTS Linear ICs are single-chip arrangements of amplifier circuits that are intended to be biased and operated in a linear way. This definition is usually extended to include ICs that have a comparatively slow switching action controlled by an approximately linear charge and discharge of a capacitor, such as the 555 timer.
The most important class of linear amplifier IC is the operational amplifier ( op-amp) which features high-gain, high-input resistance, low-output resistance and DC coupling internally. Such amplifiers whose typical pinout and symbol are illustrated in Figure 6.1 are almost invariably used in negative feedback circuits, and make use of a balanced form of internal circuit so that power supply hum and noise picked up by stray capacitance are both discriminated against.
As an illustration of the internal circuit techniques that are used, Figure 6.2 shows the internal circuitry of a typical old model of linear IC, the 741 operational amplifier, which is still in production. The circuit is basically that of an elaborate balanced DC coupled amplifier using 20 transistors. One feature, very common in linear ICs, is the use of a current mirror as part of the circuit. The principle of a current mirror is that a current fed in at the input of the current mirror circuit will produce an identical value of current in the second. The circuit is used...
