Transistor switch amplifier a 3 terminalIncoherentSource Light Vein ArteryLight ValveGain medium.Dam Laser HeartEmitter CollectorIon ChannelBJT MOSFET Axonal conduction All of these share a feature with . Output current can toggle between large and small Switching Digital logic create 0s and 1s Small change in valve 3rd terminal creates Largechange in output between 1st and 2nd terminal Amplification Analog applications Turn 0 5 50 . Example BJT common emittercharacteristicsGain 300 http www computerhistory org ... timeline html 1940s. Aim of this chapter How can we get Gain What is the structure of the device to get gain What is the equation for gain How can we use this equation to maximize gain . How can we model this device as a circuit element What are its AC characteristics and speed Recall p n junctionVappl 0 Vappl 0Forward bias on P on N Reverse bias on N on P. Shrink W Vbi Expand W Vbi Allow holes to jump over barrier Remove holes and electrons awayinto N region as minority carriers from depletion region So if we combine these by fusing theirterminals .Vappl 0 Vappl 0Holes from P region Emitter of 1st PN junctiondriven by FB of 1st PN junction into central N region Base Driven by RB of 2nd PN junction from Base into P region of2nd junction Collector . 1st region FB 2nd RB If we want to worry about holes alone need P on 1st region For holes to be removed by collector base region must be thin Bipolar Junction Transistors BasicsIE I B I C KCL .VEC VEB VBC BJT configurations Bipolar Junction Transistors BasicsVEB VBC 0 VEC 0 but smallIE IC 0 IB 0 VEB VBC 0 VEC 0.IE IC 0 IB 0VEB 0 VBC 0 VEC 0IE 0 IC 0 IB 0 but small Bipolar Junction Transistors BasicsBias Mode E B Junction C B Junction.Saturation Forward ForwardActive Forward ReverseInverted Reverse ForwardCutoff Reverse Reverse BJT Fabrication. PNP BJT Electrostatics PNP BJT Electrostatics NPN Transistor Band Diagram Equilibrium PNP Transistor Active Bias Mode.Few recombinein the baseCollector Fields drive holesfar away where they can treturn thermionically.Large injection Most holesof Holes diffuse to Forward Active minority carrier distributionnE x nC0nC x . PNP Physical Currents PNP transistor amplifier actionIN small OUT large Clearly this works in common emitter.configuration Emitter Injection Efficiency PNP I E I Ep I En Can we make the emittersee holes alone .0 1 Base Transport Factor0 T 1 Can all injected holesmake it to the collector Common Base DC current gain PNP.Common Base Active Bias mode IC DCIE ICB0ICp TIEp DC T T IE.IC T IE ICn Common Emitter DC current gain PNPCommon Emitter Active Bias mode IE DCIB ICE0IC DCIE ICB0 DC 1 DC . DC IC IB ICB0 GAIN IC DCIB ICB0 Common Emitter DC current gain dc 1 T.Thin base will make T 1Highly doped P region will make 1 PNP BJT Common EmitterCharacteristic.Title: Bipolar Junction Transistors: Basics Author: lrh8t Last modified by: Avik Ghosh Created Date: 11/4/2002 1:54:59 PM Document presentation format