Departement Elektriese, Elektroniese en Rekenaar-Ingenieurswese Finale Eksamen Kopiereg voorbehou Analoogelektronika ENE310 08 Junie 2010 Toetsinligting / Test information: Department of Electrical, Electronic and Computer Engineering Final Examination Copyright reserved Analogue Electronics ENE310 08 June 2010 Maksimum punte / Maximum marks: 100 Volpunte / Full marks: 100 Duur van vraestel: Duration of paper: 180 minute 180 minutes Eksamineringsbeplanning: n Addisionele 10 minute sal aan die begin van die eksaminering beskikbaar gestel word. Gedurende hierdie tydperk mag kandidate nie op die antwoordstelle skryf nie. Test planning: An additional 10 minutes will be availed at the start of the examination. During this period, candidates may not make any markings on the answer scripts. Oopboek / toeboek: Open / closed book: Oop (Enige materiaal) Open (Any material) Geen toestel met n kommunikasiepoort (van enige aard) word toegelaat nie. Any device with a communication port (of whatsoever kind) may not be used. BELANGRIK- IMPORTANT 1. Die eksamenregulasies van die Universiteit van Pretoria geld. The test & examination regulations of the University of Pretoria apply. 2. Vrae moet in onuitwisbare ink beantwoord word. Geen antwoorde wat in potlood geskryf is sal gemerk word nie. Questions must be answered in indelible ink. Answers in pencil will not be marked. 3. Beantwoord al die vrae en skryf u antwoorde in u Antwoordboek neer. Geen vrae mag op die vraestel beantwoord word nie. Answer all the questions and write the answers in the supplied Answer Book. No questions are to be answered on the Question Paper. 4. Toon alle berekeninge waar van toepassing. Geen punte sal toegeken word vir korrekte antwoorde sonder berekeninge om dit te staaf nie. Show all calculations where applicable. No marks will be given for correct answers without calculations/reasoning to support them. 5. Gebruik duidelik geregverdigde & kundige Ingenieursbenaderings (en/of aannames) waar/indien van toepassing. Use clearly justified & educated Engineering approximations (and/or stated assumptions) where/as appropriate. Dosent: Lecturer: Dr Saurabh Sinha ( ssinha@ieee.org) Eksterne Eksaminator: External examiner: Johan Schoeman ( johan.schoeman@eng.up.ac.za) Vertaler (Engels Afrikaans): Translator (English Afrikaans): Antonie Alberts ( ac.alberts@ieee.org) Beoordeelaar (Vraag 1) Evaluator (Question 1) Beoordeelaar (Vraag 2) Evaluator (Question 2) Beoordeelaar (Vraag 3) Evaluator (Question 3) Beoordeelaar (Vraag 4) Evaluator (Question 4) Beoordeelaar (Vraag 5) Evaluator (Question 5) Beoordeelaar (Vraag 6) Evaluator (Question 6) Meghan van Wouw ( meghanvanwouw@gmail.com) Christo Janse van Rensburg ( christojvr@ieee.org) Blessing Buthelezi ( blessing.buthelezi@gmail.com) Richard Balson ( richard.balson@gmail.com) Antonie Alberts ( ac.alberts@ieee.org) Johan Venter ( johan.venter@tuks.co.za) Groephoof: Ek bevestig dat die vraestel die uitkomstes toets soos gespesifiseer in die studiehandleiding. Group head: I confirm that the question paper evaluates the outcomes as specified in the study guide. Groephoof: Group Head (Acting): Dr Saurabh Sinha Handtekening: Signature: Totale aantal bladsye (hierdie blad ingesluit) / Total number of pages (including this page): 10
Study Theme Notional hours % (Exam) Question(s) 1: Introduction to amplifier circuits 18 11 1 2: Bipolar transistor amplifiers 26 15 5 3: Field effect transistor amplifiers 22 14 2 4: Differential and multistage amplifiers 10 6 3 5: Amplifier frequency response 34 21 2; 4 6: Feedback 30 19 5 7: Output stages and power amplifiers 22 14 6 162 100 % 100 marks AFRIKAANS AGTER OP 2
