DOCSLIB.ORG

Transistor Biasing

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Transistor Biasing Module 2:BJT Biasing Quote of the day "Peace cannot be kept by force. It can only be achieved by understanding”. ― Albert Einstein DC Load line and Bias Point • DC Load Line – For a transistor a straight line drawn on transistor output characteristics. IC – For CE circuit, the load line is a graph of collector current I versus V for a fixed C CE IB + value of R and supply voltage V C CC + VCE – Load Line? VCC VCE I C RC VBE - - V V I R – From Figure VCE=? CE CC C C – If VBE =0 then IC=0, VCE = VCC plot this point on characteristics(A). – Now assume that ICRC = VCC, i.e. IC = VCC /RC then VCE =0. Plot this point on characteristics(B). – Join points A and B by a straight line. DC Load line contd.. VCE VCC I C RC VV IC CC CE IC RC V CC B IC(sat) RC DC load line VVCE(off ) CC V A CE Example 1. Plot the dc load line for the circuit shown in Fig. Then, find the values of VCE for IC = 1, 2, 5 mA respectively. VVIRCE CC C C VCE 10 for I c 0 10 I 10mA c 110 3 IC (mA) VCE (V) 1 9 2 8 5 5 4 Example 2. For the circuit shown and Plot of the dc load line in Fig. find the values of IC for VCE = 0V and VCE for IC = 0. VVIRCE CC C C 5 I C 4.54mA V CC15V For the previous circuit shown observe the Plot of the dc load line with Rc=4.8 K find the values of IC for VCE = 0V and VCE for IC = 0. I C 3.125mA V CC15V DC Bias Point • DC Bias point or Q point – Identifies the transistor current IC and voltage VCE when no input is applied to the base terminal of the transistor. ~Vi – When an ac signal is applied to the transistor base, IB varies according to the instantaneous =+20 amplitude of signal. This causes IC to vary and consequently produces a variation in VCE. – Now consider the circuit . IC=1mA – Assume the Bias conditions shown in fig. i.e. values of IB,IC & VCE. IB=20A + – What is RC=? VCE + - 10V – The 10 K load line drawn for this circuit is VBE - shown in the next slide. Fig. DC Load line for transistor with a bias point at VCE=10V and IC =1mA. The transistor may be biased to any point on the DC Load Line. IC(mA) IB=40A 2.0 1.95 mA IB=30A 1.6 IB=+20A Q- Point 1.2 IB=20A 0.8 IB=10A IB=-20A 0.4 I =0 V 0.05 mA B CE 0 0 4 8 12 16 20 VCE=-9.5V VCE=+9.5V 19.5V 0.5V Selection of Q point • Note the collector current swings do not exceed the limits of operation(saturation and cutoff). However, as you might already know, applying too much ac voltage to the base would result in driving the collector current into saturation or cutoff resulting in a distorted or clipped waveform. Selection of Q point Optimum Q-point with amplifier operation. IC IC(sat) IB = 50 A IB IICB β IB = 40 A Q-Point IC(sat)/2 IB = 30 A IB = 20 A IB = 10 A IB = 0 A VCE VCC/2 VCC VVIRCE CC C C 11 Effect of Emitter resistance RE • Consider this Fig. • In this case RE is the DC load and the output equation will be VCC VCE IE RE • Now consider the below fig. • Collector and emitter resistors are both present , and total dc load in series with transistor is(RC + RE) VCC VCE I C RC I E RE IC IE VCC VCE IC RC RE Assignment questions 1) Problem 4.6 & 4.7 from David Bell exercise. 2) Draw the common emitter circuit and sketch the input and output characteristics. Also explain active region, cutoff region and saturation region by indicating them on the characteristic curve. 3) Draw the common base circuit and sketch the input and output characteristics. Also explain active region, cutoff region and saturation region by indicating them on the characteristic curve. 