ABSTRACT
Operational Amplifiers (usually called ‘op amps’) were originally made from discrete components, being designed to solve mathematical equations electronically, by performing operations such as addition and division in analogue computers. Now produced in integrated-circuit (IC) form, op amps have many uses, with one of the most important being as a high-gain d.c. and a.c. voltage amplifier. The main properties of an op amp include:
(i) a very high open-loop voltage gain Ao of around 105 for d.c. and low frequency a.c., which decreases with frequency increase
(ii) a very high input impedance, typically 106 to 1012 , such that current drawn from the device, or the circuit supplying it, is very small and the input voltage is passed on to the op amp with little loss
(iii) a very low output impedance, around 100, such that its output voltage is transferred efficiently to any load greater than a few kilohms
The circuit diagram symbol for an op amp is shown in Figure 18.1. It has one output, Vo, and two inputs; the inverting input, V1, is marked−, and the non-inverting input,V2, is marked+.
