ANALOG ELECTRONICS (AE)

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1 ANALOG ELECTRONICS (AE) ABOUT COURSE& MARKS SCHEME: 1 Prepared by: BE-EC Amish J. Tankariya SEMESTER-III SUBJECT- ANALOG ELECTRONICS (AE) GTU Subject Code : SYLLABUS: 3 4 1

REFERENCE BOOKS: ACTIVE LEARNING ASSIGNMENTS: Preparation of power-point slides, which include videos, animations, pictures, graphics for better understanding theory and practical work The faculty

2 REFERENCE BOOKS: ACTIVE LEARNING ASSIGNMENTS: Preparation of power-point slides, which include videos, animations, pictures, graphics for better understanding theory and practical work The faculty will allocate chapters/ parts of chapters to groups of students so that the entire syllabus to be covered. The power-point slides should be put up on the web-site of the College/ Institute, along with the names of the students of the group, the name of the faculty, Department and College on the first slide. 5 ThebestthreeworksshouldsubmittoGTU. 6 ATOMS IN SOLIDS Atoms form a lattice structure MODULE: 1 7 Diodes The lattice affects the structure of the energy levels of each atom. 8 2

BAND THEORY LATTICE BANDS Threebandsofenergylevelsform Valence Band most of the electrons are here Conduction Band electrons here give the material electrical conductivity Forbidden Band electrons

3 BAND THEORY LATTICE BANDS Threebandsofenergylevelsform Valence Band most of the electrons are here Conduction Band electrons here give the material electrical conductivity Forbidden Band electrons must jump this bandtogetfromthevalencetotheconduction band 9 10 CONDUCTION RESISTIVITY Inorderforanelectrontobecomefreeand participate in current flow, it must gain enough energy to jump over the forbidden band For semiconductors at room temperature, there is not enough energy to conduct. As temperature increases more electrons have the energy to jump the forbidden band R Semiconductor T Conductor Resistivity decreases This is the opposite behavior of conductors

SEMICONDUCTORS When an electron becomes free, it creates a hole in the lattice structure ELECTRON AND HOLE MOVEMENT 13 14 A hole is effectively a positive charge INTRINSIC SEMICONDUCTOR

, GaAs) EXTRINSIC SEMICONDUCTORS A pure semiconductors where a small amount of another element is added to replace atoms in the lattice (doping).

4 SEMICONDUCTORS When an electron becomes free, it creates a hole in the lattice structure ELECTRON AND HOLE MOVEMENT A hole is effectively a positive charge INTRINSIC SEMICONDUCTOR Elemental or pure semiconductors have equal numbers of holes and electrons Depends on temperature, type, and size. Compound Semiconductors can be formed from two (or more) elements(e.g., GaAs) EXTRINSIC SEMICONDUCTORS A pure semiconductors where a small amount of another element is added to replace atoms in the lattice (doping). The aim is to produce an excess of either electrons (n-type) or holes (p-type) Typical doping concentrations are one part in ten million Doping must be uniform throughout the lattice so that charges do not accumulate

P-TYPE p-type: Aluminum, indium, gallium, boron A silicon crystal doped with a trivalent impurity.

17 N-TYPE n-type: Arsenic, antimony, bismuth, phosphorus A silicon crystal doped by a pentavalent element.

18 INADCCIRCUIT P-N JUNCTION DIODE On its own a p-type or n-type semiconductor is not very useful.

5 P-TYPE p-type: Aluminum, indium, gallium, boron A silicon crystal doped with a trivalent impurity. Each dopant atom gives rise to a hole, and the semiconductor becomes p type. 17 N-TYPE n-type: Arsenic, antimony, bismuth, phosphorus A silicon crystal doped by a pentavalent element. Each dopant atom donates a free electron and is thus called a donor. The doped semiconductor becomes n type. 18 INADCCIRCUIT P-N JUNCTION DIODE On its own a p-type or n-type semiconductor is not very useful. However when combined very useful devices can be made. The p-n junction can be formed by allowing a p- type material to diffuse into a n-type region at high temperatures. Thep-njunctionhasledtomanyinventionslike the diode, transistors and integrated circuits. P material (anode) N material (cathode) 5

P-N JUNCTION DIODE Freeelectronsonthen-sideandfreeholesonthep-side can initially diffuse across the junction. Uncovered charges are left in the neighbourhood of the junction.