4) Determine the operating point for a silicon transistor biased by base bias method with β = 100, RB = 500KΩ RC = 2.5KΩ and VCC = 20V. Also draw the DC load line. Base Bias Method • Circuit operation & Analysis – The circuit arrangement shown in Fig is known as base bias and also as fixed IC current bias. – The Base current is constant and IB + determined by VCC and RB. V – From fig voltage drop across R is + CE B VBE - - VB =IBRB also VB = (VCC-VBE ) since VCC = VB +VBE . – Therefore the base current IB is VCC VBE I B I CQ hFE I B RB – You know that IC is I C I B can be replaced by hFE Base Bias Method contd.. V V I R This collector current can be used with CC CE C C V V I R to calculate VCE. CEQ CC CQ C • Effect of hFE(max) and hFE(min) – Practically the precise current is normally not known. – The transistor is usually identified by its type, number and maximum and minimum values of current gain that can be obtained from manufacturer’s data sheet. – In circuit analysis it is convenient to use a typical value of hFE. Which value of hFE do I use? Transistor specification sheet may list any combination of the following hFE: max. hFE, min. hFE, or typ. hFE. Use typical value if there is one. Otherwise, use hFE(ave) h FE (min) h FE (max) Consider the next example to observe the effect of maximum and minimum value of hFE 16 Example 1. The base bias circuit shown in Fig has RB =470K, RC=2.2K 1)Determine the values of VCE ,IC andIB for hFE=100. 2Calculate the maximum and minimum levels of VCE, IC when hFE(max) =50 and hFE(min) = 200. Plot load line =+18V VCC VBE 18 0.7 I B I B I B 36.8A RB 470 I C I 3.68mA IC hFE IB IC 10036.8A C 3 3 VCE VCC IC RC VCE 18 3.6810 2.210 IB + V + CE VBE - - VCE 9.9V 17 Example 1 contd. • For hFE(min) = 50: I 1.84mA IC 5036.8A C 3 3 VCE 18 1.8410 2.210 VCE 13.95V • For hFE(max) = 200: I 7.36mA IC 20036.8A C 3 3 VCE 18 7.3610 2.210 VCE 1.8V IC hFE IB • Plot the DC load line and mark Q point for three V V I R values of hCEFE. CC C C • Because of this uncertainty of Q point this method is rarely used. Fig. DC Load line for transistor with different hFE plotted for Example 1 IC(mA) 10 Q- Point for hFE=200 8 7.36 mA 6 Q- Point for hFE=100 3.68 mA4 Q- Point for hFE=50 1.84 mA2 VCE 0 0 2 4 6 8 10 12 14 16 18 13.95V 1.8V 9.9V Example 2. Determine the operating point for a silicon transistor biased by base bias method with β = 100, RB = 500KΩ RC = 2.5KΩ and VCC = 20V. Also draw the DC load line. =+20V 20 0.7 I B 3 I B 38.6A VCC VBE 50010 I B RB I C I 3.86mA IC hFE IB IC 10038.6A C 3 3 VCE VCC IC RC VCE 20 3.8610 2.510 IB + VCE + VBE - - VCE 10.35V 20 Example 2. V 20 I CC 8mA IC c(sat) 3 Rc 2.510 VCC I c(sat) 8mA IC(sat) RC Q- Point 3.86mA VVCE(off ) CC = 20V VCE 10.35V Base bias characteristics. Circuit recognition: A single resistor (RB) between the base terminal and VCC. No emitter resistor. Advantage: Circuit simplicity. Disadvantage: Q-point shift with temp. Applications: Switching circuits only. 22 Base bias characteristics. (2) Load line equations: VCC I c(sat) Rc VCE(OFF ) VCC Q-point equations: VCC VBE I B RB I CQ hFE I B VCEQ VCC I CQ RC 23 Design of Base bias circuit To design the circuit means to compute the values of resistors RB and RC for the required specifications i.e. (ICQ,VCEQ and available hFE) Design equations: I CQ hFE I B VCC VBE RB I B VCC VCEQ RC I CQ 24 Example 3. Design a base bias circuit as in fig below to have β = 100, VCE = 7 V, IC = 5mA and VCC = 20V. 3 I C 510 =+20V I B I B I B 50A hFE 100 V V 20 0.7 IC CC BE RB RB 6 I B 5010 RB 386K IB + VCE Use 390KΩ standard value + VBE - - VCC VCE 20 7 RC RC 3 I C 510 RC 2.6K Use 2.2K standard value 25 Voltage Divider method • Voltage-divider bias is the most widely used type of bias circuit. Only one power supply is needed and voltage-divider bias is more + + V stable(less variation with ) + + CE - V - than other bias types. For BE + VC this reason it will be the VB primary focus for study. VE - - - Voltage Divider method • It is seen from the fig that along with the resistor RC there is an emitter resistor RE connected in series with transistor. • Therefore the total load in series with transistor is(RC + RE), and this must be used when drawing the DC load line.
