Transistor Amplifiers University of Colorado （晶体管放大器科罗拉多大学）.pdf

Physics 3330 Experiment #7 Fall 1999 Transistor Amplifiers Purpose The aim of this experiment is to develop a bipolar transistor amplifier with a voltage gain of minus 25. The amplifier must accept input signals from a source impedance of 1 k and provide an undistorted output amplitude of 5 V when driving a 560 load. The bandwidth should extend from below 100 Hz to above 1 MHz. Introduction An electrical signal can be amplified by using a device which allows a small current or voltage to control the flow of a much larger current from a dc power source. Transistors are the basic device providing control of this kind. There are two general types of transistors, bipolar and field-effect. Very roughly, the difference between these two types is that for bipolar devices an input current controls the large current flow through the device, while for field-effect transistors an input voltage provides the control. In this experiment we will build a two-stage amplifier using two bipolar transistors. In most practical applications it is better to use an op-amp as a source of gain rather than to build an amplifier from discrete transistors. A good understanding of transistor fundamentals is nevertheless essential. Because op-amps are built from transistors, a detailed understanding of op- amp behavior, particularly input and output characteristics, must be based on an understanding of transistors. We will learn in Experiments #9 and #10 about logic devices, which are the basic elements of computers and other digital devices. These integrated circuits are also made from transistors, and so the behavior of logic devices depends upon the behavior of transistors. In addition to the importance of transistors as components of op-amps, logic circuits, and an enormous variety of other integrated circuits, single transistors are still important in many