TEE 208/05 Analog Electronics
Tutor-marked Assignment 2 (TMA 2 – 25%)
Evidence of plagiarism or collusion will be taken seriously and the University regulations will be applied fully. You are advised to be familiar with the University’s definitions of plagiarism and collusion.
Instructions:
This is an individual assignment. No duplication of work will be tolerated. Any plagiarism or collusion may result in disciplinary action, in addition to ZERO mark being awarded to all involved.
You are to submit online of your answers in OAS system and it is your responsibility to submit your TMA correctly and timely. OAS system does not allow re-submission of assignment. Marks will be awarded for correct working steps and answer.
The total marks for TMA 2 is 100 and contributes 25% towards the total grade.
TMA 2 covers the topics in Units 1, 2, 3 & 4.
You must submit your TMA 2 to OAS as one single document. Any additional appendices or attachments must be placed at the end of the submitted document and must be referred to in the main body of the assignment, or it will not be read by the marker.
Your assignment must be word processed (single spacing) and clearly lay out. Use the Insert-Equation function whenever you need to show equation or formula.
All files or documents submitted must be labeled with your WOU ID and name.
Answer all parts in English. All working steps and calculations must be shown clearly.
Question 1 (20 Marks)
[Note: Question 1 is to be done outside the lab hours]
Calculate the DC bias voltages (V_(c_1 ),V_(c_2 ),V_(E_2 ),V_(B_1 ),V_(CE_2 )) and currents (I_(B_1 ),I_(c_2 ),I_(E_2 )) for Darlington configuration in Figure 1. Given ß_1=60,ß_2=70.
Figure 1
Question 2 (20 Marks)
[Note: Question 2 is to be done outside the lab hours]
A JFET source follower amplifier circuit with voltage divider biasing is configured as shown in Figure 1a. The supply voltage VDD is 10V. The JFET has the following parameters which are: IDSS = 50mA and VP = –3.5V. The JFET is biased with VGS = 0V and VS = 0.5VDD. The small signal input impedance is 50k? and the value of the load resistor RL is 10k?.
Figure 2
Draw the small signal ac equivalent circuit of this amplifier.
Calculate the value of RS.
Calculate the values of R1 and R2.
Calculate the voltage gain of this amplifier. State your assumption where necessary.
Question 3 (20 Marks)
Lab 1-Zener Circuits and Applications
Theory:
Zener diode is designed to operate in reverse conduction. Zener breakdown occurs at a precisely defined voltage, allowing the diode to be used as a voltage reference or clipper. While Zener diodes are usually operated in reverse conduction, they may also be operated in cutoff and forward conduction. There are two different effects that are used in “Zener diodes”. The only practical difference is that the two types have temperature coefficients of opposite polarities.
Zener breakdown – Occurs for breakdown voltages greater than approximately 6V when the electric field across the diode junction pulls the electrons from the atomic valence band into the conduction band, causing a current to flow.
Impact ionization (also called avalanche breakdown) – Occurs at lower breakdown voltages when the reverse electric field across the p-n junction causes a cascading ionization, similar to an avalanche, that produces a large current.
Figure 3: I-V Curve of a typical Zener Diode
A reference diode is a special Zener diode designed to use both conduction modes, which cancels the temperature coefficients and produces a temperature stable breakdown voltage.
Zener diode ratings include:
Zener Voltage (Vz@Izt)
Power Dissipation (Pd)
Max Current (Izm)
Zener Impedance (Zzt)
Max Leakage Current (IR@VR)
Temperature Coefficient (aVZ)
The model for a reverse biased Zener diode (on the left side of the Figure 4) can be represented as a series circuit consisting of a regular diode with voltage drop Vf, a bias voltage source to provide a total drop of VZ across the Zener diode terminals, and a resistor to represent the Zener impedance (Rf represents the slope of the reverse conduction V-I curve). For this lab, we will neglect the effects of Rzt. The forward biased Zener diode would simply be a regular diode (on the right side of the Figure 4).
Figure 4: Zener Diode (left) and it's model (right)
Objectives:
In this lab exercise, you will build two clipper circuits – one use a 1N4001 diode and another uses 1N4732A zener diode. The characteristics of Zener diodes compare to diode will be compared in the clipper circuits you built.
Background:
When forward biased, a Zener diode is identical to a regular diode. When reverse biased, the Zener diode can be modeled as a regular diode connected backwards with a bias supply in series. The circuit of Figure 5 is the equivalent model for the Zener diode circuit of Figure 6.
Figure 5 :Diode clipper circuit
Figure 6: Zener diode clipper circuit
Instruments and components
1. 1N4001 diode – 1 pcs
2. 1N4732A diode – 1 pcs
3. 470 O – 1 pcs
4. 10k O – 1 pcs
5. Crocodile clip cable
6. DC Power supply
7. Oscilloscope with 2 probes with build-in function generator or
8. Oscilloscope with 2 probes with separate unit Function Generator
Procedures
1. By using 1N4001 diode, 470 O and 10k O resistor, construct a clipper circuit as shown in Figure 7.
2. Set your power supply to output 4.1 V that will be used as bias in this circuit.
3. Ensure your function generator is set to high impedance (or Hi-Z) output.
4. Set your function generator to generate RAMP waveform to output a -2.5 V to +2.5 V rise over 5 ms. Feed the waveform to the clipper circuit as Vi(t).
