EE 321 Lab 13 Fall 2003EE321 – Lab 13Bipolar Junction Transistors, Part IV AM Radio ReceiverIn this lab you will work in teams to construct and test three modules, then connect themtogether to make a radio receiver that will pick up an AM radio station. The three modules area radio frequency (RF) amplifier, an amplitude modulation detector and a power amplifier. Oneteam member should build and test the Push-pull amplifier and AM detector. At the same timethe other team member should build and test the RF amplifier. Both team members should worktogether to make measurements showing that each module works correctly.Since this lab will be complex be very neat. Building the RF amplifier on a separate breadboardwill reduce feedback through ground lines.A. Push-Pull Amplifier.1. The emitter follower circuits of Lab 8 can supply bipolar currents to a load, but the negativeload current is restricted in m agnitude to the value of the bias emitter current. For largeoutput currents, this means that the power dissipated in the transistor is large when nosignal is present. The transistor dissipation is reduced by using the ‘push-pull’ configurationshown in Figure 1. Construct the push-pull circuit and sketch its response to a 1 kHz sinewave. Do this on the right side of your proto board to allow room for more circuitry later.Sketch the output waveform. What causes the ‘cross-over’ distortion?VoutTIP32VinTIP311K+15V−15VFigure 1.2. The cross-over distortion can be reduced by including it inside the feedback loop of the opamp. Build the circuit of Figure 2 and observe Voutfor a sine wave input. What has happenedto the cross-over distortion, and why? (Hint: look at the output of the op amp itself.)WARNING If there is any error in this circuit the output transistors can over heat. Check tobe sure they don’t get hot. Ground the input and make sure that the output is almost 0 V.3. Reduce the output amplitude to 1 V rms at the frequency three octaves above middle ‘C’(f = 440 Hz). Make certain there is no DC offset on the output before connecting it to thespeaker. Connect the 8 Ohm speaker to the output. (Before doing this, compute the power1EE 321 Lab 13 Fall 2003VoutVinTIP32TIP311K+15V−15V10K390100KLF411Figure 2.that will be applied to the speaker. Will this produce a loud, medium, or soft tone?) Trysine, square and triangular wave inputs. Why do they sound different?4. Measure the audible frequency response of this ‘hi-fi’ system. What is the frequency responselimited by?B. AM Detector5. The detector is basically a peak detector and high pass filter. Build the circuit shown inFigure 3. Set the input to a 1 MHz, 4 V p-p sine wave with a 1 V offset. Observe the signalat point B. Change the input amplitude by a volt and me asure the change at point B. Tryother amplitudes, frequencies and offsets, and determine what the circuit is doing.LF411LF411Vin10K10K10K10K0.15uF1N4148VoutABC0.015uFFigure 3.6. Reduce the input frequency to 1 kHz 1 V p-p sine wave with a 2 V offset. The output at Cshould be a sine. Why? Low frequencies should be blocked by the 0.15 µF capacitor. Findthis cutoff frequency, fc.2EE 321 Lab 13 Fall 2003C. RF AmplifierThe amplifier in Figure 4 uses a ‘casco de’ configuration (Q1, Q2) to reduce the effect of the(Miller) capacitance across the base-collector junction of Q2. This improves the high frequencyperformance of the amplifier circuit. (See the discussion on pages 622 to 626 of the text.) Anemitter follower Q3provides the circuit with a low output impedance. Use 2N2222 transistors forthis circuit, which have better high frequency capability than 2N3904’s.inVVout+15V−15V2.7K8.2K3.9K18K2.7K3.9K2uF0.1uFQ1Q2Q3Q1, Q2, Q3: 2N22220.1uF0.01uF470Figure 4.7. Construct the c ircuit neatly on your proto board. Measure the DC bias voltages to make surethat all transistors are in their active state. Checking bias voltages is a very useful way todetect bad wiring or bad components.8. Input a small signal and measure the gain at 1 MHz. Measure the frequency response (findthe 3 dB frequencies).D. A Simple AM Radio9. Test the operation of the c ircuit by using your body as an antenna. You should have about1 V p-p output signal, whose amplitude appears to be ‘noisy’. Measure the frequency (near1 MHz). Sketch the shape of the amplitude-modulated wave form (between 100 Hz and 1 kHz ).10. Connect the RF amplifier to the detector. Look at the detected signal on your scope. Makesure there is no DC offset. Connect this to the power amplifier and to the speaker. Listen towhat the mysterious waveform sounds like.3EE 321 Lab 13 Fall 2003Pre-Lab1. Find the output voltage and the power dissipated by the transistors and the load for thecircuit of Figure 1 for the following input voltages: 2 V, 1 V, 0.5 V, 0 V, -0.5 V, -1 V,-2 V. Assume the base-emitter voltage drop is 0.7 V when the transistor is in the active orsaturation mode, and that β = 100.2. Find the bias voltages and currents in Figure 4. Assume that VBE= 0.7 V when the transis-tors are in the active or saturation mode, and that β = ∞.3. In Figure 4, Q1, Q2and Q3are all being used in one of the standard amplifier configurations— common emitter, common base, or emitter follower.(a) What configuration is Q1?(b) What configuration is Q2?(c) What configuration is Q3?(d) What is the input voltage to the amplifier of