Load more

Recommended publications
  • Shults Robert D 196308 Ms 10
    AN INVESTIGATION OF THE INFLUENCE OF CIRCUIT PARAMETERS ON THE OUTPUT WAVESHAPE OF A TUNNEL DIODE OSCILLATOR A THESIS Presented to The Faculty of the Graduate Division by Robert David Shults In Partial Fulfillment of the Requirements for the Degree Master of Science in Electrical Engineering Georgia Institute of Technology June, I963 AN INVESTIGATION OF THE INFLUENCE OF CIRCUIT PARAMETERS ON THE OUTPUT WAVESHAPE OF A TUNNEL DIODE OSCILLATOR Approved: —VY -w/T //'- Dr. W. B.l/Jonesj UJr. (Chairman) _A a t~l — Dry 3* L. Hammond, Jr. V ^^ __—^ '-" ^^ *• Br> J. T. Wang * Date Approved by Chairman: //l&U (A* l/j^Z) In presenting the dissertation as a partial, fulfillment of the requirements for an advanced degree from the Georgia Institute of Technology, I agree that the Library of the Institution shall make it available for inspection and circulation in accordance witn its regulations governing materials of this type. I agree -chat permission to copy from, or to publish from, this dissertation may be granted by the professor under whose direction it was written^ or, in his absence, by the dean of the Graduate Division when luch copying or publication is solely for scholarly purposes ftad does not involve potential financial gain. It is under­ stood that any copying from, or publication of, this disser­ tation which involves potential financial gain will not be allowed without written permission. _/2^ d- ii ACKNOWLEDGMEBTTS The author wishes to thank his thesis advisor, Dr. W. B„ Jones, Jr., for his suggestion of the problem and for his continued guidance and encouragement during the course of the investigation.
    [Show full text]
  • Transistor Circuits
    Transistor Circuits Learning Outcomes This chapter deals with a variety of circuits involving semiconductor devices. These will include bias and stabilisation for transistors, and small-signal a.c. amplifi er circuits using both BJTs and FETs. The use of both of these devices as an electronic switch is also considered. On completion of this chapter you should be able to: 1 Understand the need for correct biasing for a transistor, and perform calculations to obtain suitable circuit components to achieve this effect. 2 Understand the operation of small-signal amplifi ers and carry out calculations to select suitable circuit components, and to predict the amplifi er gain fi gure(s). 3 Understand how a transistor may be used as an electronic switch, and carry out simple calculations for this type of circuit. 1 Transistor Bias In order to use a transistor as an amplifying element it needs to be biased correctly. Although d.c. signals may be amplifi ed, the amplifi cation of a.c. signals is more common. However, the bias is provided by d.c. conditions. Consider a common emitter connected BJT and its input characteristic as illustrated in Fig. 1 . The inclusion of resistor RC is not required at this stage, but would be present in any practical amplifi er circuit, so is shown merely for completeness. This resistor is called the collector load resistor. With the switch in position ‘ 1 ’ the value of forward bias V BEQ has been chosen such that it coincides with the centre of the linear portion of the input characteristic. This point on the characteristic is identifi ed by the letter Q, because, without any a.c.
