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ME 6405 Student Lecture Transistor

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1 ME 6405 Student Lecture Transistor
Sung-bum Kang Keun Jae Kim Hongchul Sohn Wenwei Xu October 1, 2009 Georgia Institute of Technology

2 Contents Introduction to Transistor Bipolar Junction Transistor
1 Introduction to Transistor (Speaker: Sung-bum Kang) 2 Bipolar Junction Transistor (Speaker: Keun Jae Kim) 3 Field Effect Transistor (Speaker: Hongchul Sohn) 4 Power Transistor (Speaker: Wenwei Xu) 5 Applications of Transistor (Speaker: Wenwei Xu)

3 “Transistor” Part 1 Introduction to Transistor
(Speaker: Sung-bum Kang) 2 Bipolar Junction Transistor (Speaker: Keun Jae Kim) 3 Field Effect Transistor (Speaker: Hongchul Sohn) 4 Power Transistor (Speaker: Wenwei Xu) 5 Applications of Transistor (Speaker: Wenwei Xu)

4 Amplifier and Electronic Switch are needed.
Introduction Question #1: How can we transfer original signal in long distance without loss? Question #2: How can we control the TV with remote-controller? Question #3: How can a computer recognize 0(off) and 1(on) for computing? Amplifier and Electronic Switch are needed. Amplifier: any device that changes, usually increases, the amplitude of a signal. Electronic Switch: switch that the physical opening and closing is achieved by applying appropriate electrical control signals.

5 Transistor solved this problem.
Introduction Early 20th century, vacuum tube was used for the amplifier and switch. ENIAC, the first general-purpose electronic computer, contains 17,468 vacuum tubes. Vacuum Tube Radio However, Vacuum Tube is too big, fragile, and energy-consuming. Transistor solved this problem.

6 Introduction – Invention of Transistor
In 1947, John Bardeen, Walter Brattain, and William Schockly, researchers at Bell Lab, invented Transistor. They found Transistor Effect: “when electrical contacts were applied to a crystal of germanium, the output power was larger than the input.” In 1956, they were awarded the Nobel Prize in physics. Transistor is a semiconductor device commonly used to amplify or switch electronic signals. John Bardeen, Walter Brattain, and William Schockly First model of Transistor, 1947

7 Introduction – Progress of Transistor
1941, Vacuum Tube Edison effect 1948, the first (Germanium) TR John Bardeen, Walter Brattain, and William Schockly 1954, Silicon TR At TI Lab, Ease of processing, lower cost, greater power handling, more stable temperature characteristics 1958, Integrated Circuit Now? Circuits based on individual transistors became too large and too difficult to assemble. To make the circuits even faster, one needed to pack the transistors closer and closer together. In 1958 the integrated circuit was developed at Texas Instrument. Instead of making transistors one-by-one, several transistors could be made at the same time, on the same piece of semiconductor. Not only transistors, but other electric components such as resistors, capacitors and diodes could be made by the same process. For more than 30 years, since the 1960's, the number of transistors per unit area has been doubling every 1.5 years based on Moore's law. Latest technology is 2nm silicon wafer. Intel CEO Paul Otellini introduced it last Tuesday. This wafer can contain more than 2.9 billion TRs into an area of fingernail. Individual electronic components were soldered on to printed circuit boards. IC placed all components in one chip. Sep 2009, 22nm silicon wafer more than 2.9 billion transistors is packed into an area of fingernail Intel CEO Paul Otellini, Sep

8 Introduction – Underlying Science
Semiconductor is a basic building material of most integrated circuits. is a material that has an electrical resistivity between that of a conductor and an insulator. has a few charge carriers(holes or free electrons) and may hence be classified as almost insulator. However, the conductivity increases by adding impurities(doping). In semiconductors, current can be carried either by the flow of electrons or by the flow of positively-charged "holes" in the electron structure of the material. Silicon is used in most commercial semiconductors

9 Introduction – Underlying Science
Doping P(positive)-type doping is adding a certain type of atoms to the semiconductor in order to increase holes. P-type semiconductor, acceptor N(negative)-type doping is adding some amount of an element with more electrons in order to increase free electrons. N-type semiconductor, donor Add Group V (Phosphorous) Add Group III(Boron)

10 Introduction – Underlying Science
PN Junction is a junction formed by P-type and N-type semiconductors together in very close contact. What happens at the junction? Electrons(+) from n(-) region diffuse to occupy holes(-) in p(+) region. Thin depletion region forms near junction. Let’s suppose the situation there are two rooms. At the left room, there are many single girls and at the right room, there are many single boys. If this junction is a gate, the boys at near the gate might be try to enter the girl’s room to find his darling. After a while, this region will be filled with several couples and they will block the gate. And the remained boys cannot go through the crowded couples. Unfortunately, they have to live alone forever.

