TRANSISTOR FUNCTIONS

a. Amplification. The transistor may be used as a current, voltage, or power amplifier. For instance, a stronger signal current may be obtained from a transistor (A, figure 16) than is fed into it. A signal of 1 milliampere fed into the input circuit of the transistor may be amplified to 20 milliamperes at its output. The amount of amplification depends on how the circuit is designed.
b. Oscillation. The transistor can be used in an oscillator circuit because it can convert direct current energy into alternating current energy.
When it is connected in an oscillator circuit, the transistor draws energy from a dc source and generates a dc voltage changing at an ac rate (B, figure 16).

c. Modulation and Demodulation. The transistor can be used in circuits that provide amplitude modulation (variation in amplitude of an RF signal) (A, figure 17) or frequency modulation (variation in frequency of an RF signal) (A, figure 18). Conversely, demodulation or detection of amplitude modulated signals (B, figure 17)  and frequency modulated signals (B, figure 18)  can also be accomplished with transistors. These circuits are well suited for miniature transmitters intended for short range applications.

d.  Miscellaneous. The transistor may also be used to change the shape of signal waveforms. Waveform shaping is vital in various types of radar, teletypewriter, computer, and television circuits. A, figure 19, shows how a transistor can be used in a circuit to change a sine wave into a square wave. B of the figure shows how a transistor can be used in a circuit to remove the negative or positive alterations of a series of positive and negative pulses.