双语chapter3.ppt

模拟电子学 授课教师：任爽 3.1 Introduction引言 3.1.1 The Contrast between Analog and Digital Electronics We have already explored how transistors and diodes are used as switching devices to process information which is represented in digital form. Digital electronics uses transistors as electrically controlled switches: transistors are either saturated or cut off. The active region is used only in transition from one state to the other. By contrast, analog electronics depends on the active region of transistors and other types of amplifiers. The Greek roots of “analog” mean “in due ratio”, signifying in this usage that information is encoded into an electrical signal which is proportional to the quantity being represented. In Fig.3.1 our information is some sort of music, originating physically in the excitation and resonance’s of a musical instrument. The radiated sound consists in the ordered movement of air molecules and is best understood as acoustic waves. These produce motion in the diaphragm of a microphone, which in turn produces an electrical signal. The variation in the electrical signal is a proportional representation of the sound waves. The electrical signal is amplified electronically, with an increase in signal power occurring at the expense of the input AC power to the amplifier. The amplifier output drives a recording head and produces a wavy groove on a disk. If the entire system is good, every acoustic variation of the air will be recorded on the disk and, when the record is played back through a similar system and the signal reradiated as sound energy by a loudspeaker, the resulting sound should faithfully reproduce the original music. Radio and TV broadcasting are common examples of analog systems, as are many electrical instruments used in monitoring deflection (strain gages, for example), motion (tachometers), and temperature (thermocouples). Many electrical instruments---voltmeters, ohmmeters, and oscilloscopes-utilize analog techniqu