6 P-N JUNCTION DIODE Freeelectronsonthen-sideandfreeholesonthep-side can initially diffuse across the junction. Uncovered charges are left in the neighbourhood of the junction. This region is depleted of mobile carriers and is called the DEPLETION REGION(thickness µm). P-N JUNCTION DIODE The diffusion of electrons and holes stop due to the barrier p.d(p.d across the junction) reaching some critical value. The barrier p.d(or the contact potential) depends on the type of semiconductor, temperature and doping densities. At room temperature, typical values of barrier p.d. are: Ge~ V Si~ V FORWARD BIAS P-N JUNCTION WhenanexternalvoltageisappliedtotheP-Njunction makingthepsidepositivewithrespecttothensidethe diodeissaidtobeforwardbiased(f.b). The barrier p.d. is decreased by the external applied voltage. The depletion band narrows which urges majority carriers to flow across the junction. AF.B.diodehasaverylowresistance. REVERSE BIAS P-N JUNCTION WhenanexternalvoltageisappliedtothePNjunction makingthe Psidenegativewithrespecttothe Nside thediodeissaidtobereversebiased(r.b.). The barrier p.d. increases. The depletion band widens preventing the movement of majority carriers across the junction. AR.B.diodehasaveryhighresistance. 23 6

7 I-V CHARACTERISTICS Only thermally generated minority carriers are urged across the p-n junction. Therefore the magnitude of the reverse saturation current (or reverse leakage current) depends on the temperature of the semiconductor. WhenthePNjunctionisreversedbiasedthewidthofthe depletion layer increases, however if the reverse voltage gets too large a phenomenon known as diode breakdown occurs. 25 DEPLETION REGION I-V CHARACTERISTICS When the diode is F.B., the current increases exponentially with voltage except for a small range close to the origin. WhenthediodeisR.B.,thereversecurrentisconstant and independent of the applied reverse bias. Turn-on or cut-in (threshold) voltage Vγ: for a F.B. diode it is the voltage when the current increases appreciably from zero. Itisroughlyequaltothebarrierp.d.: ForGe,Vγ~ V(atroomtemp.)[standard0.3] ForSi,Vγ~ V(atroomtemp.)[standard0.7] 27 As free electrons and holes diffuse across the junction, a region of fixed ions is left behind. This region is known as the depletion region. 7

8 DIODE APPLICATION: RECTIFICATION Rectification is the process whereby a sinusoidal alternating current is converted into direct current. There are two types of rectification: Half-Wave Rectification Full-Wave Rectification Half-Wave Rectification A single diode can be used to achieve half-wave rectification. Thedisadvantageofthismethodisthatonlyhalf ofthesignalisused.theoutputvoltageisdirect (thereisno changeinpolarity)howeveritisnot very smooth. 30 Full-Wave Rectification During the half-cycle in which A is at the higher potential diodes D2 and D3 conduct. During the subsequent half-cycle diodes D4 and D1 conduct. Note that in both cycles the current flows in the same direction through resistor R

9 The output voltage is smoother than the output for half-wave rectification but still not smooth enough for many applications. SMOOTHING A capacitor can be used to filter (remove the voltage variation) the output voltage. Asthevoltagegrowsthecapacitorchargesup,andasthe voltage falls the capacitor discharges through the resistor. If the capacitance is large enough the voltage will not fallalotbeforethecapacitorischargeduponcemore.in this way the output voltage is smoothened Note that a small ripple is left. This ripple is reduced by increasing the capacitance of the capacitor. It should be noted however that increasing the capacitance increases the current which surges through the diode as the capacitor is charged up once every cycle. This surge could possibly destroy the diode. INTRODUCTION TO TRANSISTORS

10 INTRODUCTION TO TRANSISTORS The BJT Bipolar Junction Transistor Atransistorisusedto control current flow. Itismadeof three layersofsemiconductormaterial Theconstructionis similar to the diode Transistors can often take the place of mechanical switches and relays A transistor can be thought of as two diodes that share a common center layer The emitter heavily doped, Thebase lightlydoped, E npn n p n The Two Types of BJT Transistors: B B C pnp C E p n p B B C C The collector Moderately doped. Theouterlayers(C&E)havewidthsmuchgreaterthan the sandwiched(b) p- or n-type material BJT bipolar junction transistor holes and electrons as charge carrier. only one carrier unipolar device E Collector doping is usually ~ 10 9 Base doping is slightly higher ~ Emitter doping is much higher ~ E ABOUT SYMBOL OF TRANSISTORS The common schematic symbols used for transistors The emitter alwayshasalinewiththearrow The base istheheavylineatthebottomofthe symbol The collector isthelinewithoutthearrow TRANSISTOR CONSTRUCTION Adding a second layer of P-type material to the basic diode construction creates a PNP transistor Adding a second layer of N-type material to the basic diode construction creates a NPN transistor 10