Question 1 [11] 1.1 Determine the output voltage, v O, of the 4 bit weighted resistor digital to analogue converter 1.1.1 [2] if the input signal is 0110, and 1.1.2 [2] if the input signal changes to 1001. For this problem, assume R F = 10 kω. v o 1.2 [4] The figure below shows a phototransistor that converts light intensity into an output current. The transistor must be biased as shown. The transistor output versus input characteristics are shown. Light intensity Design the current to voltage converter shown below (choose values for R F and V E ) to produce an output voltage between 0 and 8 V for an input light intensity between 0 and 20 mw/cm 2. Power supplies of ±10 V are available. v o V E AFRIKAANS AGTER OP 3
1.3.1 [2] The circuit shown below is an analogue voltmeter in which the meter reading is directly proportional to the input voltage, v I. Design the circuit (choose a value for R) such that a 1 ma fullscale reading corresponds to v I = 10 V. Resistance, R 2 corresponds to the meter resistance, and R 1 corresponds to the source resistance. v o 1.3.2 [1] Does the value of the source resistance, R 1, influence the design of the analogue voltmeter shown above? AFRIKAANS AGTER OP 4
Question 2 [25] Consider the amplifier shown below. V SS r in v o Power supplies: V DD = 3 V and V SS = 3 V V DD r out The PMOS transistor parameters: V TP = ½ V. K P = ½ μ p C ox (W/L) = 0.8 ma/v 2 and λ = 0.01 /V C gs = 2.5 pf C gd = 0.5 pf C ds = 0.1 pf The load resistor, R L = 2 kω. 2.1 [6] Design (choose values for R S and R D ) the circuit such that I D = ¼ ma and V SD = 1.5 V. Using appendix A, choose standard (5 %) resistors. 2.2 [3] Determine the small signal gain, A v = v o /v i. Express the gain in db. 2.3 Determine the values of the small signal resistances: 2.3.1 [1]r in 2.3.2 [2] r out 2.4 [1] Determine the total dc power delivered by the voltage sources, V SS and V DD. 2.5 [1] Determine the dc power dissipated by the transistor, P Q. 2.6 Assume C S = 47 µf and C C1 = C C2 = 10 µf 2.6.1 [3] Determine the high frequency cut off for the circuit, f H. 2.6.2 [4]Determine the low frequency cut off for the circuit, f L. 2.6.3 [4] Sketch the Bode magnitude and phase plot. AFRIKAANS AGTER OP 5
Question 3 [6] Consider the differential amplifier shown below. Transistor parameters are V TN = 0.8 V, K n = 0.4 ma/v 2, and λ = 0 Assume the transistors are matched. 3.1 [4] Design (choose R D ) the differential amplifier such that v O = v D1 v D2 = 1 V, when v 1 = 50 mv and v 2 = 50 mv. 3.2 [2] Determine the maximum common mode input voltage, v i,cm. AFRIKAANS AGTER OP 6
Question 4 [10] 4.1 [4] Design the active filter in the figure shown below such that the input resistance, r in is 20 kω, the low frequency gain is 15, and the 3 db frequency is 5 khz. Assume an ideal operational amplifier. r in v o 4.2 [6] Sketch the Bode magnitude and phase plot. AFRIKAANS AGTER OP 7
Question 5 [34] 5.1 Consider the series shunt feedback circuit below. r o,fb r i,fb v o Transistor parameters: h fe = 120, V BE(on) = 0.7 V and V A 5.1.1 [9] Determine the dc operating currents (I C ) for the three transistors Q 1, Q 2, and Q 3. 5.1.2 [6] Determine the ac small signal parameters (r π and g m ) for the three transistors Q 1, Q 2, and Q 3. 5.1.3 [4] Determine the open loop gain, A vo. 5.1.4 [3] Determine the feedback factor, β. 5.1.5 [1] Determine the amount of feedback, 1 + A vo β. 5.1.6 [2] Determine the closed loop small signal voltage gain, A vfb = v o /v i. 5.1.7 [2] Determine the input resistance of the closed loop feedback configuration, r i,fb. 5.1.8 [2] Determine the output resistance of the closed loop feedback configuration, r o,fb. 5.2 [5] A feedback amplifier has a low frequency open loop gain of 4000 and three poles, f P1 = 400 khz, f P2 = 4 MHz and f P3 = 40 MHz. A dominant pole is to be inserted such that the phase margin is 60. Assuming the original poles remain fixed, determine the dominant pole frequency. AFRIKAANS AGTER OP 8
