‘Unit-3 ‘Analog Electronics SEMICONDUCTOR DIODE: ‘Te semiconductor diodes formed by simply bringing P-ype and N-type materials together (constted om the sme base Ge oS) At be instant the two materials are “oie” the elects and holes inthe region ofthe junction wil combine, resuling a2 lack of caer inthe region nea the junction ‘This region of uncovered pestve and negative ions i clle the depletion region due othe depletion of carries in his elon Since he diode is «two-teminal devi, the application ofa voltage across ts terminals leaves three possibilities: no bias (V0), forward bis (V0 V), and reverse bias (VV). sch contin tht wil result in respons hat the usr must ley understand if the device is tobe apple ffcively,Construction and opertion; No Applied Bas (V,-0 V): ‘Under no-biss (no applied voge) conditions, any minority cries hoe) in he type material tat find themselves within the depletion region wl pass directly {nto the pype mara ‘The close the minority cae isto the junction, the gre the atraction fa he Iyer of epive ons and else the opposion of the postive ons inthe depletion pon ofthe ape mara “The mort caer (electons of the n-ype material must overcame the atctve forces of the layer of positive ios inthe s-ype material andthe shield of egtive fons in the p-type materi o migrate ito the area beyond the depletion region ofthe ptype materi ‘However, the numberof majority carer sso large in the n-ype material that there wil invariably be a small numberof jority caer with sient kine ‘energy pss through the depletion region imo the paype mate Inthe sbsene of an applied bias voltage, the net Nw of charge in anyone direction for a semiconductor diode is 2Reverse-ias Condition (Vy <0): an extemal potential of V vols is applied across the pa junction such thatthe positive terminalis connected 10 the n-type material andthe negative terminalis ‘connected tothe p-type materia ‘The numberof uncovered postive ion inthe depletion region ofthe e-ype material wil increase dv tothe large numberof “fe” electrons daw fo he postive pote ofthe apped voltage or similar esos, the number of uncovered negative ions wilnceasein the p-type mari The nt lfc, therefore, i widening of the depletion epion ‘This widening ofthe depletion egon willesablish oo grea bri forthe majority carers to overcome fetvely reducing the majority car ow to 0 yvard-ias Condition (V,>0): +A forvard-bias cr“ condition is established by applying the pose potential othe pype materi und the negative potential othe mye material +The aplication ofa forwar-bias potential V, wll pressure elctons in the n-type material ard holes in he pype material o recombine With the ions nea the boundary nd rluce the width ofthe depletion reson ‘The resingminotiy-aer ow of electrons frm the pype materi othe n-4ype material (and of holes fom the ype material othe p-ype mater) has not hanged inmagnitue (sine the conduction eels coal primarily by the lined suber of impurities in he material), bul the reduction inthe wid ofthe depletion regio has resulted in a any majority low ars the jumetion. ‘An electron ofthe ype material now “sees reduced bare athe junction due othe reduced depletion region anda song atracion forthe postive potential applied to ‘the p-type material.‘Shc gut the ova an rene is eons Iy= ties" —1)| (ay a erste ene strane et Viste pl owl a ola aco te de ‘vane f hich foto fe pring contin an py Calman hata ge bree | ad pening owe ey of fa = wile ame mo hs et le trv ed) ‘The age Vin Bi (1) ele he ermal alge ad steed by ~ (3) eis Bam's om = 138 1072 Ty ste ae epee kins 73+ he eager C isthe magi of i change = 18 17°CLoadtne analysis: ‘The pple land wil aomally have an important impact onthe pot or region of operation of device the analysis is performed in a graphical manner, line can be drawn on he characters ofthe device that represents the apie load ‘The intersection ofthe lod ine wih the characteristics wil determine the point of operation ofthe system. Such an ans is, for obvious reasons, called loadin analy. ‘Consider the network shown below employing a diode having the characteristics. The “pressure essed by the batery iso esl a curreet hough he Series rit nthe elackwie drestion. Theft ht this current and the defied direction of condition ofthe dade ae mach” revels hat the