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 110 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 Amplifier−+VBIAS−vin+RSVCC= 5 VRCIBIASvOU TFigure 1: Common emitter amplifier test setup13 PROCEDURE 21. Construct the common emitter amplifier as shown in Figure 1 . Use a RC= 10 kΩ and RS= 51 Ω.2. Use a function generator to generate a 25 mV peak-to-peak, 1 kHz sinusoidal signal with a DC offset o f580 mV. This signal is both VBIASand vincombined, and will be referred to as vIN. Note: You m aynotice some nonlinear effects on the output waveform. This is due to the high input signal amplitudethat we are using. We choose this amplitude to avoid noise from the oscilloscope messing up our Bodeplot measurements in a later step.3. What is IBIASand 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 are the magnitude and phas e of vout/vinmeasured from the oscilloscope?6. Instead of using the oscilloscop e to measure the magnitude and phase of vout/vinat other frequenciesmanually, let’s use NI Bode Analyzer software to automate the proces s. To avoid errors from thesoftware, make sure you follow the instructions below to set up the software:• Make sure that vINis on Channel 2 and vOU Tis on Channel 1.• Connect the Trigger Output fr om the function generator to the Exter nal Trigger port of theoscilloscope.• Open NI Bode Analyzer.exe from the computer desktop.• When both the function generator a nd the oscilloscope ar e 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 stop frequency to 2 MHz for this measurement. You can leave the starting frequency atits 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 290 mV because the function generator outputs an offset that is twice as large as t hevalue entered here.• Hit “Run”! The software will start sweeping the input across different frequencies to generate aBode plot.7. After the software is done producing the Bode plot, you can drag the curs or on the plot to read outthe magnitude and phase at different frequencies . Drag the cursor to around 1 kHz. What are themagnitude 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 from its DC value by 3 dB. This is thedominant pole of the amplifier. What is the pole frequency? What is the phase at this frequency? Isthe phase consistent with the magnitude? (Recall that at the −3 dB point, the phase should be dropfrom its DC value by 45 degr e e s.)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 a .csv (which can be o pened in Microso ft Excel) file by clicking the“Export” button. Print the plot out and turn it in with your Lab Report. You do not have to find thesecond pole beca us e it occurs at a frequency higher than what is measureable by our equipment.3 PROCEDURE 3−+VBIAS−vin+RSCMVCC= 5 VRCIBIASvOU TFigure 2: Miller capacitor test setup3.2 Miller Effect1. The Miller effect can be best examined by introducing a Miller capacitor across the amplifier. Let’stake a look at the impact of the 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 stop frequency to 500 kHz. Attach the Bode plot to the Lab Report.3. How does the dominant po le of this amplifier compare to the dominant pole of the prev ious amplifier?Is this expected?4. In this amplifier, we are using a 1 nF capacitor to simulate a la rge base-collector capacitor (Cµ). If weare to des ign an amplifier with high bandwidth, is a transistor with a large Cµdesirable?3.3 Output Capacitance1. Let’s examine the impact of output capacitance on a common emitter amplifier. Take out the Millercapacitor CMfrom Section 4.2 and place it at the output as shown in Figure 3.−+VBIAS−vin+RSVCC= 5 VRCIBIASvOU TCMFigure 3: Output capacitance test setup2. Repeat the above procedures on using the NI Bode Analyzer to find the frequency response of thisamplifier, but set the stop frequency to 500 kHz. Attach the Bode plot to the Lab Report.3 PROCEDURE 43. How does the dominant po le of this amplifier compare to the dominant poles of the previous twoamplifiers? I s this expe c ted?3.4 Common Collector Amplifier−+VBIAS−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 VBIAS.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 bre adboard hasa parasitic capacitance that will start deforming the signal when
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