    [Show full text]
  • Amplifier En.Pdf
    Bipolar Junction Transistor Amplifiers Semiconductor Elements 1 © 2010,EE141 Доц.д-р. T.Василева What is an Amplifier? An amplifier is a circuit that can increase the peak-to-peak voltage, current, or power of a signal. It allows a small signal to control a much larger, high-powered one. Definitions of voltage, current and power gain coefficients are also given in figure. Lowercase italic letters indicate ac voltage and alternating currents. 2 © 2010,EE141 Доц.д-р. T.Василева 1 Amplifier Configurations There are three configurations of a BJT amplifier circuit: common- emitter (CE), common-collector (CC) and common-base (CB). The configuration is named for the electrode that is common for input and output networks. The CE is the most widely used for amplifiers because it has the best combination of current gain and voltage gain. In CE the input and output voltage are 180° out of phase, called an inversion. 3 © 2010,EE141 Доц.д-р. T.Василева Transistor Biasing Circuit with fixed base current For the transistor to operate properly as an amplifier, the base-emitter junction should be forward-biased and the base-collector junction – reverse-biased. This is called forward-reverse bias. The three dc voltages for the biased transistor are the emitter voltage UE, the collector voltage UC and the base voltage UB. These voltages are measured with respect to ground. 4 © 2010,EE141 Доц.д-р. T.Василева 2 Voltage-Divider Biasing (VDB) Voltage divider Circuit with fixed base voltage. Iдел >> IB The voltage-divider bias (VDB) configuration uses only a single dc source to provide forward-reverse bias to the transistor.
    [Show full text]
  • The Venerable Triode
    The Venerable Triode The very first gain device, the vacuum tube Triode, is still made after more than a hundred years, and while it has been largely replaced by other tubes and the many transistor types, it still remains popular in special industry and audio applications. I have some thoughts on why the Triode remains special for audio amplifiers (apart from sentimental value) that I would like to share. But first, a quick tutorial about Triodes: The earliest Triode was Lee De Forest's 1906 “Audion”. Over a hundred years development has resulted in many Triodes, large and small. The basic design has remained much the same. An evacuated container, usually glass, holds three signal connections, seen in the drawing as the Cathode, Grid and Plate (the Plate is also referred to as the Anode). In addition you see an internal heater, similar to a light bulb filament, which is used to heat the Cathode. Triode operation is simple. Electrons have what's known as “negative electrostatic charge”, and it is understood that “like” charges physically repel each other while opposite charges attract. The Plate is positively charged relative to the Cathode by a battery or other voltage source, and the electrons in the Cathode are attracted to the Plate, but are prevented by a natural tendency to hang out inside the Cathode and avoid the vacuum. This is where the heater comes in. When you make the Cathode very hot, these electrons start jumping around, and many of them have enough energy to leave the surface of the Cathode.
    [Show full text]
  • Lab 5 Assignment
    EE 462: Laboratory Assignment 5 Biasing N- channel MOSFET Transistor by Dr. A.V. Radun and Dr. K.D. Donohue (2/21/07) Updated Spring 2008 by Stephen Maloney Department of Electrical and Computer Engineering University of Kentucky Lexington, KY 40506 I. Instructional Objectives • Analyze the metal oxide semiconductor (MOS) field effect transistor (FET) (MOSFET) using a DC load line • Design a circuit to set a DC operating point for a MOSFET • Measure the operating points in a DC biased FET circuit • Become more familiar with programming in LabVIEW (See Horenstein 5.2, 7.3.1, and 7.3.3) II. Background Transistors are nonlinear devices; however, over certain operating regions they can be approximated with linear models. To ensure a transistor operates in its linear region, a DC level is added to its input signal. The design of this DC level is referred to as biasing the transistor. The DC current and voltage values are referred to as the transistor’s DC operating point (or its bias point) (or its quiescent point). Once a transistor is biased in a linear region, small changes for the input currents and voltages around the bias point will cause the outputs to change in a linearly proportional manner (approximately). It is assumed that the variation of the transistor's currents and voltages are small enough such that they do not move the system into nonlinear operation regions (triode region or cutoff). The simplest common source MOSFET amplifier biasing scheme is shown in Fig. 1. Since only the DC operating point is of interest right now, the time varying part of the input signal is omitted.
