FET Amplifiers

Abstract

Amplifiers are probably the most useful of all electronic circuits. Let us look at some examples that demonstrate the need for amplifiers. When the electromagnetic energy that is radiated from a radio or television transmitter tower reaches a receiving antenna it induces a voltage across the antenna. This voltage has an amplitude measured in millionths of a volt (µV). In order to get the desired sound from a radio speaker or picture on a television screen it requires a signal amplitude in volts. Therefore we need some electronic circuit or circuits that can take an input waveform with an amplitude in microvolts and amplify it so that the output signal of the circuit has an amplitude measured in volts. Another example of the need for circuits that amplify voltage waveforms involves the use of transducers. These are devices that can be used to change one form of energy into a different kind. For most usable transducers the output is in the form of electrical energy. Some examples of these transducers are sound detectors or microphones, television cameras, heat detectors, nuclear detectors, strain gauges, solar cells, and other photoelectric devices. The output voltage that is obtained from many of these transducers is measured in thousandths of a volt (millivolt or mV). The output voltage from these must be amplified in order to make the desired uses of them.