ABSTRACT
The field of electronics includes many applications wherein important information is generated in the form of a voltage or current waveform. Often this voltage is too small to perform the function for which it is intended. Examples of this situation are the audio microphone in a sound amplification signal, the infrared diode detector of a heat-seeking missile, the output of the light intensity sensor of a CD player,
the output of a receiving antenna for an amplitude modulation (AM) or frequency modulation (FM) signal, the cell phone signal received by the base station before retransmission, and the output of a receiving dish antenna in a satellite TV system. Each of these signals have peak voltages in the range of hundreds of microvolts to hundreds of millivolts. To transmit a signal over phone lines or through the atmosphere and then activate a speaker or to illuminate a cathode-ray tube or other type of TV display may require a signal of several volts rather than millivolts. An audio amplification system may require peak voltages of tens of volts to drive the speaker.
The speakers in a CD system or in radio receivers may also require several volts to produce appropriate levels of volume. The video information for a TV signal may need to be amplified to a value of thousands of volts to drive the picture tube or display. Even in computer systems, the signals recovered from the floppy or hard disk drives must be amplified to logic levels to become useful. Amplification of each of these signals is imperative to make the signal become useful in its intended application. Consequently, amplifiers make up a part of almost every electronic system designed today. At the present time, the bipolar junction transistor (BJT) and the metal-oxide semiconductor field-
effect transistor (MOSFET) are the major devices used in amplification of electronic signals.
