THE OPERATIONAL AMPLIFIER I began my project explaining some ideas about the operational amplifier; I have choosed this one because It's simple to manipulate, it usually takes the form of nothing more than an 8-pin dual in line, and its range of applications is immense. An operational amplifier is essentially multi-stage direct coupled amplifier.Operational amplifier were originally employed in the field of analogue computing and control systems, the first generation of such devices being based purely on discrete components. Due to various factors including the need to reduce the nose and drift inherent in high-gain direct coupled amplifier to an acceptable level,these devices were extremely costly. The symbol used for an operational amplifier is shown in fig.1 . It should be noted that the device has two signal input (labelled "+" and "-") one output operational amplifier generally require both positive and negative supplies, often between 9V, and 15V. Furthermore these supply connections are sometimes omitted from circuit diagrams and it is simply assumed that all devices are connected to the requisite common positive and negative supply rails ! PRACTICAL AMPLIFIER STAGE : Three basic practical operational amplifier circuits are shown in fig 1. fig 2. fig 3. each of these circuits employs negative feedback which is instrumental in reducing the voltage gain. All of this makes the operational amplifier very easy to use. Suppose ,for example we wish to make an inverting amplifier with a voltage gain of 100 to match an input resistance of one KO (kilohm). We simply make Rf equal to 100 KO and Rin equal to 1 KO. What could be more simple ! |