BASIC TRANSISTOR OPERATION Supplying a positive/negative voltage to the base supplies the electrons needed for current flow One p-n junction of a transistor is reverse biased, while the other is

11 BASIC TRANSISTOR OPERATION Supplying a positive/negative voltage to the base supplies the electrons needed for current flow One p-n junction of a transistor is reverse biased, while the other is forward biased. transfer + resistor transistor NPN VSPNP NPNandPNPfunctionthesameway Power supply polarities are reversed ForNPN,positivesupplyisused NPN has higher frequency response as electrons are the charge carriers. NPNismorewidelyused pointing in not pointing in. CE TRANSISTOR OUTPUT CHARACTERISTIC Operation region summary Operation Region IB or VCE Char. BC and BE Junctions Mode Cutoff IB = Very small Reverse & Reverse Open Switch Saturation VCE = Small Forward & Forward Closed Switch Active Linear VCE = Moderate Reverse & Forward Linear Amplifier 43 Break-down VCE = Large Beyond Limits Overload 11

12 TRANSISTOR APPLICATIONS Switch Amplifier Oscillator TRANSISTOR CONFIGURATIONS Common Emitter (CE) Common Base (CB) Common Collector (CC). THREE POSSIBLE CONFIGURATIONS OF BJT Biasing the transistor refers to applying voltages to the transistor to achieve certain operating conditions. 1. Common-Base Configuration (CB) : input = V EB & I E output = V CB & I C 2. Common-Emitter Configuration (CE): input = V BE & I B output= V CE & I C 3. Common-Collector Configuration (CC) :input = V BC & I B (Also known as Emitter follower) output = V EC & I E

GAIN FACTORS COMMON BASE NPN α = β = γ = I I

/I B > 1 Usually given for common collector

13 GAIN FACTORS COMMON BASE NPN α = β = γ = I I I I C E C B I I E B Usually given for common base amplifier α = I C /I E < 1 Usually given for common emitter amplifier β = I C /I B > 1 Usually given for common collector amplifier COMMON EMITTER NPN COMMON COLLECTOR NPN 13

14 BRINGING IT TOGETHER Type Relation between input/output phase Common Base Common Emitter Common Collector Voltage Gain High Medium Low Current Gain Low (α) Medium (β) High (γ) Power Gain Low High Medium BJT TRANSISTOR MODELING The key to transistor small-signal analysis is the use of equivalent circuits(models) A model is the combination of circuit elements, properly chosen, that best approximates the actual behavior of a semiconductor device under specific operating conditions The hybrid-parameter equivalent circuit continues to be very popular for modeling of transistorized circuit. Input Z Low Medium High Output Z High Medium Low 54 TWO-PORT NETWORK Any linear two-port network be characterized by the four variables V 1 ;V 2 ; I 1, and I 2,onlytwoof which can be independent. A transistor can be treated as a two part network. HYBRID-PARAMETER MODEL

VARIOUS 2 PORT PARAMETER MODEL 1) Open Circuit Impedance parameter Z 11, Z 12, Z 21, Z 22 I 1, I 2 Independent V 1,V 2 Dependent 2) Short circuit Admittance parameter Y 11, Y 12, Y 21, Y 22 V 1,V 2

15 VARIOUS 2 PORT PARAMETER MODEL 1) Open Circuit Impedance parameter Z 11, Z 12, Z 21, Z 22 I 1, I 2 Independent V 1,V 2 Dependent 2) Short circuit Admittance parameter Y 11, Y 12, Y 21, Y 22 V 1,V 2 Independent I 1, I 2 Dependent 3) Hybrid Parameters H 11, H 12, H 21, H 22 I 1, V 2 Independent V 1,I 2 Dependent 57 H-PARAMETERS If V 2 and I 1 are taken as the independent variables, a characterization of the two-port network via the hybrid parameters(or, simply, the h-parameters) results: Or The parameters relating the four variables are called h-parameters from the word hybrid. Theterm hybrid hybrid set of units of h-parameters. 58 HYBRID PARAMETERS Two of the h parameters are determined by shortcircuiting port 2, while the remaining two parameters are found by open-circuiting port 1: H- para. significance Condition Name h 11 =h i Input resistance h 12 =h r Voltage feedback ratio h 21 =h f Forward current gain h 22 =ho Output conductance Output shorted Input open Output shorted Input open Short-circuit inputimpedance parameter Open-circuit reverse transfer voltage ratio parameter Short-circuit forward transfer current ratio parameter Open-circuit output Admittance parameter. NOTE: 59 The numerical subscript notation for h parameters (viz. h 11,h 21,h 12 andh 22 )isusedin general circuit analysis. 15

H PARAMETER EQUIVALENT CIRCUIT TRANSISTOR H PARAMETERS NOTATION Convenient alternative natation recommended by IEEE standard are given below. The first letter indicates the nature of parameter.

