ObjectiveMaterialsProcedureCascode AmplifierCommon Emitter-Common Collector Multi-stage AmpliferUNIVERSITY OF CALIFORNIA AT BERKELEYCollege of EngineeringDepartment of Electrical Engineering and Computer SciencesEE105 Lab Exp er imentsExperiment 8: Multi-stage Amplifiers1 ObjectiveOften, a single stage transistor amplifier may not provide enough gain or input/output impedance for adesired application. To remedy this, we can c ascade amplifier sta ges to form a multi-stage amplifier withthe desirable gain or impeda nce properties. In this lab, we will examine the ca scode amplifier and anothermulti-stage amplifier formed by cascading a common-emitter and commo n-collector amplifier.2 MaterialsComponent Quantity2N4401 NPN BJT 42N4403 PNP BJT 251 kΩ res istor 220 kΩ res istor 1100 Ω r e sistor 251 Ω resis tor 110 kΩ potentiometer 110 µF capacitor 1100 µF capacitor 1Table 1: Components used in this lab3 Procedure3.1 Cascode Amplifier1. Construct the cascode amplifier (Q1and Q2) with current mirror bias (Q3and Q4) as shown in Figure1(a). Use two 51 kΩ resistor in parallel to make a 25 .5 kΩ resistor for RREFand a 51 Ω resistor forRS. Set VBI AS2to 1.5 V.2. Use the function generator to generate a 1 kHz, 20 mV peak-to-peak sinusoidal signal with a DC offsetof around 580 mV to 650 mV (you may have to adjust the offset after connecting the sig nal to theamplifier to ensure you get a clean output signal). Use this signal as vIN.3. Measure IBI ASand the DC voltage at vOU T.4. Using the oscilloscope , plot both the input vINand the output vOU T. Sketch the waveforms youobserve.5. Why is vOU Tnot sinusoidal?6. What is the peak-to-peak voltage of the output waveform? What are the gain and phase of vOU T/vIN?13 PROCEDURE 2−vIN+RSQ1Q2−+VBI AS2Q3Q4VCC= 12 VvOU TRREFIBI AS(a)−vIN+RSQ1Q2−+VBI AS2Q3Q4VCC= 12 VvOU TCRL+vL−RREFIBI AS(b)Figure 1:(a) Cascode amplifier test setup (b) Cascode amplifier test setup with load resis tance7. Now add a 10 µF capacitor to the node vOU Tand a 20 kΩ resistor from the capacitor to ground asshown in Figure 1(b). This resistor will act as a loa d to the amplifier.8. What is the peak-to-p e ak voltage of the output waveform (at vL) with the load resistor? What is thegain of the amplifier with the resistive load?9. Estimate the output res istance of this amplifier using the peak-to-peak voltages measured.3.2 Common Emitter-Common Collector Multi-stage AmpliferFrom the previous lab exercises, you tried using a spea ker as a load to a common emitter amplifier. However,the common emitter amplifier delivers very little voltage gain to the speaker because of the huge impeda ncemismatch between the a mplifier and speaker. In this se c tion of the lab, you will cascade a low outputimpeda nce common co llec tor amplifier to the output of a common emitter amplifier as a voltage buffer todrive a low impedance speaker.1. Before you begin, use the function generator to apply a sinusoidal signal with peak-to-peak voltage of40 mV and a frequency of 1 kHz dir e c tly to the sp e aker. Can you hear anything?2. Construct the c ascaded amplifiers as shown in Figur e 2. Set the potentiometer to around 8 kΩ forRC. For the rest of the circuit, let RS= 51 Ω, RREF= 200 Ω (use two 100 Ω resistors in series), andC = 100 µF.3. Use the function genera tor to generate a 40 mV peak-to -p e ak, 1 kHz frequency sine wave with a DCoffset of around 540 mV to 600 mV. Use this signal as vIN. Now, try to maximize the gain of theamplifier by incr easing the resistance of the potentiometer for RC. Can you hear a nything now? Feelfree to try out o ther frequencies to observe how the speaker responds to vario us frequencies.4. Measure IBI AS1, IBI AS2, and the DC voltages at vOU T 1and vOU T 2?5. Measure VBEof Q2. Is the DC voltage at vOU T 1enough to bias Q2in the forward active region?6. Using the oscilloscope, plot both the input vINand the output vOU T 2. Sketch these waveforms.3 PROCEDURE 3−vIN+RSQ1RCIBI AS1vOU T 1Q2VCC= 5 VCvOU T 2Q3Q4RREFIBI AS2Figure 2: Multi-stage amplifier test setup7. Measure the gain and phase of vOU T 2/vIN.8. Now increase the DC offset of the input waveform to 62 0 mV . What happens to the waveform atvOU T
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