Question 6 [14] 6.1 Consider the ideal class B output stage shown below. v o The output stage is to deliver 50 W of average power to a 24 Ω load for a symmetrical input sine wave. Assume the supply voltages for ±n volts, where n is an integer. 6.1.1 [3] The power supply voltages are to be at least 3 V greater than the maximum output voltage. Determine the power supply voltages. 6.1.2 [2] Determine the peak current in each device. 6.1.3 [2] Determine the efficiency of the amplifier. 6.2 A particular transistor is rated for a maximum power dissipation of 60 W if the case temperature is 25 C. Above 25 C, the allowed power dissipation is reduced by 0.5 W/ C. 6.2.1 [3] Sketch the power derating curve. 6.2.2 [2] Determine the maximum allowed junction temperature. 6.2.3 [2] Determine the thermal resistance, Θ dev air (in C/W). AFRIKAANS AGTER OP 9
Appendix A AFRIKAANS AGTER OP 10
Studentenommer / Student Number Volle Voorname / Full Name QUESTION/VRAAG 1 v o/u 1.1.1 [2] 1.1.2 [2] Beoordelaar 1 (Vraag 1) Evaluator 1 (Question 1) Meghan van Wouw ( meghanvanwouw@gmail.com)
1.2 v o V E [4] 1.3.1 [2] 1.3.2 [1] Beoordelaar 1 (Vraag 1) Evaluator 1 (Question 1) Meghan van Wouw ( meghanvanwouw@gmail.com) Total/Totaal: [11]
Studentenommer / Student Number Volle Voorname / Full Name QUESTION/VRAAG 2 r in r out 2.1 [6] Beoordelaar 2 (Vraag 2) Evaluator 2 (Question 2) Christo Janse van Rensburg ( christojvr@ieee.org)
2.2 [3] 2.3.1 [1] 2.3.2 [2] 2.4 [1] Beoordelaar 2 (Vraag 2) Evaluator 2 (Question 2) Christo Janse van Rensburg ( christojvr@ieee.org)
Studentenommer / Student Number Volle Voorname / Full Name 2.5 [1] 2.6.1 [3] 2.6.2 [4] Beoordelaar 2 (Vraag 2) Evaluator 2 (Question 2) Christo Janse van Rensburg ( christojvr@ieee.org)
2.6.3 Ajω ( ) db f L f H f [Hz] [2] A( jω) f L f H f [Hz] [2] Beoordelaar 2 (Vraag 2) Evaluator 2 (Question 2) Christo Janse van Rensburg ( christojvr@ieee.org) Total/Totaal: [25]
Studentenommer / Student Number Volle Voorname / Full Name QUESTION/VRAAG 3 3.1 [4] Beoordelaar 3 (Vraag 3) Evaluator 3 (Question 3) Blessing Buthelezi ( Blessing.Buthelezi@gmail.com)
3.2 [2] Beoordelaar 3 (Vraag 3) Evaluator 3 (Question 3) Blessing Buthelezi ( Blessing.Buthelezi@gmail.com) Total/Totaal: [6]
Studentenommer / Student Number Volle Voorname / Full Name QUESTION/VRAAG 4 r in v o 4.1 [4] Beoordelaar 4 (Vraag 4) Evaluator 4 (Question 4) Richard Balson ( Richard.Balson@gmail.com)
4.2 Ajω ( ) db f L f H f [Hz] [3] A( jω) f L f H f [Hz] [3] Beoordelaar 4 (Vraag 4) Evaluator 4 (Question 4) Richard Balson ( Richard.Balson@gmail.com) Total/Totaal: [10]
Studentenommer / Student Number Volle Voorname / Full Name QUESTION/VRAAG 5 r o,fb r i,fb v o 5.1.1 Beoordelaar 5 (Vraag 5) Evaluator 5 (Question 5) Antonie Alberts ( AC.Alberts@ieee.org)
[9] Beoordelaar 5 (Vraag 5) Evaluator 5 (Question 5) Antonie Alberts ( AC.Alberts@ieee.org)
Studentenommer / Student Number Volle Voorname / Full Name 5.1.2 [6] Beoordelaar 5 (Vraag 5) Evaluator 5 (Question 5) Antonie Alberts ( AC.Alberts@ieee.org)
5.1.3 [4] 5.1.4 [3] Beoordelaar 5 (Vraag 5) Evaluator 5 (Question 5) Antonie Alberts ( AC.Alberts@ieee.org)
Studentenommer / Student Number Volle Voorname / Full Name 5.1.5 [1] 5.1.6 [2] 5.1.7 [2] 5.1.8 [2] Beoordelaar 5 (Vraag 5) Evaluator 5 (Question 5) Antonie Alberts ( AC.Alberts@ieee.org)
5.2 [5] Beoordelaar 5 (Vraag 5) Evaluator 5 (Question 5) Antonie Alberts ( AC.Alberts@ieee.org) Total/Totaal: [34]
Studentenommer / Student Number Volle Voorname / Full Name QUESTION/VRAAG 6 v o/u 6.1.1 [3] Beoordelaar 6 (Vraag 6) Evaluator 6 (Question 6) Johan Venter ( johan.venter@tuks.co.za)
6.1.2 [2] 6.1.3 [2] Beoordelaar 6 (Vraag 6) Evaluator 6 (Question 6) Johan Venter ( johan.venter@tuks.co.za)
Studentenommer / Student Number Volle Voorname / Full Name 6.2.1 [3] 6.2.2 [2] Beoordelaar 6 (Vraag 6) Evaluator 6 (Question 6) Johan Venter ( johan.venter@tuks.co.za)
6.2.3 [2] Beoordelaar 6 (Vraag 6) Evaluator 6 (Question 6) Johan Venter ( johan.venter@tuks.co.za) Total/Totaal: [14]