Exp_7_fa09

Exp_7_fa09 - Physics 3330 Experiment #7 Fall 2009 Bipolar...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Physics 3330 Experiment #7 Fall 2009 Bipolar Transistor Amplifiers Purpose The aim of this experiment is to construct 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 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 . 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 current control. In this experiment we will build a two-stage amplifier using two bipolar transistors. In many 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. We will learn in Experiments #9 and #10 about digital electronics, including logic circuits and microcontrollers. These integrated circuits are also made from transistors. In addition to the importance of transistors as components of op-amps, digital circuits, and an enormous variety of other integrated circuits, single transistors (usually called “discrete” transistors) are used in many circuit applications. They are important as interface devices between integrated circuits and sensors, indicators, and other devices used to communicate with the outside world. High-performance amplifiers operating from DC through microwave frequencies use discrete transistor “front-ends” to achieve the lowest possible noise. Transistors are generally much faster than op-amps. The device we will use this week has a gain- bandwidth product of 300 MHz. The three terminals of a bipolar transistor are called the emitter, base, and collector (Figure 7.1). A small current into the base controls a large current flow from the collector to the emitter. The current at the base is typically 0.01 of the collector-emitter current. Moreover, the large collector current flow is almost independent of the voltage across the transistor from collector to emitter. This makes it possible to obtain a large amplification of voltage by having the collector current flow through a resistor. We will begin by constructing a common emitter amplifier , which operates on this principle. Experiment #7 7.1 Fall 2008
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
A major fault of a single-stage common emitter amplifier is its high output impedance. This can be cured by adding an emitter follower as a second stage. In this circuit the control signal is again applied at the base, but the output is taken from the emitter. The emitter voltage precisely follows the base voltage but more current is available from the emitter.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 11

Exp_7_fa09 - Physics 3330 Experiment #7 Fall 2009 Bipolar...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online