The output circuit involves two components; a currentgenerator h 21 i 1 and shunt resistance h 22 and is derived from equation(ii).

16 H PARAMETER EQUIVALENT CIRCUIT TRANSISTOR H PARAMETERS NOTATION Convenient alternative natation recommended by IEEE standard are given below. The first letter indicates the nature of parameter. The second letter indicates the circuit arrangement(i.e. CB,CEor CC). The input circuit appears as a resistance h 11 in series withavoltagegenerator h 12 v 2. This circuit is derived from equation(i). The output circuit involves two components; a currentgenerator h 21 i 1 and shunt resistance h 22 and is derived from equation(ii) MEANING OF NUMERIC NOTATION WORTH NOTING POINTS ABOUT THE H PARAMETER EQUIVALENT CIRCUIT The numeric notation shown behind is used in general circuit analysis. The first number designates the circuit in which the effect takes place and The second number designates the circuit from which the effect comes. Forinstance, h 21 is the short-circuit forward current gain or theratioof the currentin the output (circuit 2) to the current in the input (circuit 1) 63 The equivalent circuit is extremely useful for two main reasons. First, it isolates the input and output circuits, their interaction being accounted for by the two controlled sources. Thus, the effect of output upon input is represented by the equivalent voltage generator h 12 v 2 and its value depends upon output voltage. Similarly, the effect of input upon output is represented by current generator h 21 i 1 and its value depends upon input current. Secondly, the two parts of the circuit are in a form whichmakes it simpletotakeintoaccountsourceand load circuits

radio frequencies. Theyareeasytomeasure. It isolates the input and output circuits.

They are convenient to use in circuit analysis and design. Easily convert able from one configuration to other.

17 WHY H PARAMETER?? OR ADVANTAGES Firstly, the values of circuit components are readily available h parameters are real numbers up to radio frequencies. Theyareeasytomeasure. It isolates the input and output circuits. They can be determined from the transistor static characteristics curves. They are convenient to use in circuit analysis and design. Easily convert able from one configuration to other. Readily supplied by manufactories. 65 HYBRID MODEL AND EQUATIONS FOR THE TRANSISTOR IN THREE DIFFERENT CONFIGURATIONS HYBRID CB CIRCUIT 66 Q.1 (a) Determine h-parameter for two port networks. Also draw the hybrid model for CE, CB and CC Configuration.[07]. [GTU-SUMMER 2015] HYBRID CE CIRCUIT HYBRID CC CIRCUIT

ANALYSIS OF A TRANSISTOR AMPLIFIER CIRCUIT USING H PARAMETERS To form a transistor

indicated in Fig. Transistor in any one of the three possible configurations.

THE TRANSISTOR IS REPLACED BY ITS H-PARAMETER MODEL.

output to input currents, THEINPUTIMPEDANCEZI: The resistance Rs, represents the

18 ANALYSIS OF A TRANSISTOR AMPLIFIER CIRCUIT USING H PARAMETERS To form a transistor amplifier it is only necessary to connect an external load and signal source as indicated in Fig. Transistor in any one of the three possible configurations. We treat the general case its small-signal hybrid model. THE TRANSISTOR IS REPLACED BY ITS H-PARAMETER MODEL THE CURRENT GAIN(AI): Forthetransistor amplifierstage,aiisdefinedas the ratio of output to input currents, THEINPUTIMPEDANCEZI: The resistance Rs, represents the signal-source resistance. The impedance we see looking into the amplifier input terminals (1, 1') is the amplifier input impedance Zi, Fromthecircuitofwehave Fromtheinputcircuit So,

19 But THEVOLTAGEGAIN/ VOLTAGEAMPLIFICATION, A V The ratio of output voltage V 2 to input voltage V 1 gives the voltage gain of the transistor, So, But, So, Y L is Load admittance THEOUTPUTADMITTANCEY O : For the transistor in Y o is defined as But, So,..(1) As, Vs=0, so from input loop we can write POWER GAIN AP: Ratio of output power to the input power is known as Power gain. A p = P 2 /P 1 A p = V 2 I 2 /V 1 I 1 A p =A v *A i Putting this value in equ (1)

SUMMARY: SMALL-SIGNAL ANALYSIS OF A TRANSISTOR AMPLIFIER EXAMPLE: FIND THE H PARAMETERS OF THE CIRCUIT SHOWN IN FIG. Solution.