    [Show full text]
  • Diodes Lesson #6 Chapter 3
    Diodes Lesson #6 Chapter 3 BME 372 Electronics I – 180 J.Schesser Diodes • Typical Diode VI Characteristics – Forward Bias Region i – Reverse Bias Region d – Reverse Breakdown Region + - vd – Forward bias Threshold 5 i d 4 3 2 1 v d 0 -7-5-3-11357 -1 Reverse -2 breakdown Reverse bias Forward bias region -3 region region -4 -5 VI stands for Voltage Current BME 372 Electronics I – 181 J.Schesser Zener Diodes • Operated in the breakdown region. • Used for maintain a constant output voltage BME 372 Electronics I – 182 J.Schesser Load Line Analysis • Let’s see how to use a diode in a circuit. R Load Line 39 i D amps 35 + + 31 iD 27 VSS vD 23 -- -- 19 15 11 7 3 • Use KVL for this circuit -1 -0. -0. -0. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 3 2 1 v D volts Vss = RiD + vD • This equation is plotted on the same graph as the diode VI characteristics. BME 372 Electronics I – 183 J.Schesser Load Line Analysis i D amps Vss = RiD + vD 39 Operating Point Vss =1.6V, R=50kΩ 35 Q-point vD=0; 31 27 Load Line iD= Vss / R 23 Highest Voltage =32amps 19 vD=Vss Highest Current 15 =1.6V; 11 7 iD=0 3 -1 -0. -0. -0. 0 0.10.20.30.40.50.60.70.80.91 1.11.21.31.41.51.61.71.8 3 2 1 BME 372 Electronics I – 184 J.Schesserv D volts Ideal Diode • Basically, a switch – Forward Bias: any current allowed, diode on – Reverse Bias: zero current, diode off 5 – No reverse breakdown region i d 4 3 2 Diode on Diode off 1 v d 0 -7-5-3-11357 -1 -2 -3 -4 -5 BME 372 Electronics I – 185 J.Schesser How do we Analysis a Circuit with an Ideal Diode • For a real diode we use load line (graphical analysis) • For an ideal diode, we use a deductive method: 1.
    [Show full text]
  • Transistor Biasing
    Transistor Biasing Transistor Biasing is the process of setting a transistors DC operating voltage or current conditions to the correct level so that any AC input signal can be amplified correctly by the transistor Transistor Biasing- S.Gayathri Priya 1 Need for Biasing A transistors steady state of operation depends a great deal on its base current, collector voltage, and collector current and therefore, if a transistor is to operate as a linear amplifier, it must be properly biased to have a suitable operating point. Establishing the correct operating point requires the proper selection of bias resistors and load resistors to provide the appropriate input current and collector voltage conditions. Transistor Biasing- S.Gayathri Priya 2 Q Point The correct biasing point for a bipolar transistor, either NPN or PNP, generally lies somewhere between the two extremes of operation with respect to it being either “fully-ON” or “fully- OFF” along its load line. This central operating point is called the “Quiescent Operating Point”, or Q-point for short. Transistor Biasing- S.Gayathri Priya 3 BJT Biasing methods The various types of biasing methods are: • Fixed Bias • Collector to base bias • Voltage divider bias Transistor Biasing- S.Gayathri Priya 4 Fixed Bias The transistors base current, IB remains constant for given values of Vcc, and therefore the transistors operating point must also remain fixed.Hence referred as fixed biasing Transistor Biasing- S.Gayathri Priya 5 Fixed Bias This two resistor biasing This type of transistor network is used to establish biasing arrangement is also the initial operating region of beta dependent biasing as the transistor using a fixed the steady-state condition of current bias.
