INTRODUCTION TO ELECTRONICS
INTRODUCTION TO ELECTRONICS EE 329
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This 18 page Class Notes was uploaded by Amara Morar on Monday October 12, 2015. The Class Notes belongs to EE 329 at Idaho State University taught by Staff in Fall. Since its upload, it has received 32 views. For similar materials see /class/222196/ee-329-idaho-state-university in Electrical Engineering at Idaho State University.
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Date Created: 10/12/15
CH 40 BASIC BJT AMPLIFIERS In the last chapter we described the operation of the bipolar junction transistor and analyzed and designed the dc response of circuits containing these devices In this chapter we emphasize the use of the bipolar transistor in linear ampli er applications Linear ampli ers imply that we are dealing with analog signals A linear ampli er then means that the output signal is equal to the input signal multiplied by a constant where the magnitude of the constant of proportionality is in general greater than unity A linear ampli er is capable of producing signal power gain that is the power in the output signal is greater than the power in the input signal We will investigate the source of this quotextraquot power We examine the properties of three basic singlestage or singletransistor ampli er circuits These circuits are the commonemitter emitterfollower and commonbase con gurations These con gurations form the building blocks for more complex ampli ers so gaining a good understanding of these three ampli er circuits is an important goal of this chapter We introduce a few of the many possible multistage con gurations in which multiple ampli ers are connected in series or cascade to increase the overall smallsignal voltage gain or to provide a particular combination of voltage gain and output resistance Our discussion includes the method of analysis required for these types of circuits and a synopsis of their proper es 41 ANALOG SIGNALS AND LINEAR AMPLIFIERS In this chapter we will be considering signals analog circuits and ampli ers A signal contains some type of information For example sound waves produced by a human contain the information the person is conveying to another person Our physical senses such as hearing vision and touch are naturally analog Analog signals can represent parameters such as temperature pressure and wind velocity Here we are interested in electrical signals such as the output signal from a compact disc a signal om a microphone or a signal om a heart rate monitor The electrical signals are in the form of timevarying currents and voltages Timevarying signals from a particular source very o en need to be ampli ed before the signal is capable of being quotusefulquot For example Figure 41 shows a signal source that is the output of a compact disc system That signal consists of a small timevarying voltage and current which means the signal power is relatively small The power required to drive the speakers is larger than the output signal from the compact disc so the compact disc signal must be ampli ed before it is capable of driving the speakers in order that sound can be heard Other examples of signals that must be ampli ed before they are capable of driving loads include the output of a microphone voice signals BB 329 Introduction to Electronics 147 CD pln r Low signal pm er Block diagram at a compact disc prayer system Figure 41 e e A We WantLhe uutput ampli er The m is a dc The pnn ple uf mm V V respunsexsthe sum ufmem mmmdual rewunses 42 THE BIPOLAR LINEARAMFLIFIER Bxpulzr In Chapter 6 a 29 xmqme mcmms chamdmsucs developed 1n the diapha Fxgure 4 23 Qwwa VII m1 Q m IbrwArdncmc mgmn