11 Introduction – Underlying Science
Forward bias -V pumps electrons into the N-region. +V pumps more holes into the P-region. Excess of charge in P and N region will apply pressure on the depletion region and will make it shrink. → current flows External Energy Backward bias -V sucked out electrons from N-region. +V sucked out holes from P-region. The depletion layer widens and it occupies the entire diode(p-n). → current doesn’t flow

12 Introduction – Types of Transistor
Transistor are categorized by Semiconductor material: germanium, silicon, gallium arsenide, etc. Structure: BJT, FET, IGFET (MOSFET), IGBT Polarity: NPN, PNP (BJTs); N-channel, P-channel (FETs) Maximum power rating: low, medium, high Maximum operating frequency: low, medium, high Application: switch, audio, high voltage, etc. Physical packaging: through hole, surface mount, ball grid array, etc. Amplification factor Various Types of Transistor: General Purpose Transistors Bipolar Junction Transistor (BJT) Field Effect Transistors (FET) Power Transistors

13 “Transistor” Part 2 Introduction to Transistor
1 Introduction to Transistor (Speaker: Sung-bum Kang) 2 Bipolar Junction Transistor (Speaker: Keun Jae Kim) 3 Field Effect Transistor (Speaker: Hongchul Sohn) 4 Power Transistor (Speaker: Wenwei Xu) 5 Applications of Transistor (Speaker: Wenwei Xu)

14 BJT Introduction NPN PNP 3 Terminals 2 Types: NPN, PNP Base (B)
Collector (C) Emitter (E) 2 Types: NPN, PNP Currents flow in opposite direction NPN: BE forward biased BC reverse biased PNP: BE reverse biased BC forward biased PNP

15 BJT Characteristics iE = iC + iB iC = βiB VBE = VB – VE VCE = VC - VE
IC is controlled by IB (Current Control) β (beta) is amplification factor for transistor Typical value of is β 20 ~ 200 iE = iC + iB iC = βiB VBE = VB – VE VCE = VC - VE Georgia Institute of Technology

16 BJT Operating Regions Operating Regions
16

17 BJT Operating Regions Operating Regions Operating Region Parameters
Mode Cut Off VBE < Vcut-in VCE > Vsupply IB = IC = 0 Switch OFF Linear VBE = Vcut-in Vsat < VCE < Vsupply IC = β*IB Amplification Saturated VBE = Vcut-in, VCE < Vsat IB > IC,max, IC,max > 0 Switch ON 17

18 BJT Operating Regions Cutoff Region: Active / Linear Region:
VBE < Vcut-in, iB = iC = 0, VCE > Vsupply Active / Linear Region: VBE = Vcut-in, iB > 0 iC = βiB, Vsat < VCE < Vsupply Saturation Region: VBE = Vcut-in, iB > iC,max iC,max, VCE < Vsat Vsupply Vin Georgia Institute of Technology

19 BJT as Amplifier Question: What is the minimum Vin that can use the transistor as an amplifier? Vsupply – iC *RC – VCE=0 Given: RB = 10 kΩ RC = 1 kΩ β = 100 VSupply = 10 V Vcut-in = 0.7 V Vsat = 0.2 V iC = (Vsupply – VCE) / RC Set VCE = Vsat = 0.2V iC = (10 – 0.2) / 1000 = 9.8mA iC = βiB iB = iC / β = /100 = 0.098mA VSupply Vin RB RC Vin - iB*RB – VBE = 0 Vin = iB*RB + VBE Set VBE = Vcut-in = 0.7V Vin = 0.098*(10-3)* V Vin = 1.68V or greater. 19

20 BJT as Switch From 3rd Exercise Turns on/off coils digitally
Spring 2007 Power Point Slides As seen in Exercise 3 that we did some weeks ago, the transistor acts as a switch either being fully open or fully closed upon the port on the chip being logic high or low.

21 “Transistor” Part 3 Introduction to Transistor
1 Introduction to Transistor (Speaker: Sung-bum Kang) 2 Bipolar Junction Transistor (Speaker: Keun Jae Kim) 3 Field Effect Transistor (Speaker: Hongchul Sohn) 4 Power Transistor (Speaker: Wenwei Xu) 5 Applications of Transistor (Speaker: Wenwei Xu)

22 Field-Effect Transistors
Very little current flows through input (gate) terminals Basics Conduction of a “channel” is controlled by electric field effect Three terminals: gate, source, drain Voltage-controlled current device control terminal current channel of charge carriers for charge carriers control voltage

23 Field-Effect Transistors
A current-controlled current device Comparison BJT FET Input current controls output current Input voltage controls Base Gate Collector Drain Emitter Source BJT vs. FET What was BJT then?