    [Show full text]
  • Tunnel-Diode Microwave Amplifiers
    Tunnel diodes provide a means of low-noise microwave amplification, with the amplifiers using the negative resistance of the tunnel diode to a.chieve amplification by reflection. Th e tunnel diode and its assumed equivalent circuit are discussed. The concept of negative-resistance reflection amplifiers is discussed from the standpoints of stability, gain, and noise performance. Two amplifi,er configurations are shown. of which the circulator-coupled type 1'S carried further into a design fo/' a C-band amplifier. The result 1'S an amph'fier at 6000 mc/s with a 5.S-db noise figure over 380 mc/s. An X-band amplifier is also reported. C. T. Munsterman Tunnel-Diode Microwave Am.plifiers ecent advances in tunnel-diode fabrication where the gain of the ith stage is denoted by G i techniques have made the tunnel diode a and its noise figure by F i. This equation shows that Rpractical, low-noise, microwave amplifier. Small stages without gain (G < 1) contribute greatly to size, low power requirements, and reliability make the overall system noise figure, especially if they these devices attractive for missile application, es­ are not preceded by some source of gain. If a pecially since receiver sensitivity is significantly low-noise-amplification device can be located near improved, with resulting increased homing time. the source of the signal, the contribution from the Work undertaken at APL over the past year has successive stages can be minimized by making G] resulted in the unique design techniques and hard­ sufficiently large, and the overall noise figure is ware discussed in this paper.-Y.· then that of the amplifier Fl.
    [Show full text]
  • Electronic Circuits Lectures
    UCRL 37 fAt,1/A , ~ IiI, :l~ fJI- 3 UNIVERSITY OF CALIFORNIA TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Dioision, Ext. 5545 c' (', ft) BERKELEY. CALIFORNIA r ~ ~' ()) \~ ----j\ '1 I J Lawrence Radiation Laboratory Library University of California, Berkeley UNIVERSITY OF CALIFORNIA (~\ RAD IATI ON I,ABOR}\TORY J Lee-fvye s Cover Sheet INDEX NO. U d L ~:; 7 If /. ~ ~ 3 ' Do not remove This document contains pages I ! and_Plate~f figures. J1 This is copy .0£_. Series-A;C- .. Issued to :..............._-..,..._....--,..__.. _ Each person who received this document m1,lstsign the cover sheet in the space below. ---._~--_...-.-. Route to Noted by Route to Noted by Date =-:;::,..··.=="::;===:e:::·.""'T"'"=====::::;===F~';,,,:;- _-~_:;;;::£.l.- ~_rr-:=~4=U:t-', ~t~ -~ -: w:-+'._ ....:=-~ _. Ii. -===== .,~~+.- .. -----_....-+---.......,.........---+-- , ....ij--- _. ........-.__..... ) ._---..-1--..,....,.-._.··n·, - .. --.,...-.-+.......-----+------ 1 '--.._-...........-..........._--,;,..-.-- ----.......--f.-------~-_.- __H_......__...- .....--.,....,~--I-- .........,....._--,+- _ ------+---..........---01----..----14--.--,--....-...:--.......-......--~.,.-...--+ ...----.... ._-!-----_ .."'"'"'...._-- -.----+--....----+------tt- --------I-_----~-.-. -_1+........---....,..,..,·-r-!I-----.....-_+--·---- j I i I ---..--.-.-4-·----·-J..-~----·!+1 .--.-...............-.-~---+.......---~ ...........-+---- l ~ ........._ ............,... .l..-I.,......
    [Show full text]
  • Lecture #3 BJT Biasing Circuits Instructor
    Banna Benha University - Faculty of Engineering at Shoubra © Ahmad El ECE-312 Electronic Circuits (A) Lecture #3 BJT Biasing Circuits Instructor: Dr. Ahmad El-Banna October 2014 Banna Agenda - Operating Point © Ahmad El Transistor DC Bias Configurations Design Operations Various BJT Circuits 312 2014 Lec#3 , Oct , Troubleshooting Techniques & Bias Stabilization - ECE Practical Applications 2 Banna Introduction - • Any increase in ac voltage, current, or power is the result of a transfer of energy from the applied dc supplies. © Ahmad El • The analysis or design of any electronic amplifier therefore has two components: a dc and an ac portion. • Basic Relationships/formulas for a transistor: 312 2014 Lec#3 , Oct , - • Biasing means applying of dc voltages to establish a fixed level of ECE current and voltage. >>> Q-Point 3 Banna Operating Point - • For transistor amplifiers the resulting dc current and voltage establish an operating point on the characteristics that define the © Ahmad El region that will be employed for amplification of the applied signal. • Because the operating point is a fixed point on the characteristics, it is also called the quiescent point (abbreviated Q-point). Transistor Regions Operation: 1. Linear-region operation: Base–emitter junction forward-biased Base–collector junction reverse-biased 312 2014 Lec#3 , Oct , 2. Cutoff-region operation: - Base–emitter junction reverse-biased Base–collector junction reverse-biased ECE 3.Saturation-region operation: Base–emitter junction forward-biased 4 Base–collector junction forward-biased Banna - © Ahmad El • Fixed-Bias Configuration • Emitter-Bias Configuration • Voltage-Divider Bias Configuration • Collector Feedback Configuration • Emitter-Follower Configuration 312 2014 Lec#3 , Oct , • Common-Base Configuration - • Miscellaneous Bias Configurations ECE TRANSISTOR DC BIAS CONFIGURATIONS 5 Banna Fixed-Bias Configuration - • • Fixed-bias circuit.
