BJT Fundamentals and Applications JOR

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1 Purpose: BJT Fundamentals and Applications JOR The purpose of this assignment is to design a Pulse Amplifier and a Common-Emitter Amplifier with voltage divider bias using a 2N2222A NPN bipolar junction transistor(bjt). This serves as a homework assignment and final laboratory assignment as a unit. Once you have designed each part use Multisim as your Lab test to verify DC Q- Point voltages and all appropriate input out put waveforms. Pulse Amplifier: In this section you will be designing a Pulse amplifier to convert a to 5 volt pulse to a to 12 volt pulse. In order to complete the design and construct the circuit in Figure 1, you will need to calculate the necessary component values. In any practical design one needs to know the interface requirements in order to design the circuit that connects the two interfaces together. In the case of Pulse Amplifier, those requirements are as follows: Design a Pulse Amplifier that is driven from a source that is capable of driving 5 volts into 5 ohms and the output should be capable of delivering 12 ma when the collector-emitter is shorted. The supply voltage is 12 volts and the initial source frequency is 1 Khz. A typical circuit for this is shown in Figure Khz 5 V Pulse XFG1 + C1 }1UF - Note, a 5 volt Pulse Lf 'P goes from Ovto 5v. Vs 4 V1 -=-12 V ~ Cbe=25pf Vb 3 A R1 Vc ;----= ' 2 1 U1 -: 2N2222A* XSC1 B ExtTri ~3 o C4 Figure 1

2 1. In Multisim, connect a 2N2222 transistor to the Curve Tracer and obtain the output characteristic curves. Use the grapher to obtain the curves and adjust the curve so its origin is at zero and chose appropriate scales. The make a paper copy of the output characteristics so that you can use it to design your circuit( draw load-line, etc.). 2. Use the above characteristics and draw a load-line from the given design criteria and determine the Saturation point. What is the value of the base current that just brings the transistor in saturation? Use this to calculate the base resistor R2. R1 is obtained from the given output requirement. 3. Set-up the circuit in Figure 1 with the component values you obtained. Using a 5 volt pulse at 1Khz as an input, obtain and record the input/output waveforms. Does the output go to zero like the input pulse when it is in it's lowest state? Explain. 4. Assume a base current overdrive factor of 1.5 and re-calculate R2. Insert this new value of R2 into your circuit and do part 3 above, again. 5. Adjust the frequency of the generator to 4Khz and record the input/output waveforms. Explain. 6. Now connect a loopf capacitor C3(speed up cap) across R2 and record the input/ output waveforms. Explain. 7. Now connect a loopf capacitor C4 across the output to simulate wiring and device loading capacitance. Record the input/output waveforms and explain. 8. Do you know why I put O.Olufin parallel with a 1uf across the supply? Common-Emitter Amplifier with voltage divider bias: In this section of the laboratory you will be designing a commonemitter amplifier using the most stable bias configuration. This configuration is shown in Figure 2. Before the circuit can be setup, a set of design criteria must be obtained so appropriate component values can be calculated and inserted into the circuit. Design a CE amplifier to amplify a 4mv pp, sine wave signal, to 1 volt pp, into a 1 k ohm load. The available power supply is 12 volts. In your design, use the "rule of thumb" that Ve:::::.1 Vcc and that the bias network current 14 = 1 Ib to minimize the BJT loading on the R1, R4 input bias network. This effectively says that the resistor R4 is 1/1ththe BJT input resistance. It is also desired that Vce be Y:! Vcc which is generally a good starting point unless there are other criteria that need to be met. This generally yields a low distortion peak to peak output voltage swing provided the output swing is less than 1/4thof the power supply.. 1. First, calculate the collector resistor R2 utilizing the maximum power transfer theorem. Using the rule of thumb for Ve, calculate the collector quiescent operating voltage and then the emitter resistor, R3. 2. Draw the load-line on the output characteristic curve, noting the location of the Q- point based on the Vce criteria. 3. Record the Q-Point collect current, voltage and resulting base current. From this calculate the current gain beta and the approximate transistors input resistance Rin. 4. Calculate II, 14, Rl and R4. Now that all the resistor values have been determined, construct the circuit in Figure 2.

3 3 VCC C5 IOnF XSCl Ay A ExtTri R1 R2 8 Vcout C2 4 Vc + - U1 Vin C1 Vbq 5 + 2N2222A* 1uF R4 Veq R3 C3 33uF Figure 2 5. With the output load resistor R5 and the signal generator disconnected, measure Vcq, Vbq, veq and the supply voltage. Note, before you use the AFG321 generator make sure you have put a 5 ohm load resistor across its output otherwise the signal coming out of the generator will be larger than what you set on its screen. It is not shown in Figure 1 so as not to make the experiment equipment dependent. 6. Connect the signal generator and record Vcq and Vin on the oscilloscope using DC coupling on both channels. Move the scope probe from Vcq to Vout and record these signals. Now connect the output load resistor R5 and record the resulting waveforms. Do these waveforms make sense? Explain. 7. Using the input/output waveforms with R5 connected, calculate the voltage gain Av = Vout / Vin. 8. Using the simulator only, do an AC Analysis(frequency response) and Fourier Analysis on the output node. Explain the significance of these plots. 9. Remove the emitter capacitor C3 and calculate Av for the new output voltage. 1. Insert a 22uffor the emitter capacitor C3 and record the input/output waveforms. Calculate the Av and explain any other noticeable differences in the input/output waveforms in comparison to those when C3 was 33uf..

4 11. Increase RI to approximately 3 times your calculated value and record Vin and Vout. Oscilloscope channels should still be on DC coupling. Now decrease RI too approximately to 113your calculated value and record these waveforms. Explain. 12. Re-install your calculated value for R1. From your measurements you should have measured a peak: to peak: output greater than 1. volt pp. If it is desired to have the output approximately 1. volt pp without changing the other interface requirements, how could you do it with one resistor at the input? Chose a resistor to meet this requirement and insert it in your circuit and verify it works. Record the input/output waveforms. If the original output signal was a little distorted, did this change have any effect? Explain.

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Experiment #8: Designing and Measuring a Common-Collector Amplifier

SCHOOL OF ENGINEERING AND APPLIED SCIENCE DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING ECE 2115: ENGINEERING ELECTRONICS LABORATORY Experiment #8: Designing and Measuring a Common-Collector Amplifier