The bipolar junction transistor bjt is an active device. How a bjt bipolar junction transistor works its all in the doping the way a transistor works can be described with reference to fig. Alan doolittle lecture 20 bipolar junction transistors bjt. One can also make pnp bipolar junction transistors summary of i c as a function of v ce for a given i b. For the bjt to operate as an amplifier, the base emitter junction. Our objectives for todays lesson, are to introduce the bipolar junction transistor. Mar 15, 2020 as we will go through the topic, we will know about the transistor, mainly bipolar junction transistor or bjt. Bipolar junction transistor 1 by basic electronics.
Bipolar junction transistors learn about electronics. Lecture 7 bipolar junction transistors bjts guyeon wei division of engineering and applied sciences. Each junction can be forward or reverse biased independently. Bipolar junction transistors bjt general configuration and definitions the transistor is the main building block element of electronics. The bipolar junction transistor can be used as a switch. There are two junctions in bipolar junction transistor. The bjt has two pn junctions, the base emitter junction and the base collector junction. Because of this, such junctions are very useful for operation at the frequencies as high as 10 ghz. Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. One pn junction of a transistor is reversebiased, whereas the other is forwardbiased. In this lecture, well introduce one of the fundamental analog devices. In summary, during this lesson i introduced the bipolar junction transistor. A bipolar junction transistor bipolar transistor or bjt is a type of transistor that uses both electrons and holes as charge carriers. Bjt bipolar junction transistor are widely used an amplifier, oscillator, switch etc.
A very common one is the bipolar junction transistor or bjt. Bipolar junction transistor 8 typical operation of junction transistor amplifier typically the collector current, ic, is 100 to times greater than the base current ib, depending on the type of transistor used if we take the base current ib as an input and the collector current ic as an output, then we can say that. Moreover, a gradual change or grading of the material is possible within each region. Analog circuits video course course outline this course is an introduction to amplifiers using transistors. As we will go through the topic, we will know about the transistor, mainly bipolar junction transistor. Bjt bipolar junction transistor construction, types and. The fusion of these two diodes produces a three layer, two junction, three terminal device forming the basis of a bipolar junction transistor, or bjt for short. We have seen how the isolation between the transistors have to be. Module 3 bipolar junction transistors semiconductors module 3 pdf 3 e. This name is a representation for a device having transfer resistors. Bipolar junction transistors solidstate device theory. Lecture series on electronics for analog signal processing i by prof.
One way to look at a bjt transistor is two backtoback diodes, has very different characteristics. Haileselassie and kou vue 111420 elc eng 330 electronics i fall 201 2. Since bipolar junction transistor is a threeterminal device, there are three ways to connect it within an electric circuit while one terminal is the same for both output and input. Bipolar junction transistors the transistor is a threelayer semiconductor device consisting of either two n and one p type layers. Bipolar junction transistor bjt few most important applications of transistor are. Electronic fundamentals i page 71 the bipolar junction transistor the bjt is a three terminal device whose output current, voltage and power are controlled by its input in communication systems, the transistor is used as the primary component in an, a circuit that is used to increase the strength of an ac signal. The purpose of this laboratory is to become familiar with the d. A bipolar junction transistor bjt consists of three differently doped re gions. Bjts are of two types namely npn and pnp based on doping types of the three main terminals. Power bipolar junction transistor bjt background the bipolar junction transistor was invented in 1947 by shockley, brattain, and bardeen.
The point contact junction has very low value of the capacitance. And the saturation current is a very small number, typically about 1 times 10 to the minus 15 amps. In bipolar junction transistor, electric current is conducted by both free electrons and holes. Transistor fundamentals transistor developed in december 23, 1947 in bell laboratories by john bardeen, william shockley, and walter brattain basically a resistor that amplifies electrical impulses as they are from its input to its output terminals basic types bipolar junction transistor. The operation of the transistor is very dependent on the degree of doping of the various parts of the. Collector npn transistor pnp transistor p n p n p n. Contacts are made to all three regions, the two outer regions called the emitter and collector and the middle region called the base. The famous and commonly use of this device is bjts bipolar junction transistors. Bipolar junction transistor working, definition, application. Bipolar junction transistor bjt npntransistor pnptransistor bjt is a 3 terminal device. The very first bipolar junction transistors were fabricated from a bar of germanium with two closely spaced alloyed contacts. Remember, the diode consists of a single pn junction with a circuit schematic symbol that looks like this.
As we have seen a semiconductor offer less resistance to flow current in one direction and high resistance is another direction and we can call transistor. In this section, you will see how semiconductive materials are used to form a bjt, and you will learn the standard bjt symbols. Electronics tutorial about the bipolar transistor also called the bipolar junction transistor or bjt including the transistor. A bipolar junction transistor or bjt is a three terminal electronic device that amplifies the flow of current. Emitter is heavily doped, collector is moderately doped and base is lightly doped and base is very thin. Bipolar junction transistors types of bipolar junction transistors. Electronic fundamentals i page 71 the bipolar junction. The difference is the polarity of the base emitter diode junctions, as signified by the direction of the schematic symbol emitter arrow. Since bipolar junction transistor is a threeterminal device, there are three ways to connect it within an electric circuit while one terminal is the same for both output and. Bipolar junction transistors bjts questions and answers q1. Unipolar transistors, such as fieldeffect transistors, use only one kind of charge carrier. The bipolar junction transistor bjt is constructed of three regions.
