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Department of Electrical Engineering and Electronics ELEC104 Experiment G: After-lab assignment Assessment Task You are required to answer a set of questions based on your work in Experiment G. Your assignment must be submitted electronically using the link on the Canvas site for the module. The document should be in PDF format. • Your work should be presented in a professional style, prepared in a word processor and containing neat diagrams and graphs. Your assignment should contain answers to the questions given below. Your answers must be based on the work that you carried out in the timetabled lab session. • Your report will be marked on the correctness of your answers and the clarity of any graphs/figures. Your answers must be based on the work that you carried out in the timetabled lab session. Questions from Part 1 (20 marks): 1.1 Insert a table containing your measurements of the input characteristic. 1.2 Insert a graph of your measurements, showing the dependence of IB on VBE. 1.3 From your understanding of transistors, briefly explain the shape of the curve that you observe in the graph from Q1.2. 1.4 Briefly explain the effect of changing the value of the resistor R₁ in the circuit shown in Figure 1.2. Explain why you think we have chosen a relatively large resistance value for this component? Questions from Part 2 (20 marks): 2.1 Insert a table containing your measurements of the output characteristic for the first case that you measured, the case of IB = 20 μА. 2.2 Insert a graph showing the dependence of Ic on VCE for all 3 cases of IB 2.3 From your understanding of transistors, briefly explain the shape of the curves that you observe in the graph from Q2.2. 2.4 Briefly explain the effect of changing the value of the resistor R₂ in the circuit shown in Figure 1.2. Explain why you think we have chosen a relatively small resistance value for this component? Questions from Part 3 (20 marks): 3.1 Insert a sketch or photo of the oscilloscope display showing Vout, the output from your amplifier. 3.2 From your measurements, what was the amplification of the circuit that you tested? Briefly explain how you determined this value. 1 Questions from Part 4 (40 marks): 4.1 What is the value of hie for the transistor used in your experiment. Show your calculation. 4.2 What is the value of hfe for the transistor used in your experiment. Show your calculation. 4.3 What are the four resistor values that you determined in this section. Show your calculation. For Part 4, you can upload an image of hand-written notes, but the notes must be clear and easy to understand. Experiment G Specifications Module(s) ELEC104 Component Experiment G: Transistors and Amplifiers Coursework weight 10% of your ELEC104 grade Level 4 Lab location EEE building, 3rd floor electronics laboratory Work Suggested study time Individual 6 hours laboratory + 6 hours after-laboratory work Assessment method Lab notes (pass/fail) + Assignment (100%) Submission link ELEC104 Canvas site 2/n Experiment G Department of Electrical Engineering and Electronics ELEC104 Experiment G: Transistors and Amplifiers Overview: The overall aim of this experiment is to give you the opportunity to learn about practical aspects of transistors and operational amplifiers. The experiment has several different parts. • Part 1, in which you set up a circuit to measure the input characteristic of an NPN transistor • Part 2, in which you use the same circuit to measure the output characteristics of the same transistor. • • Part 3, in which you build a common-emitter amplifier using the transistor that you have just tested. Part 4, in which you analyse the results of your measurements. While the transistors that you use are based on the same basic science, the specific properties depend on the semiconductor materials, transistor design and component tolerance. In this part, you are required to carry out analysis to find the properties of your transistor, and then design a new amplifier circuit based on that transistor. Assessment: The assessment is in two parts. Both documents should be uploaded to the ELEC104 Canvas site using the provided links for each one. • • Laboratory notebook (Pass/Fail) After your laboratory session, you should scan the relevant pages of your lab book, including any graphs, put them in a single document, and submit online in Word or pdf format by 11:59 pm on the day of your lab session. Your submission will not be given a mark, but you must submit your lab notes as evidence that you have done the work. Experiment G assignment (100%): You need to submit a short assignment on the experiment. This assignment is given on the ELEC104 Canvas site, in the section about Experiment G. You should write your assignment using a word processor and submit it online in pdf format. YOU MUST SUBMIT YOUR LAB NOTES TO PASS THE EXPERIMENT. YOUR REPORT WILL NOT BE MARKED UNLESS YOUR LAB NOTES WERE SUBMITTED ON THE DAY OF YOUR LAB SESSION. 