Electronic Design and Application

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Electronic Design and Applications

Bipolar Junction Transistor and Operational Amplifiers

Introduction

In 1904-1947, a vacuum tube was the electronic device of development and interest. In the year 1904, the vacuum tube diode was introduced by J.A. Fleming. Thereafter in 1906, Lee De forest added a the third element called the control grid, to the vacuum diode resulting in the first amplifier called the triode.

A transistor is a three layer semiconductor device consisting of either two n- or one p- type layers of material or two p- and one n-type layers of material. The first one is called an npn transistor while the other is called a pnp transistor. Bipolar junction transistor is a three-terminal device constructed of doped semiconductor material and can be used in amplifying or switching applications. It is called “bipolar” because its operation involves both electrons and holes participating in the injection process of oppositely polarized material. The diagram below shows the two types of bipolar transistors:

The terminals above indicated by capital letters means C for collector, E for emitter and B for base.

Biasing is the process of applying an external voltage across two terminals in order to get a response. Biasing of the common-base configuration in the active region can be determined easily by using the fact that Ic is approximately equal to Ie and also assuming that Ib is approximately equal to 0μA. A direct current (DC) supply can be inserted with a polarity that will support the resulting current direction. With regards to the npn transistor, it will have to be reversed.

A common emitter is part of an electronic amplifier stage based on a bipolar transistor connected in series with a load element such as a resistor. A bipolar junction transistor can also be connected to form a single amplifier in the common emitter configuration

It is can also be called the common emitter configuration because the emitter is common to both the input and output terminals. The output characteristics is the plot of the output current (Ic) against the output voltage (Vce) for different values of Ib. The input characteristics is the plotting of the input current Ib against the input voltage Vbe for different values of the output voltage Vce. It is important to note that in the active region of a common- emitter amplifier, the base- emitter junction is a forward-biased whereby the collector-base is reverse biased.

An operational amplifier is a DC coupled high-gain amplifier with differential inputs and sometimes a single output. The output of an operational amplifier is controlled by negative feedback because the amplifier’s high gain mostly determines the output voltage for any given input. An operational amplifier can be constructed by fabricating all the necessary components on single chip of silicon to form a monolithic integrated circuit. Operational amplifiers have a very high input resistance and a low output resistance. It also has a very high gain. For these reason mentioned above, operational amplifiers are extremely useful in constructing other range of circuits and not just amplifiers.

There are different types of amplifiers such as:

  1. A non inverting amplifier
  2. An inverting amplifier
  3. A unity gain buffer amplifier
  4. A current to voltage converter
  5. A differential amplifier (subtractor)
  6. An inverting summing amplifier (adder)
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And etc

Learning Objectives

  1. To understand how to use Multisim.
  2. This experiment will help me to understand the output characteristics of a bipolar junction transistor.
  3. To understand the input characteristics.
  4. Will help to understand transistor biasing.
  5. To check bias condition.
  6. How to set up instruments and measuring the gain.
  7. The effect of load variation.
  8. The frequency response.
  9. The effect of Ce.
  10. To understand the functions of different types of amplifiers.

Background theory

Bipolar junction transistor can be used ...

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