V 77 n 4 1 Q p31 1 1 9111 mmmlmn V I n 1 r 1 1 1 1 V a a b 1 1 A Figure 42 a Bipolar Iransvslur invener circuit 1 1nvener transfer charadenstics h wmmh Emma A 1 r W T volmge Thusweno longer have an amph a 11 than mu 1da1 Table4 E15329 Immductmnm Ekc mnlcs 149 Table 41 Summary of notation Variable Meaning i5 VB Total instantaneous Values 3 BE DC Values Im quotM Instantaneous ac Values I V hasor values 421 Gmphiizl Analysis and AC mum Circuit smusmdal 513121 suurce FigurEO a A nnmmnnrkmi el mm with mermytng signal source m senas mm the base a source a 29 mm th mcmms Figure 44 shows menansisor charadeiistics dc load line and are Qpoim Timr it E Figure 44 Cummmnremmer transistor characteristics dc load line and sinusoidal varialian in base current collectar mum and colleclurremmer valiags which quot 39 moutpltvoltaggin Emmy mm the draiii is an ampli er Tomeetthis oljec ve are small enough to yieldlinear relau39oris The concept ofquotsmall enalghquot or small s39gnal will be disalssed mruier mem m r E 329 lnimrlumiuniu Eledmmcs lsl nential relationship betweenbasecun mtandbaseemittervoltage l 510139 7 n Time Figure 45 sinusoidal signms slope omne curve atthe QpoinL Using Figure 45 we can now detennine one quantitative de ninon ofmz signal The mla onbdwem BE voltage andbase curmnt is E 329 xnuoaucuonm Elemamcs 152 m m pal 41 If B is Compuscd of a dc arm with a alnuauldlll umnponcnl superimposed 39 7 l np emil 1 gt3 39 V 39 Q is nuimaily rcl39crrcd lo as lhe hase cmlllcr llunron vullnge V lun The lenn ISl m 1 exprWQm is lhe qulcal cnl hase ennenl so we can write VBEQ l vb lhu lc v WhCI L V l 1 I W 43 Thu 13 L CHI ICHL given in his form ulmnul bu wrlllcn as an llu CHI I Cnl anych impi cd 01 ille i enl value Ilewevei rm ltltV1mn we an expand llie expenenlinl leun m n Tllylol iies e p39 g only he lim ar term This approximation is whal is mennl by small signal We lhcn have 1U 1 mo W l in 1 l H 4401 l whcl c i is llie limevniying slnumldul hnse mlrrunl glvcn by vquot m 440 V has is Inthis casethetelm am be valid As a general iule ifvu is less than 10 mv men the exponenn39al ielan39on given by Equation 43 and its superimposed on do values We can then write E 329 IntruducnunluEle mmcs o 1 HQ 139 4501 139 1 it 415k L V011 Vtu 45M and BL Vat g 4 quot1w 45d H the signal some it iszuroi than the base cmillcrtu td collector emitter loop uqnalio Vim 1 an 39i39 Vut g 46a and VC ILQRL 39i V039 4mm Taking mm account the limt rvarying signals wt ml lhc hm emitter loop equation is Vim t H ilXRE at 473 Van r1lw HR1 ULKLQ 1 wt 47b Rearrangng terms we ind Vim quot wkx Vmsg 7 39M u 39i m 39 t 475 From Equation 46ai the left side of Equation 47L is zero Equation 47c can then be written as 7 I39M v in 48 which is the ba 39mittcl 100p equation with all dc tutms t nut to Zero Taking into ttccuunl the timervtu ying signals the collector emitter loop equation is Vat iCRr 1 rut 4 Q r i R IVU tQ rm 4901 Reananging terms we lind V IQR by 139qu i w 4 9a From Equation 4601 the left side of Equation 49b is zero Equation 49b can be written as ll RF H n 4 10 r 1 n t t 39 These EB 29 inundumanm Electmmcs w quot 39 39 humrummr rr rr 39 Weshouldstxess es and currents active region who the appropriate dc voltag npn transistor Figure 45 J 39 39 39 39 39 Lhe base and 39 39 39 quot1 V133 and v m m I 0quot s r r n n mm m m 1mm rival Inother m1 quot 411 Smallsignal Hybridr E quivalent Cirmit or the Bipolar Transistor shown in Figm 47 EB 29 Inkanhcuanm Eleckamcs Figure 47 The BJT as a smallsignal twoport network signals are small the smallsignal input voltage by 39m 39d the 2point parameters EE 329 IntruducnuntuEledmmcs quot been described 739 A The inverse of mo 39 a nan u u nuuau L39 L L r