It is clear that input impedance of the circuit is 10 Ω because5ωresistanceisshortedout.

Under this condition, there will be no current in 10Ω resistor and, therefore, there can be no voltage drop across it.

5 X10-4,h 21 = 50,h 22 = 25µA/V. If R L = Rs, = 1,000 Ω, find the various gains and the input and output impedances.

20 SUMMARY: SMALL-SIGNAL ANALYSIS OF A TRANSISTOR AMPLIFIER EXAMPLE: FIND THE H PARAMETERS OF THE CIRCUIT SHOWN IN FIG. Solution.The hparametersofthecircuitcanbefoundasbelow. Tofind h 11 and h 21, short - circuittheoutputterminals. It is clear that input impedance of the circuit is 10 Ω because5ωresistanceisshortedout.andi 2 =-i Tofind h 12 and h 22,opencircuittheinput, Note that input terminals are open. Under this condition, there will be no current in 10Ω resistor and, therefore, there can be no voltage drop across it. EXAMPLE: The transistor is connected as a common-emitter amplifier, and the h parameters are h 11 =1,100 Ω, h 12 = 2.5 X10-4,h 21 = 50,h 22 = 25µA/V. If R L = Rs, = 1,000 Ω, find the various gains and the input and output impedances. Solution: In making the small-signal analysis of this circuit it is convenient, first, to calculate Ai, then obtain Ri from Ai, and Av from both these quantities. Now the output impedance looking into the output terminals with input terminalsopenissimply5ω

21 81 82 SMALL SIGNAL ANALYSIS OF JUNCTION TRANSISTOR Small Signal Analysis means, we assume that the input ACsignalpeaktopeaktoamplitudeisverysmallaround theoperatingpointqasshowninfig. The swing of the signal always lies in the active region, andsotheoutputisnotdistorted. In the Large Signal Analysis, theswingoftheinputsignalis over a wide range around the operating point. The magnitude of the input signal is very large. Because of this the operating region will extend into the cut-off region 83 and also saturation region. METHOD FOR ANALYSIS OF A TRANSISTOR CIRCUIT In the Previous section we have seen generalized transistor circuit analysis using H-parameters. There are many transistor circuits with different biasing and configuration. The analysis of such transistor circuits for its small signal behaviour can be made by following simple guidelines

22 SIMPLE GUIDELINES. Draw the actual circuit diagram. Replace coupling capacitors and emitter bypass capacitors by short circuit ReplaceDCsourcebyashortcircuit. ShortVccandgroundlines Mark the points B,C,E on circuit diagram and locate these points as the start of the equivalent circuit. Replace the transistor by its H parameter model

23 EXAMPLE ConsiderasinglestageCEamplifierwithR s =1K,R 1 =50 K,R 2 =2K,R c =1K,R L =1.2K,H fe =50,H ie =1.1k,H oe =25µA/V and H re = , as shown in fig. Calculate various gain and impedances

24 93 94 EXAMPLE In CC amplifier transistor parameters are H fc = -101, H ic =1.2k,H oc =25mA/V and H re =1, Calculate the Ri, Ro, Av, Ai

26 PRACTICEEXAMPLE: ForthecircuitshowninFig.belowestimate Ai, Av, Riand Ro.The h-parametersforthetransistoraregivenas hfe = 100, hie = 2000,and hreisnegligibleand hoe = 10-5 mhos. & I b =0.1mA EQUIVALENT H PARAMETER MODEL: 103 LIMITATIONS OF H PARAMETERS The h parameter approach provides accurate information regarding the current gain, voltage gain, input impedance and output impedance of a transistor amplifier. However, there are two major limitations on the use of these parameters. (i)itisverydifficulttogettheexactvaluesof hparameters for a particular transistor. It is because these parameters are subject to considerable variation unit to unit variation, variation due to change in temperature and variation due to change in operating point. Inpredictinganamplifierperformance,caremustbetakentouse h parameter values that are correct for the operating point being considered. (ii) The h parameter approach gives correct answers for smalla.c.signalsonly.itisbecauseatransistorbehavesasa104 linear device for small signals only. 26

27 QUESTIONS

BJT. Bipolar Junction Transistor BJT BJT 11/6/2018. Dr. Satish Chandra, Assistant Professor, P P N College, Kanpur 1

BJT. Bipolar Junction Transistor BJT BJT 11/6/2018. Dr. Satish Chandra, Assistant Professor, P P N College, Kanpur 1 BJT Bipolar Junction Transistor Satish Chandra Assistant Professor Department of Physics P P N College, Kanpur www.satish0402.weebly.com The Bipolar Junction Transistor is a semiconductor device which