didi in the “on state ‘nd conduction hasbeen established. The esting polity arosthedde wl be as shown andthe First quakat (and postive) of plying Kies voltage aw othe sere ui wil est in 4E-Vp— MeO E=Vo+ oR ooThe intsetons of he bad tne on he chats ca csly be detec iene simply employs te Gt tat anywre on he Kriz as J, © A iy onthe veil aa p89 sii lone 140 i 111; =0V m eqtion B= p+ Dk = 0V + i9R z 0 Rho Why 0A in equation 1 = V0 + AW Vo = Blig~0n(GRD Far cd cig Fg Pacing ec tats Fg 28 eae agile s her Han We=kean= WY ‘The rehing a in ape tig 24 The ern etc el ad Sitar ewne Lem oe Gee ; Vg am eee Te ism, ‘Theta Vp ean atime athe ary med tenes EEA def cur) wel a tt oleh aad TET ov ony anyRectifier A rectifier is a device that converts an oscillating two-directional altemating current (AC) into a single-directional direct current (DC). Mainly used in power supply to convert AC to DC. * Half wave rectification +6{i Sketch the output sand determine the de level of the output for the network of Fig. 2-49, Repeat art (ay tne idea! dade replace com diode. Repeat are rennet Sind compare solutions using Eas. s+ + ic 249 Nenwoet for tmapte 2 10 Soneeton: 2 Ie the situation the doe will conduct during the negative part of the input ax show sn ig. 2 SO. und v,, will apprear ax shcrwe in the ware Figure, Few the full povioal the ke level ric. 250 Arian var the stevia of Bamape 2.16 1b. Fora silicon diode. the output has the appearance of Fig. 2.51 andFull wave Rectification : Bridge ee alto ter a eS ins pit er eoFic. 2.57 npr and tpt waveforms for fall wave rectifier. Since the area above the axis for one fall cycle snow twice that obtained fora half-wave syst, the de lvel bs shea boom docbled snd Vac = 2(4.(2.7)] = 20.318Vq) or Vac = 0636 Vn] woe (2.10)[silicon rather than ideal diodes are employed as shown in Fig. 2.58. the application of Kirchhoff’ voltage law around the conduction path result in Wa Ve-te— Ve =0 and, Ye = Ve Determining Vp, for silicon diodes tn the bridge configuration ‘The peak value of the output voltage ¥, is therefore Venus = Va ~ 2M For situations where Vq >> 2Vg. the following equation can be applied for the average ‘value witha relatively high level of accuracy: Vac = 0636(V_ — 25) (uyFull wave Rectification :Center tapped TransformerClippers Clippers are networks that employ diodes to “clip” away a portion of an input siguat without distorting the remaining part of the applied waveform. Series Clippers For analyzing the networks 1. Take careful note of where the output voltage is defined. 2. Try to develop an overall sense of the response by simply noting the “pressure” ‘established by each supply and the effect it will have on the conventional current direction through the diode. 3. Determine the applied voltage (transition voltage) that will result in a change of state for the diode from the “off” tothe “on” state. 4. Its often helpful to draw the output waveform directly below the applied voltage using the same scales for the horizontal axis and the vertical axis.Diode is “OFF” region Output voltage Diode is “ON” region ee w= OV Vope = Vm — VDetermine the output waveform for the sinusoidal input « vesy nt SV=0V ve=y+5VParallel a | Determine v, for the network «Biased Parallel Clippers (Ideal Diodes) 4 z “ : k ‘ P Wibol ty —=ToesClampers A clamper is a network constructed of a diode, a resistor, and a capacitor that shifts a waveform to a different de level without changing the appearance of the applied signal.vy ea orZener Diode > +a forward or reverse direction + -AZener diode is a silicon semiconductor device that permits current to How in either af * The diode consists of a special, heavily doped pon junction, designed to conduct in the reverse direction when a certain specified voltage is reached + The Zenet diode has a well-defined reverse-breakdown voltage, at which it starts conducting current, and continues operating continuously in the ‘everse-bias mode without geting damaged. ‘Additionally the voltage drop across the diode remains constant over a wide range of voltages, a feature that makes Zener diodes suitable for use in voltage regulation. Operation of Zener Diode: ‘Zener Diodes are normally used only inthe reverse bias direction. means thatthe anode must be connected to the negative side of