5. Connect channel 1 of the Oscilloscope to Vi(t) and channel 2 to the Vo(t).
6. Set the horizontal scale of the scope to 200 ms/div and vertical scale to 5 V/div.
7. Draw the waveforms displayed on the scope to your TMA.
8. Next, remove diode 1N4001 and the DC Power Supply. Replace it with 1N4732A as shown in Figure 8.
9. Under the same settings on the scope and function generator, draw the new waveform displayed on the scope to your TMA.
10. Overlay both waveforms in this lab into 1 single graph below.
Figure 7: Diode clipper circuit.
Figure 8: Zener Diode Clipper circuit
Questions:
1. Explain the working principle of clipper circuit.
[5 marks]
2. Draw the waveform you observed on the screen of the scope in step 9 and 11 above. Compare the waveform observed with the simulated results.
[5 marks]
3. From the waveform you observed, what is the output clipping voltages and Vi where the output waveform begins to clip?
[5 marks]
4. Explain the purpose of setting the DC Power Supply to 4.1 V in the diode clipper circuit?
[5 marks]
Appendix
1N4001 Data sheet – attached in a separate file.
1N4732A Data sheet – attached in a separate file.
Question 4: (40 Marks)
Lab 2 BJT and Cascaded Amplifier
Theory:
Bipolar Junction Transistor or simply BJT is a semiconductor device constructed with three doped regions with each region known as emitter, base and collector. These regions are form by doping p-n junctions „back-to-back?. Unlike Field Effect Transistor (FET), BJT is current driven amplifier with Ic = ßIB.
Figure 9: Diagram and schematic of PNP and NPN transistor
Objectives:
In this lab, we will construct a common-emitter amplifier circuit to examine BJT voltage gain, the characteristics of BJT active and the overall operation of a two-stage common-emitter amplifier. We will use 2N3904 NPN general purpose amplifier to build an amplifier circuit to analyze the performance.
Figure 10: Pin configuration of 2N3904.
Background:
One of the common applications of a BJT is amplify signal at its input. The amplified signal can feed into another stage to multiply the gain of the system. Both DC and AC analysis need to be carried out carefully to determine the performance of a multiple stages amplifier circuit.
BJT Equations Summary
Referring to the NPN transistor below, some of the commonly used equations are provided to assist you in the lab.
Figure 11: NPN representations for equation.
Instruments and components
1. 2N3904 NPN – 2 pcs
2. 150 O – 2 pcs
3. 1 kO – 2 pcs
4. 1.5 kO – 1 pcs
5. 2.2 kO – 2 pcs
6. 3.6 kO – 2 pcs
7. 10 kO – 2 pcs
8. 1 µF – 1 pcs
9. 10 µF – 2 pcs
10. 470 µF – 2 pcs
11. Crocodile clip cable
12. DC Power supply
13. Digital Multimeter
14. Oscilloscope with 2 probes with build-in function generator or
15. Oscilloscope with 2 probes with separate unit Function Generator
(Lab 2 Part A):
Procedures:
1. Construct the circuit shown in Figure 12 on a breadboard carefully.
2. Before connect the function generator to the circuit, perform DC analysis for the entire circuit and record your answers in the Table 1 below.
3. Next, connect the function generator to the circuit.
4. Set the function generator to output a sine wave at 1 kHz and amplitude equal to 5 Vp-p. Use a Oscilloscope to ensure the settings are correct (optional).
5. Turn on the output of the function generator and DC power supply. Measure and record all the DC and AC values in Table 1 and 2 below by using Multimeter.
6. Using the measured values of VB(Q1) and VC(Q1), calculate AV(Q1). Insert this value in the measured section of Table 2.
7. Using the measured values of VB(Q2) and VC(Q2), calculate AV(Q2). Insert this value in the measured section of Table 2.
8. Using the measured values of VB(Q1) and VC(Q2), calculate AVT. Insert this value in the measured section of Table 2.
Figure 12: A 2-satge common-emitter amplifier circuit
Questions
1. Perform DC analysis on circuit in this lab by filling up Table 1 below. Be sure to show all your steps and calculations.
Table 1: DC analysis values
[5 marks]
2. Perform AC analysis on the circuit in this lab by filling up table 2 below. Be sure to show all your steps and calculations.
Table 2: AC analysis values
[5 marks]
3. Determine the values of Zbase for Q2, Zin for Q2 and rc for stage 1. Calculate Av1.
[3 marks]
4. Determine the values of rc for stage 2. Calculate AV2.
[2 marks]
5. Calculate AVT. Compare the values of AVT measured vs AVT calculated and AVT simulated. Obtain the percentage error between these values. Explain discrepancy in the results between measured, simulated and calculated.
[5 marks]
(Lab 2 Part B):
Modify the circuit shown in Figure 12 by removing capacitors C4 and C5. Repeat the procedures in Part A and answer the questions as in Part A. [20 marks]
Appendix
2N3904 Data Sheet – attached in a separate file.
END OF TMA 2
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