1 Experiment G specifications: Module(s) Component Coursework weight Level Experiment G ELEC104 Experiment G: Transistors and Amplifiers 10% of your ELEC104 grade 4 Lab location Work Suggested study time Assessment method EEE building, 3rd floor electronics laboratory Individual 6 hours laboratory +4 hours after-laboratory work Lab notes (pass/fail) + Report (100%) Submission link ELEC104 Canvas site 2 Experiment G Part 0: The transistor for your experiment You have been allocated a transistor for your experiment. The laboratory has several different types of NPN transistors. They will all function similarly in a circuit but have different characteristics depending on the materials and physical dimensions of the transistor elements inside the component. You have been given a transistor according to your bench location, and you must use the same transistor for all parts of Experiment G. If you break the legs of the component, or think that it is faulty, you should check with a demonstrator or staff member. They will bring you a replacement of the same type. There are 8 different transistors, mounted in slightly differently packages. The identifying colour and the physical arrangement for the collector, base and emitter inputs for each type is shown in the table and figure below. You must record the transistor number in your lab notes, and state it in your assignment. Transistor ID 1 Identifying colour Mounting arrangement red Figure 1(a) 2 blue Figure 1(a) Table 1: transistors IDs 3 orange Figure 1(a) for the 8 types of NPN transistors used in Experiment G. 4 green Figure 1(a) 5 yellow Figure 1(a) 6 red Figure 1(b) white Figure 1(b) 8 black Figure 1(a) PINNING PIN DESCRIPTION 1 emitter 2 base 3 collector, connected to case C - Collector B - Base E - Emitter === MAM317 2 Fig.1 Simplified outline (TO-39) and symbol. (a) CBE (b) Figure 1: Pin arrangements for the two types of transistors used in Experiment G 3 Experiment G Part 1: Investigating transistor input characteristics 1.1: Background Figure 1.1 shows a typical input characteristic for a small-signal general purpose NPN transistor operating in the common-emitter mode. The input characteristic shows the relationship between current flowing through the transistor on the voltage between the base and emitter connections, and hence the graph in Figure 1.1 shows base current I plotted against base-emitter voltage VBE. From the graph, you can see that the base current is extremely small until the base-emitter voltage is about 0.6 V, then the current increases rapidly. This behaviour is very similar to the characteristic of a forward-biased silicon diode. 100 Figure 1.1: Current-voltage characteristic of an NPN transistor operated in the common-emitter mode. The plot shows the voltage between the base and emitter of the transistor VBE on the horizontal axis and the base current l on the vertical axis. This curve is called the input characteristic of the transistor. 80 80 60 60 40 40 20 20 Base current, (µА) 0 0 0.2 0.4 0.6 0.8 Base-emitter voltage VBE (volts) 1.2: Measuring the input characteristic of an NPN transistor Figure 1.2 shows a circuit that can be used to test the characteristics of a transistor. It has two DC power supplies. The VB supply on the left of the circuit diagram provides voltage and current to the base connector of the transistor. The Vc supply on the right of the circuit diagram provides voltage and current to the collector connector. In this activity, you will measure the input characteristic by measuring the current lÅ that flows into the transistor, while changing the value of the voltage VB. The voltage on the collector side of the circuit will remain constant. The first step is to set up the circuit so that you can make the appropriate measurements. Follow the steps below to make a first measurement. Set up the circuit in Figure 1.2 on your test board, using resistor values R1 = 180 k2 and R2 = 560 . • Set up the multimeter to measure VBE, the voltage between the base and emitter of the transistor. • For this first test measurement, set the two power supplies to be VB = Vc = 5 V. • Record the voltage VBE., This is the voltage between the base connection of the transistor and the ground in your circuit. 4 R1 www IB C Base_supply VB Q1 B E Experiment G R2 w Collector_supply Vc Figure 1.2: Circuit to measure the current-voltage characteristic of a transistor in the common emitter configuration . You also need to measure the current IB. To do this, you could set the multimeter in the circuit to measure the current. However, you should be able to work out the current from your voltage measurement by noting that the voltage across resistor R1 is given VR1 = VB - VBE. Then you can calculate IB = VR1/R1. • Record this value of IB. Do you understand the two methods of measuring currents mentioned above? If you are not sure, you should ask a demonstrator for an explanation. The steps above allowed you to measure VBE and lÅ for a single value of the supply voltage VB. To measure the input characteristic of the transistor, you need to measure the base current IB, as a function of the base- emitter voltage VBE. To do this, you should repeat the measurement that you just made, while changing the value of VB. • • Vary the value of VB and record the values of VBE and IB. You should change VB from 0 to 15 V in steps of 1 V. Figure 1.3 shows the type of table you could use to record your results. You are expecting to see something like the graph shown in Figure 1.1, so do not be surprised if IB is extremely low for low values of VB. In your lab notebook, draw a rough graph with VBE on the horizontal axis and I on the vertical axis. This is the input characteristic of the transistor. Your results should look something like the graph shown in Figure 1.1, with IB being very low for small values of VBE and then changing rapidly for voltage above 0.6 V. If your graph does not look similar to the example in Figure 1.1, check your method, or ask a demonstrator. 5