quot aw L L m L CL L 39 nun p r T 39A m 414m UV or i 3 4 W 4140 W my mum Chaplcr 3 wt had wrile I th cxp 415 V I g 415 1 n The arm alScx1vM VT cvalualcd at he Qrpoinl isjnal the cum 1 lcclur current The mm It I a conducmnec Smcc his mnduclanuc m1le 4 ullrrnnl in lhc cullcclur lo a vullagc in 11c 13 E cu39mul lhc pummultr 1 calm a uanscnndumanm and is wriucn gm 9 417 I n biascunent bipolar transistor as shown in Figure 48 EE 329 Intruducnun m Electmmcs 3m Do my Vm v V gt Figure 43 A simpli ed sma csigna hymen equivalem crrcu hr the npn transistor previously shown m Figure 4 s collector current to the smallrsxgqal base current We can wme A 77 k 7 All 41mm M W or i 418b 418m and is 31ch an incrcmcnlal or a mnlnluwmnllur ummnl gain VVL can lhcn wlilc 51139 419 39r39L H We Wm use both cucms m the Examples um follow m ths chapta39 EE 2 Immdmmm m Ekctmmcs Figure 49 an smartstgnat equivatem circqu using cammunremi ler current gain Rdz mhawazn up and u The dAffErence between these two tems ls xllustxated m Figure 410 39r39h a At might east ement andm an xdeal BJT these tems are ldmhca EE 2 Immdmonn tn Ekctmmcs Imam c A ms implies Lhatleakage emean are negligible Ifwe multiply n andgm we nd L VI 4 20 W V 19 Ingmeal the text eunem This vanauon with 1 Wm be mem ed on the data sheets am 11 phase notanon Figure411 The smauugna emvmm erJn of he comn39nnrumw cr mm usmg he npr Vanuatu hyb tdew n39ndm VeV5 sxgqalvolmge n t W or a 29 xmmm m Bantams 15m x 7 In Am mGr 421 and ham lhc mpm porlion of lhc circml we nd V 7 V 422 M 3 RB Thu mnII sigmxI vollugr gain is lhcn V r 7quot 7quot 3 A h gmh In 4 RB 4 2 EB 29 xmmancmn m Elecfmmcs Example 41 Ohiecii Calculats the smallzlgnll voltage gain 111 the bipolar u anslslur Cll Cull shown in l igure 4 1 Assume the ramislm and Cn Cull parameters are 3 1001 VCC 12V V 07V1R526k R I V DC solution We rst dd the dc analySis tu nd the Q point values We obtain 7 39 7 HQ Tm 500 7 a 111 lA so that m tiiw 10011031Agt1mA Then mg Vccilcgkc 1271u iv Tlierelore the translator is biased in the Forward active mode in Solution The smallsignal hybrid Jr parameters 2r 397 rw mg 150 1 and pg 1 7 1 7 0026738Ql AV Th Small itnui voltage gain i3 determined using the sma Slgn ll equivalent circuit shown in rigure 4 11 From Equation 4 23 we nd A Vquot n 7 gmkf39 r 73x5a 50 7114 ma itutl nfthc hll luNKHdal input Comment W Ste that thc magnitude ofthc sinusmda output vulttigc IS 11 41mm thc volla A We will see 1121 other circuit cmifiguiatittm 0 result in exam larger sm lll Slgnzl tug P Discussion We may considcr u speci c sinumidul inpul nllugc v Lu in m V 39l39h ainumidiil bane currenl ls gnen hy in L1 475 uu ml uA i In all The sil ulN UiLlill CUIlCL lm ciirrrnt i r 7 111 lllll47551n ml gt 11475unmimA and the siniisuidal wlleciorcmitler mliiigc IA rR11 7Ul75tgtin qu 71x sinun V E 329 inimduruuniu Eterirmics 162 Frgure A 12c N that moreases Frgure A m an m 519131 volmge Pmblemrsnlving mchniques rur bipnlar AC anzlsyis proceeds as follows 1 1 whxch forwardracnve reglon m 0139de produce a hnear amphfrer Z A The smallrsxgqal EB 29 xmmummn m Execmus m 3Alolll39l39lquotquot 39 mmium spouse ofthe cimuit w the timeVarying input signals only Table A 4 Mq i Eluucnl IA39 rammmmp m mndLI A model I i V RESISIOI R i R R R Capacitor 1 CV Open C o o I 7 V Short Inductor L 1L L Dmde ID Saw 7 1 1 VTID Independent Short voltage source Independent Open S consmnt current source Tnhlc suggcmd by Richard Hester of km sum Lniwrdt InTablezH L 4 4 quot isashortcimuiL 39 39 39 quot n 39n u I A I t p 1 39 oh 39 39 39 39 The mallsignal A and the independmt dc cun39mt source becomes an Open circuit 55329 Imamchmta eckamcs 154
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