ObjectiveMaterialsProcedureFrequency Response of Common Emitter AmplifierMiller EffectOutput CapacitanceCommon Collector AmplifierUNIVERSITY OF CALIFORNIA AT BERKELEYCollege of EngineeringDepartment of Electrical Engineering and Computer SciencesEE105 Lab Exp er imentsExperiment 7: Frequency Respo nse1 ObjectiveYou have alre ady seen the performance of several BJT amplifiers. These were designed to ope rate well atcertain small-signal frequencies, and indeed there is a frequency limit imposed by the parasitic capacitancesof BJT devices. In this lab, you will observe how an amplifier responds to different input frequencies, makinguse of the National Instrument Bode Analyzer software. This lab will help familiarize you with the nativecapacitances in a tr ansistor, a nd how the frequency response is affected by these capacitances and externalloads as well.2 MaterialsComponent Quantity2N4401 NPN BJT 210 kΩ resistor 11 kΩ resistor 151 Ω resistor 11 nF Capacitor 1Table 1: Components used in this lab3 Procedure3.1 Frequency Response of Common Emitter Amplifier1. Construct the common emitter amplifier as shown in Figure 1. Use a 10 kΩ resistor for RCand a 51 Ωresistor for RS.2. Use a function generato r to generate a sinusoidal signal with amplitude of 25 mV, frequency of 1 kHz,and DC offset of 580 mV. This signal is both VBI ASand vincombined. We call this signal (VBI AStogether with vin) vIN. Note: You may notice some nonlinear effects on the output waveform. This isdue to the high input signal amplitude that we are using. We choose this amplitude to avoid the noisefrom the oscilloscope messing up our Bode plot measurement in a later step.3. What is IBI ASand the DC voltage at vOU T?4. Using the oscilloscope, plot input vINon Channel 2 and output vOU Ton Channel 1. Ma ke sure totransfer the waveforms over to the Lab Report.5. What is the gain magnitude and phase of vOU T/vINmeasured from the oscilloscope?13 PROCEDURE 2−+VBI AS−vin+RSVCC= 5 VRCIBI ASvOU TFigure 1: Common emitter amplifier test setup6. Instead of using the oscilloscope to measure both the gain magnitude and phase of vOU T/vINat otherfrequencies manually by examining the waveforms, let’s use NI Bode Analyzer software to automatethe process. To avoid errors fr om the software, make sure you follow the instructions below to set upthe software :• Make sure that vINis on Channel 2 and vOU Tis on Channel 1.• Connect the Trigger Output from the function g e nerator to the External Trigg e r port of theoscilloscope.• Open NI Bode Analyzer.exe from the computer des ktop.• When both the function generator and the oscilloscope are turned on, click “Refresh” under“Resource Name”.• The function generator is c onfigured to a higher GPIB address than the oscilloscope. Select theGPIB device with a higher GPIB address for the function generator, and select the GPIB devic ewith a lower GPIB address for the oscilloscope.• Set the stopping frequency at 2 MHz for this measurement. You can leave the starting frequencyat its default value.• Set the amplitude of the input signal to 25 mV, and the DC offset to 290 mV. Note: We set theDC offset to 29 0 mV because the function generator outputs an offset that is twice as much.• Hit “Run”! The software will start sweeping the input across different fre quencies to generate aBode plot.7. After the software is done plotting the Bode plot, you can drag the cursor on the plot to read out thegain magnitude and phase at different frequencies. Drag the cursor to around 1 kHz. What is the gainmagnitude and phase obtained with the software? How different is this measurement compared to theone obtained with the oscilloscope?8. Now drag the cursor to a point where the gain decreases by 3 dB. This will be the dominant pole of thisamplifier. What is the pole frequency? What is the phase at this frequency? Is the phase consistentwith the ma gnitude? (Recall that at the 3 dB point, the phase is 45◦away from the phase before the3 dB point)9. You can e xport the plot by right clicking on the plot, and then select “ Export Simplified Image”. Youcan also export the data points as .csv file by clicking the Export button. Print the plot out and turnit in with your Lab Report. You do not have to find the second pole because it is at too high of afrequency that our equipments cannot handle.3 PROCEDURE 3−+VBI AS−vin+RSCMVCC= 5 VRCIBI ASvOU TFigure 2: “Miller” c apacitor test setup3.2 Miller Effect1. The Miller effect ca n b e best examined by introducing a “Miller” capacitor across the gain. Le t’s takea look at the impact of Miller effect by adding a 1 nF capacitor for CMas shown in Figure 2.2. Repeat the above procedures on using the NI Bode Analyzer to find the frequency response of thisamplifier, but set the stopping frequency at 500 kHz. Attach the Bode plot to the Lab Report.3. How is the dominant pole of this amplifier compa red to the dominant po le of the previous amplifier?Is this expected?4. In this amplifier, we are using a 1 nF capacitor to simulate a large base-collector capacitor (CBC). Ifwe are to design an amplifier with high bandwidth, is a tra nsistor with high CBCdesirable?3.3 Output Capacitance1. Let’s examine the impact of output capacitance on a common emitter amplifier. Take out the “Miller”capacitor CMfrom Section 4.2, a nd place it at the output as shown in Figure 3.−+VBI AS−vin+RSVCC= 5 VRCIBI ASvOU TCMFigure 3: Output capacita nce test setup2. Repeat the above procedures on using the NI Bode Analyzer to find the frequency response of thisamplifier, but also set the stopping frequency at 500 kHz. Attach the Bode plot to the Lab Repor t.3 PROCEDURE 43. How is the dominant pole in this amplifier compared to the dominant pole of the previous two ampli-fiers? Is this expe c ted?3.4 Common Collector Amplifier−+VBI AS−vin+RSVCC= 5 VvOU TRE1kΩFigure 4: Common collector amplifier test setup1. The common collector amplifier is a wide bandwidth amplifier. Let’s examine the frequency responseof this amplifier by building the common collector a mplifier as shown in Figure 4. Configure the NIBode Analyzer with an input signal of amplitude 1 V and DC offset of 1 V (which is 2 V effective DCoffset) for vinand VBI AS.2. Repeat the above procedures on using the NI Bode Analyzer to find the frequency response of thisamplifier. Attach the Bode plot to the Lab Report. However, keep in mind that the breadboardhas a parasitic
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