the voltage source and the cathode must be ‘Arain difference between Zener diodes and regular silicon diodes isthe way they are used inthe cites, tis primarily used to regulate the circuit voltage as it has constant Vz ‘aire cymes in TR wil aus only asl change in Ve. Itmeans that a zener diode can be used as an alternate cutent path. The onstant Vz developed across the diode can then be applied toa load ‘Thus the load voltage remains at constant by altering the current flow through the Zener diode. nected 10 the positive side The V-I Characteristics of a Zener Diode can be divided (©) Forward Characteristics, to two partsForward Characteristics ‘The forward characteristics of a Zener diode is shown in figure. It is almost identical to the forward characteristics ofa P-N junction diode. Reverse Characteristics {As we increase the reverse voltage, initially a small reverse saturation current Io. Which is in A, will follow. This current flows due to the thermally generated minority carriers. At a certain value of reverse voltage, the reverse current will increase suddenly and sharply. This is an indication that the breakdown has occurred. This breakdown voltage is called as Zener breakdown voltage or Zener voltage and it is denoted by V,, nome Breakdown Vetage ‘tenewedmtenin | Forward Characteristics Reverse Characteristics of Zener DiodeThe value ofV can be precisely controlled by conzolling the doping levels of P and N regions a the time of manufacturing a Zener diode. Afer breakdown has occured. The voltage across Zener diode remains constant equal to V, Any increase in the source voltage will result in the inerease in reverse Zener current. The Zener current afer the reverse breakdown must be controled by connecting resistor R as shown in figure, This is «essential to avoid any damage tothe device due to excessive heating Zener Region and its importance Reverse breakdown of the zener diode operates in a region called zener region, as shown in figure. In this region the voltage across zener diode remains constant but curent changes depending on the supply voltage, zener diode is operated in this region when it is being used asa voltage regulator, The complete vst characteristics of zener diode is as shown in figure V-I Characteristics of Zener DiodePhotodiodes * Itis a form of light-weight sensor that converts light energy. into electrical voltage or current. Photodiode is a type of semi conducting device with PN junction. Between the p (positive) and n (negative) layers, an intrinsic layer is present. The photo diode accepts light energy as input to generate electric current. * It is also called as Photodetector, photo sensor or light detector. Photo diode operates in reverse bias condition i.e. the p - side of the photodiode is connected with negative terminal of battery (or the power supply) and n — side to the positive terminal of battery. + Typical photodiode materials are Silicon, Germanium, Indium Gallium Arsenide Phosphide and Indium {Ht R =a) Photodiode symbol ¥ @ow TT : T CI Cf Coo | ri at me TEPrrtTtyt 0 oar en 8 ST Fe. 1622 14 ra flat Vy = 30 Vr he pd of Fe 1830,Bipolar Junction Transistor Pere chet dane cietearenn sem mr atin enti een Tecra asi sy Spi AE ro i «Aen ecm: «Sarena ly ON oper nach + ingle cir ty OE rn mo ‘aphasia we ont meting dvs en hrm i ning ae ip amet ing song: ili en Ede hg Vr tii id 9. erie oy J sp, en 8 an mn ae Hv Wo base acne “ning Goo we “spar (ao devi «AS SBE Tumi Ores dev endive pm we cme ila a csi i om seit igi ah pend np 1 ak md chennai rapentn ited oie gl vi is be ae caches o'r ay 8 ci sanihape <1 msn eli Vie kin mck +. cp nce Sw cua ones se «3. Caaen ols Caf pons Cen Gab Voge GnTransistor Construction +The transistor isa three-layer semiconductor device consisting of either two n - and one p -type layers of material or two p~and one n-type layers of material. The former is called an npn transistor , and the latter is called a pop transistor, + ‘The proper de biasing is necessary to establish the proper region of operation for ac amplification. The emitter layer is. heavily doped, + with the base and collector only lightly doped. The outer layers have widths much greater than the sandwiched p - or n type material + the terminals have been indicated by the capital letters E for emitter, C