Electronic Circuits Laboratory EE462G Lab #8npn Bipolar Junction Transistornpn BJT Operationnpn BJT CharacteristicsDC (Biasing) ModelDC (Biasing) Equivalent ModelLoad Line Analysis:Large-Signal (DC) ModelBJT AmplifierBJT Amp Small-Signal ModelSlide 11BJT Circuit ParametersTaylor SeriesSPICE ExampleSlide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Electronic Circuits LaboratoryEE462GLab #8BJT Common Emitter Amplifiernpn Bipolar Junction TransistorBJT in a common-emitter configuration+VBE_+VCE_CBEBB – BaseC – CollectorE – EmitterFor most applications the BJT is operated in the active region where:pnnBCEBECEBEVVV  and V60.npn BJT OperationBJT in a common-emitter configuration in active region (VCE > VBE ~ .6V):+VBE_+VCE_CBEThe pn junction for VBE is forward biased and current iBE flows according to the Shockley equation:nn 1TBEESEVVIi expwhere VT  .26 mV and IES ranges from 10-12 to 10-17. Electrons from the emitter flow into the base and are pulled into the depletion region of the reversed biased collector-base junction.iE-----+++++(-)npn BJT CharacteristicsBJT Transfer Characteristics in active region with  = IC / IB = 100:0 0.2 0.4 0.6 0.8 100.20.40.60.81x 10-5Volts (VBE)Amps (Base Current)0 1 2 3 4 5 6 7012345x 10-4Volts (VCE)Amps (Collector Current)IB = 4 microamps IB = 3 microamps IB = 2 microamps IB = 1 microamp1DC (Biasing) ModelEquations for the DC operating point,assume IB <<<< I2:212RRRVVCCBB R1R2RCREVCCVBBIBBECICIEI2EECECCCCRIVRIV BCIIEBCIII Key Result (Load-line Equation):ECCEECCCCRRVRRVI11 How sensitive is Ic to changes in ?R1R2RCREVCCVCCDC (Biasing) Equivalent ModelApply Thévenin model to base terminal:212RRRVVCCB2112RRRRRBLoad-Line EquationEBBEEBBBRRVRRVI)()(11VB RCRERBIBVCCLoad Line Analysis:0 0.2 0.4 0.6 0.8 100.20.40.60.81x 10-5Volts (VBE)Amps (Base Current)0 1 2 3 4 5 6 7012345x 10-4Volts (VCE)Amps (Collector Current)IB = 4 microamps IB = 3 microamps IB = 2 microamps IB = 1 microamp1 EBBRRV)( 1BVECCCRRV1CCVQualitatively describe what happens in both curves when  increases(or decreases).Large-Signal (DC) Model VBVBEVCCRBRCREIBIBICIEBEC R1R2RCREVCCVBBIBBECICIEI2BJT AmplifierOnce the DC operating point is set, the AC input and output are coupled to the amplifier with capacitors so as not to perturb the operating point. vsRsCinR1R2RCRECoutCERLVCCBJT Amp Small-Signal ModelConsider the capacitors as short circuits for the small signal AC and open circuit for DC to obtain the model below. The resistor ro accounts for the small slope of the I-V characteristics in the forward-active region (often assumed to be infinite). The resistance r is found from linearizing the nonlinear base-emitter characteristic, which is an exponential diode curve. 2112RRRRRBRsvsriBBCEroRL+vin-iB+vout-RCRBBJT Amp Small-Signal ModelDetermine the voltage gain. How would the emitter resistor affect the gain if it was not bypassed? RsvsriBBCEroRL+vin-iB+vout-RCRBRE replaces the short here!BJT Circuit ParametersHow can  be found experimentally using the curve tracer?How can the input and output resistances be determined experimentally?How can voltage gain be determined experimentally?Taylor SeriesRecall that a function can be expressed as a polynomial through a Taylor Series expansion:where a is a point about which the function is expanded. Note that if a represents a quiescent point for a voltage, then the reciprocal of the coefficient first linear represents the small signal impedance. axaxdxxfdaxdxxd faxafxf222)(!2)()(!1)()()(SPICE ExampleThe amplifier circuit can be constructed in B2SPICE using the BJT npn (Q) part from the menu. The “edit simulation model” option can then be used to set the “ideal forward beta”The input can be set to a sinusoid at desired frequency and amplitude for a transient analysis.SPICE can also do a Fourier analysis to observed effects of clipping and distortion. There should be no harmonic energy for perfect amplification.SPICE ExampleExample circuit with meters to monitor input and output:Q1beta= 100 R110KR25kR31KV112R550R4600C11uV20C21uC31uR61KIVm1IVm2SPICE ExampleGraphic output for .03 V sine wave input (IVM1) at 10 kHz. Output is shown for meter IVM2. What would the gain of this amplifier be at 10 kHz?bjtexamAC-Transient-0-GraphTime (s)0.0 200.000u 400.000u 600.000u 800.000u 1.000m(V)-200.000m0.0200.000mmax:355.280u, 0.286min:405.280u, -0.291max:625.280u, 0.00981min:675.280u, -0.00980TIME 586.280u v(IVm1) -7.532m v(IVm2) -107.794mD(TIME) 0.0 D(v(IVm2)) 0.0SPICE ExampleFourier analysis of output. Frequency magnitude plot for output at meter IVM2. Where should the energy be in the frequency domain for this output?bjtexamAC-Fourier-0-GraphFrequency (Hz)0.0 20.000k 40.000k 60.000k 80.000k0.0500.000mfreq -1.000 norm_mag_v8 -1.000 D(freq) -7.623D(norm_mag_v8) -1.000SPICE ExampleGraphic output for .08 V sine wave input (IVM1) at 10 kHz. Output is show for meter IVM2. What would the gain of this amplifier be at 10 kHz?bjtexamAC-Transient-1-GraphTime (s)0.0 200.000u 400.000u 600.000u 800.000u 1.000m(V)-2.000-1.0000.01.000max:560.280u, 1.971min:603.280u, -2.396max:725.280u, 0.0785min:775.280u, -0.0782TIME 709.280u v(IVm1) 42.303m v(IVm2) -2.217D(TIME) 0.0 D(v(IVm2)) 0.0SPICE ExampleFourier analysis of output. Frequency magnitude plot for output at meter IVM2. Where should the energy be in the frequency domain for this output?bjtexamAC-Fourier-2-GraphFrequency (Hz)0.0 20.000k 40.000k 60.000k 80.000k0.0500.000mfreq -1.000 norm_mag_v8 -1.000 D(freq) -5.780D(norm_mag_v8) -2.653MegSPICE ExampleGraphic output for 1.2 V sine wave input (IVM1) at 10 kHz. Output is show for meter IVM2. What would the gain of this amplifier be at 10 kHz?bjtexamAC-Transient-3-GraphTime (s)0.0 200.000u 400.000u 600.000u 800.000u 1.000m(V)-4.000-2.0000.02.000max:539.280u, 2.434min:610.280u, -4.323max:833.280u, 1.040min:875.280u, -1.166TIME 850.280u v(IVm1) -4.199m v(IVm2) 2.322D(TIME) 0.0 D(v(IVm2)) 0.0SPICE ExampleFourier analysis of output. Frequency magnitude plot for output at meter IVM2. Where should the energy be in the frequency domain for this output?bjtexamAC-Fourier-3-GraphFrequency (Hz)0.0 20.000k 40.000k 60.000k 80.000k0.0500.000mfreq -1.000 norm_mag_v8 -1.000 D(freq)