Bipolar junction transistor physics and radioelectronics. Every method of connection responds differently to the input signals within a circuit. The word transistor is derived from the words transfer and resistor it describes the operation of a bjt i. Introductionintroduction the basic of electronic system nowadays is semiconductor device. Explain why an ordinary junction transistor is called bipolar.
The invention of the bipolar transistor in 1948 ushered in a revolution in electronics. Introduction to bipolar junction transistor bjt youtube. One way to look at a bjt transistor is two backtoback diodes. This type of transistor is called bipolar because both electrons and holes are used to carry charges through the npn or pnp junction.
This is my pnp bipolar junction transistor, ok and i also have an npn bipolar junction transistor. Bipolar junction transistors tlt8016 basic analog circuits 20052007 9 example 4. Bipolar junction transistor bjt switch analog electronics. Bipolar junction transistors transistor operation the biasing of the two types of transistor has been illustrated in the figures. It is a semiconductor device and it comes in two general types. The type of transistor just described is a npn bipolar junction transistor schematic symbol. Contacts are made to all three regions, the two outer regions called the emitter and. How to use bjt bipolar junction transistor beginners. Nov 28, 2015 presentation on bipolar junction transistor slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Germanium was used since it could easily be purified such that the minority.
Bipolar junction transistorbipolar junction transistor bjtbjt chapter 3 2. Typically a thin wafer of germanium was used for the base of the. While the forward active mode of operation is the most useful bias mode when using a bipolar junction transistor as an amplifier, one cannot ignore the other bias modes especially when using the device as. As a result, the energy bandgap as well as all other material properties can be different in the emitter, base and collector. Multiple choice questions and answers on transistors. These can have the configuration of npn or pnp and the various layers can either be. Thus a jucntion transistor is formed by sandwiching a thin layet of ptype semiconductor between two layers of ntype semiconductor and vice versa.
It is a currentdriven device mosfet is voltage driven, the output current is equal to the input current times a factor which is called gain. A bipolar junction transistor consists of two backtoback pn junctions, who share a thin common region with width, w b. An npn transistor consists of two semiconductor junctions that have a thin pdoped anode region and pnp transistor also consists of two semiconductor junctions that have a thin n doped cathode region. The base current i b controls the collector current i. Bjts are of two kinds pnp transistor and npn transistor.
Lecture notes microelectronic devices and circuits electrical. The middle section base is narrow and one of the other two regions emitter is heavily doped. Radhakrishna rao, department of electrical engineering,iit madras. Though initially it was called the solid state version of the vacuum triode, the term transistor has survived. The early voltage va has a typical value of 150 volts. The multifold advantages of replacing vacuum tubes with a solidstate device rapidly promulgated its use in applications. As we have seen a semiconductor offer less resistance to flow current in one direction and high resistance is another direction and we can call transistor as the device mode of the semiconductor. Bipolar junction transistors bjt transistor basics a bipolar junction transistor is a three layer npn or pnp semiconductor device. We present a comparison of these two in figure below.
Bipolar junction transistor 1 introduction to bipolar junction transistors transistors are three port devices used in most integrated circuits, such as amplifiers transistors are active components recall that resistors, capacitors and inductors are passive there are two types of transistor. Bipolar junction transistors bjt and its applications. The availability of singlecrystal silicon technology with higher purity levels together. Bipolar junction transistors emitter p n collector base pnp transistor emitter n p base npn transistor bipolar. Bipolar junction transistors are available as pnp as well as npn devices. If you continue browsing the site, you agree to the use of cookies on this website. Let us start our discussion of the bipolar junction transistors or the bjt in short. These transistors are also known as bipolar junction transistor bji and are our subject of study in this section. The base current i b controls the collector current i c regions of bjt operation. Here we will describe the system characteristics of the bjt. As we have seen a semiconductor offers less resistance to flow of current in one direction and high resistance in another direction, we call the device made of semiconductors as a transistor. We will begin looking at transistors with the bipolar junction transistor. And for reference, i have drawn the structure of a pn junction diode.
The three layers are called the emitter, base and collector. In this video, the bipolar junction transistor, its different region of operation, different configurations and the working is briefly explained. Because the transistor operation is carried out by two types of charge carriers majority and minority carriers, an ordinary transistor is called bipolar. In this first transistor lecture, well spend time applying our familiar semiconductor. The bipolar junction transistor can be considered essentially as two pn junctions placed backtoback. Technical feats previously requiring relatively large, mechanically fragile, powerhungry vacuum tubes were suddenly achievable with tiny, mechanically rugged, powerthrifty specks of crystalline silicon. We will spend some time understanding how they work based on what we know about pn junctions. Introduction to bipolar junction transistors bjt bipolar. In this picture, i c is independent of v bc and v ce as long as v be v t i c i s e 0. This is required when the typical digital output max current output 20ma does not provide sufficent current drive for high current devices like lamps, solenoids or motors.