for collector, and B for base. PNP Transistor NPN TransistorCommon Emitter Configuration u In the Common Emitter or grounded emiter configuration, the input signal is applied between the base, while the output is taken from between the collector and the emitter as shown, “This type of configuration isthe most commonly used circuit for transistor based amplifiers and which represents the “normal” method of bipolar transistor connection, “The common emitter amplifier configuration produces the highest current and power ain ofall the three bipolar transistor configurations, “This is mainly because the input impedance is LOW as itis connected toa forward-biased PN-junction, while the output impedance is HIGH as iis taken from a reverse-biased PN-junction,‘Then bipolar Junction transistors operate three different regions: ‘*Active region -transistor operates as an amplifier. ‘*Saturation region- the transistor is fully ON operating as a switch. ‘Cut off region- the transistor is fully OFF operating as a switch, sesseReEse Characters of ln raat the cent ee cong rti: a ellctor characte: hae chartriienBJT load line analysis Vee = Vee ~ IcRe IF we choose Icto be OmA, Vee = Veo — (OR Ver = Veclic~0ma If we now choose Vcpto be OV, 0 = Vee ~ eRe Me gee Re lWer=ovField Effective Transistor (FET) * The field-effect transistor (FET) is a three-terminal device used for a variety of applications. *The are many similarities and difference between the FET and BJT devices, there are * The similarities are both devices are 3 terminal. * The primary difference between the two types of transistors is the fact that: * The BJT transistor is a current-controlled device. * The FET transistor is a voltage-controlled device. *There are npn and pnp bipolar transistors. * There are n-channel and p-channel field- effect transistors. * BJT transistor is a bipolar device—the prefix bi indicates that the conduction level is a function of two charge carriers, electrons and holes. * The FET is a unipolar device depending solely on either electron (n channel) or hole(p -channel) conduction.+ One of the most important characteristics of the FET is its high input impedance. * Typical ac voltage gains for BJT amplifiers are a great deal more than for FETs. * FETs are more temperature stable than BJTs, and FETs are usually smaller than BJTs, making them particularly useful in integrated-circuit (IC) chips. There are three types of FETs: JFETs, MOSFETs, and MESFETs. MOSFETs are further broken down into depletion type and enhancement type.Junction Field Effective Transistor JFET is a three-terminal device with one terminal capable of controlling the current between the other two. +The basic construction of the n-channel JFET, the major into) part of the structure is the n-type material, which forms | the channel between the embedded layers of p-type material. The top of the n-type channel is connected through an ohmic contact to a terminal referred to as the drain(D), whereas the lower end of the same material is connected through an ohmic contact to a terminal referred to as the source(S). The two p-type materials are connected together and to the gate(G) terminalVGS = 0 V, VDS Some Positive Value 1 1 r I ' I i 1 I 1 % Fic. 65 JPET at Veis = 0 V and Viys > 0 V. Varving reverse-bias potentials across Ws.07 ‘the pom junction of an n-channel JFET. Ip versus Vosfor Ves =OV.Pinch-off voltage 2 > FIG. 6.14 JPET symbols: (a) n-channel: (b)pochannel Fic. 68 Pinch-ety Was 0 V. Vos Veh loss is the maximum drain current for a JFET and is defined by the conditions Ves = 0 Vand Vos > IVPIVGS<0V 3 i FG.6.11 Fic. 6.10 ‘Channel JEET characteristics with Ings = 8 mA and Vp = —4 V. Application ofa negative voltage 10 the ate of a JFET. veer aad ~P-type DevicesSeay ws Wee vas te da can aN ein sat pit te [ean pom] ws Vas versus Ip Using Shockley's Equation Vos lo ° oon 03%, Soas/2 O5vp Joss/4 ve Oma ma N= fic. 617 Obani the amare from he dam character,Metal oxide semiconductor FET (MOSFET) n-Channel Depletion-Type MOSFET Construction When Ves=0V ae Chanel depletion pe MOSFET Rc.625 Chane depletion ope MOSFET with Vg =O Vand ape voltae Vogep -Channel Depletion-Type MOSFET symbolsyocons HO mA)(A + 0.287 = (10mA)(1 $628) rr chart fora chal depletion pe MOSFET wth lp ~ Ima and p= 4,