24 Field-Effect Transistors
JFET (Junction FET) MOSFET (Metal-oxide-semiconductor FET) Types JFET (Junction FET) MOSFET (Metal-oxide-semiconductor FET) MESFET (Metal-semiconductor FET) HFET (Hetero-structure FET) MODFET (Modulation doped FET) IGBT (Insulated-gate bipolar transistor) Power MOSFETs FREDFET (Fast reverse or fast recovery epitaxial diode FET) ISFET (Ion-sensitive FET) DNAFET

25 JFETs JFETs General Properties n-channel
Advantages: Much higher input resistance, lower noise, easier fabrication, ability to handle higher currents and powers Disadvantages: Slower speeds in switching circuits, smaller bandwidth for a given gain in an amplifier p-channel

26 n-channel JFET Characteristics

27 n-channel JFET Characteristics Idealized Static

28 n-channel JFET Characteristics Practical Static Transfer

29 MOSFETs MOSFETs or Insulated-gate FET (IGFET) General Properties
n-channel Enhancement General Properties Input resistance even higher Used primarily in digital electronic circuits Provide controlled-source characteristics in amplifier circuits n-channel Depletion

30 n-channel Enhancement MOSFET
Characteristics

31 n-channel Enhancement MOSFET
Characteristics Practical

32 n-channel Depletion MOSFET
Characteristics Practical

33 You CAN do it!! Applications Amplifiers, Switches
Task: Design a n-channel common-source JFET Amplifier You CAN do it!! Psst! You can read it!!

34 “Transistor” Part 4 Introduction to Transistor
1 Introduction to Transistor (Speaker: Sung-bum Kang) 2 Bipolar Junction Transistor (Speaker: Keun Jae Kim) 3 Field Effect Transistor (Speaker: Hongchul Sohn) 4 Power Transistor (Speaker: Wenwei Xu) 5 Applications of Transistor (Speaker: Wenwei Xu)

35 Power Transistor Concerned with delivering high power
Used in high voltage and high current application In general Fabrication process different in order to: Dissipate more heat Avoid breakdown Lower gain than signal level transistor Power transistor is only high power version of signal level transistor. High power mean high current or high voltage. Because of the high power requirement, the fabrication process…

36 Power BJT Same structure to the signal level BJT
The active area is distinctively higher-high current capacity Thick and low-doped collector region Large heat dissipation--- larger dimensions From the sketch here, we can see the power BJT is basically the same to it’s signal level counterpart in structure, the only different is high power. The active area is much higher than…, which makes it able to carry high current. Also, the collector region is low-doped Usually, the dimensions are larger to dissipate more heat.

37 Power MOSFET Same working principles to MOSFET
Designed to handle large power Low internal voltage drop and high current capacity High commutation speed and good efficiency at low voltages—high speed switch The same structure to normal MOSFET That make it a good candidate for high speed switch.

38 wireless communication
Applications of Transistor building blocks for modern electronics Digital logic circuits Microprocessors, microcontrollers, chips (TTL) Photo-transistors Replaces normal switches, mechanical relays. A/D converter Encoders Multiplexers Power supplies Just a general idea about the application of transistor But there are much more than these. wireless communication headphone, microphone microprocessor motor more…

39 Applications(cont.) Transistor Amplifier Switch applications
– Switch for a digital signal: BJT or MOSFET – Switch for a analog signal: JFET – Switch for a power signal: Power MOSFET or BJT – Current controlled-current amplifier: BJT – Voltage controlled-current amplifier: JFET or MOSFET Reasons for the applications

40 BJT as switches Small input voltage and large output current
operated in the cut-off region(open) and saturation region(close) Example: 2N3904 NPN Assuming LED requires mA to provide a bright display and has 2 voltage drop when forwarded biased Output=0V—off Output=5V---on, the transistor is in saturation, with base current The collector current is about 20 manifolds higher than the base current. Collector current (LED current) is limited by collector resistor

41 BJT as amplifiers Low input impedance and high voltage gain
Audio amplifiers, radio frequency amplifiers, regulated power supplies Example Speaker amplifier BJT series produce higher gain

42 Applications of FET Advantages of FET over BJT
They are devices controlled by voltage with a very high input impedance (107 to 1012 ohms) FETs generate a lower noise level than the Bipolar Junction Transistor (BJT) FETs are more stable than BJT with temperature FETs are easier to manufacture than the BJT, because they require fewer steps to be built and they allow more integrated devices in the same IC FETs behave like resistors controlled by voltage for small drain-source voltage values The high input impedance of FET allows them to withhold loads long enough to allow its usage as storage elements Power FETs can dissipate higher power and can switch very large currents. FET holds some advantages over BJT, which make them favorable for some applications.

43 FET Applications of FET Amplifiers Small Signal Low Distortion
High Gain Low Noise amplifier Selectivity High-Frequency Switches Chopper-Type Analog Gate Communicator FET Current Limiters Resistors Mixers Oscillators Protection Diodes Low-leakage

44 FET as analog switch-example
When VGS = 0, FET becomes saturated and it behaves like a small resistance(<100 ohm) and, therefore, VOUT = {RDS/ (RD + RDS (ON))}* Vin RD>>RDS, VOUT → 0 When a negative voltage equal to VGS (OFF) is applied to the gate, the FET operates in the cut-off region and it acts like a very high resistance usually of some mega ohms. Hence output voltage becomes nearly equal to input voltage.

45 Contact information (in order of presenting) Sung-bum Kang Keun Jae Kim Hongchul Sohn Wenwei Xu

46 References www.wikipedia.org www.google.com
“Introduction to Electrical Engineering”, Mulukata S. Sarma, Oxford University Press, 2001, Chap. 7.4~8.4. Fall 2008 Transistors Slides

47 Thank you! Questions?


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