    [Show full text]
  • Field Effect Transistors
    Field Effect Transistors Lecture 9 Types of FET • Metal Oxide Semiconductor Field Effect Transistor – MOSFET – Enhancement mode – Depletion mode • Junction FETs • p channel vs n channel 38 Metal Oxide Semiconductor Field Effect Transistor MOSFET (NMOS) Enhancement Mode • Consists of Four terminals – Drain which is n-doped material G S D – Source also n-doped material Oxide – Base which is p-doped material Metal Gate Drain – Gate is a metal and is insulated from the Drain, Source Source and Base by a thin layer of silicon dioxide ~ .05-.1mm thick • Basically, an electric current flowing from drain to source, iD, is controlled by the amount of voltage n+ n+ (electric field) appearing between the gate and base p (note that the base and source are usually tied together and therefore, it is referred to as the gate to source voltage or gate voltage), vGS. Substrate, body or Base • iD flows through a channel of n-type material which B is induced by vGS. The amount of iD is a function of the thickness of the channel and the voltage between drain and source, vDS • However, the thickness of channel is controlled by the level of gate voltage. (The width, .5 to 500 mm, and length, .2 to 10 mm, of the channel is shown in the diagram.) 39 Metal Oxide Semiconductor Field Effect Transistor MOSFET (NMOS) Enhancement Mode • Consists of Four terminals – Drain which is n-doped material – Source also n-doped material G – Base which is p-doped material S D – Gate is a metal and is insulated from the Drain, Oxide Source and Base by a thin layer of silicon Metal Gate Drain dioxide ~ .05-.1mm thick Source • Basically, an electric current flowing from drain to source, iD, is controlled by the amount of voltage (electric field) appearing between the gate and base W (note that the base and source are usually tied n+ L n+ together and therefore, it is referred to as the gate to p source voltage or gate voltage), vGS.
    [Show full text]
  • Chapter 5 BJT Biasing Circuits
    Chapter 5 BJT Biasing Circuits 5.1 The DC Operation Point [5] DC Bias: Bias establishes the dc operating point for proper linear operation of an amplifier. If an amplifier is not biased with correct dc voltages on the input and output, it can go into saturation or cutoff when an input signal is applied. Figure 5.1 shows the effects of proper and improper dc biasing of an invert amplifier. Figure 5.1 Examples of linear and nonlinear operation of an inverting amplifier (the triangle symbol). [5] 177 | P a g e In part (a), the output signal is an amplified replica of the input signal except that it is inverted, which means that it is 180 out of the phase with the input. Part (b) illustrates limiting of the positive portion of the output voltage for a result of a dc operating point (Q-point) being too close to cutoff. Part (c) shows limiting of the negative portion of the output voltage as a result of a dc operating point being too close to saturation. Linear Operation: The region along the load line including all points between saturation and cutoff is generally known as the linear region of the transistor’s operation. The output voltage in this region is ideally a linear reproduction of the input. Figure 5.2 shows an example of the linear operation of a transistor. AC quantities are indicated by lower case italic subscripts. Figure 5.2 Variations in collector current and collector-to-emitter voltage as a result of a variation in base current.
    [Show full text]