Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Slide 71Slide 72Slide 73Slide 74Slide 75Slide 76Slide 77Chapter 4 – Bipolar Junction Transistors (BJTs)Introductionhttp://engr.calvin.edu/PRibeiro_WEBPAGE/courses/engr311/311_frames.htmlA simplified structure of the npn transistor. Physical Structure and Modes of OperationA simplified structure of the pnp transistor.Physical Structure and Modes of OperationPhysical Structure and Modes of OperationMode EBJ CBJActive Forward ReverseCutoff Reverse ReverseSaturation Forward ForwardCurrent flow in an npn transistor biased to operate in the active mode, (Reverse current components due to drift of thermally generated minority carriers are not shown.)Operation of The npn Transistor Active ModeProfiles of minority-carrier concentrations in the base and in the emitter of an npn transistor operating in the active mode; vBE  0 and vCB  0.Operation of The npn Transistor Active ModeThe Collector CurrentThe Base CurrentPhysical Structure and Modes of OperationiCISevBEVTiBiCISevBEVTiEiCiB 1iC 1ISevBEVT iC IE  1Operation of The npn Transistor Active ModeLarge-signal equivalent-circuit models of the npn BJT operating in the active mode.Equivalent Circuit ModelsThe Constant nThe Collector-Base Reverse CurrentThe Structure of Actual TransistorsCurrent flow in an pnp transistor biased to operate in the active mode.The pnp TransistorTwo large-signal models for the pnp transistor operating in the active mode. The pnp TransistorCircuit Symbols and ConventionsCBECBECircuit Symbols and ConventionsExample 4.1VCC 15 IC1 0.001  100 VBE 0.7 VEE 15 VT 0.025Design circuit such that VC 5 IC2 0.002RCVCC VCIC2 RC 5 103Since VBE=0.7V at IC=1mA, the value of VBE at IC=2mA isVBE 0.7 VT ln21 VBE 0.717VE VBE VE 0.717 1 IEIC2 IE 2.02 103REVE VEE( )IE RE 7.071 103iCISevBEVTIBIC2 IB 2 105EBCExample 4.1IBIC2 IB 2 105Example 4.1Summary of the BJT I-V Relationships in the Active ModeiCISevBEVT iBiCISevBEVT iEiCISevBEVTNote : for pnp transitor, replace vBE for vEBiC iE iB1  iEiE 1iC iB iE 1 iB  iE  1VT 25mVExercise 4.8Exercise 4.9The Graphical Representation of the Transistor CharacteristicsThe Graphical Representation of the Transistor CharacteristicsTemperature Effect (10 to 120 C)The iC-vCB characteristics for an npn transistor in the active mode. Dependence of ic on the Collector VoltageDependence of ic on the Collector Voltage(a) Conceptual circuit for measuring the iC-vCE characteristics of the BJT. (b) The iC-vCE characteristics of a practical BJT.Dependence of ic on the Collector Voltage – Early EffectICISevBEVT 1vCEVAVA – 50 to 100VDependence of ic on the Collector Voltage – Early EffectNested DC SweepsExampleExampleExampleMonte Carlo Analysis – Using PSpice Monte Carlo Analysis – Using PSpice Monte Carlo Analysis – Using PSpice Probe Output Ic(Q), Ib(Q), Vce Monte Carlo Analysis – Using PSpice (a) Conceptual circuit to illustrate the operation of the transistor of an amplifier. (b) The circuit of (a) with the signal source vbe eliminated for dc (bias) analysis.The Transistor As An AmplifierTheCollectorCurrentandTheTransconductanceTheBaseCurrentandtheInputResistanceattheBaseTheEmitterCurrentandtheInputResistanceattheEmitterLinear operation of the transistor under the small-signal condition: A small signal vbe with a triangular waveform is superimpose din the dc voltage VBE. It gives rise to a collector signal current ic, also of triangular waveform, superimposed on the dc current IC. Ic = gm vbe, where gm is the slope of the ic - vBE curve at the bias point Q. The Transistor As An AmplifierTwo slightly different versions of the simplified hybrid- model for the small-signal operation of the BJT. The equivalent circuit in (a) represents the BJT as a voltage-controlled current source ( a transconductance amplifier) and that in (b) represents the BJT as a current-controlled current source (a current amplifier). Small-Signal Equivalent Circuit ModelsTwo slightly different versions of what is known as the T model of the BJT. The circuit in (a) is a voltage-controlled current source representation and that in (b) is a current-controlled current source representation. These models explicitly show the emitter resistance re rather than the base resistance r featured in the hybrid- model.Small-Signal Equivalent Circuit ModelsSignal waveforms in the circuit of Fig. 4.28.Fig. 4.30 Example 4.11: (a) circuit; (b) dc analysis; (c) small-signal model; (d) small-signal analysis performed directly on the circuit.Fig. 4.34 Circuit whose operation is to be analyzed graphically.Fig. 4.35 Graphical construction for the determination of the dc base current in the circuit of Fig. 4.34.Fig. 4.36 Graphical construction for determining the dc collector current IC and the collector-to-emmiter voltage VCE in the circuit of Fig. 4.34.Fig. 4.37 Graphical determination of the signal components vbe, ib, ic, and vce when a signal component vi is superimposed on the dc voltage VBB (see Fig. 4.34).Fig. 4.38 Effect of bias-point location on allowable signal swing: Load-line A results in bias point QA with a corresponding VCE which is too close to VCC and thus limits the positive swing of vCE. At the other extreme, load-line B results in an operating point too close to the saturation region, thus limiting the negative swing of vCE.Fig. 4.44 The common-emitter amplifier with a resistance Re in the emitter. (a) Circuit. (b) Equivalent circuit with the BJT replaced with its T