Analogue Electronices;

Analogue Electronices; APPROVED ___________________________________________________________________________________ EXAMINATION PAPER: ACADEMIC SESSION 2011/2012 Campus Medway School Engineering Department Engineering Systems Programme BEng Engineering Suite COURSE TITLE Analogue Electronics COURSE CODE ELEE0052 LEVEL Two Date and Duration (incl. reading time) May 2012, 2 Hours Paper Set By Dr R Wu INSTRUCTIONS TO CANDIDATES & INFORMATION FOR INVIGILATORS The attention of the students is directed to the instructions printed on the answer book. Answer THREE of the following four questions. All questions carry equal marks. ---------- ___________________________________________________________________________________ Date & Duration of Exam: May 2012, 2 Hours Course Title: Course Code: Analogue Electronics ELEE0052 Page 1 of 7 APPROVED ___________________________________________________________________________________ Q1. (a) If a BJT transistor is operating in the active mode, what is the DC biasing requirement for the PN junctions? [4 marks] (b) An amplifier circuit is shown in Figure Q1(b). (i) What is the role of the resistor RE? Why? [5 marks] (ii) Discuss the role of the capacitor CE in terms of voltage gain. [5 marks] +VCC R1 RS RC CC2 CC1 CE vS R2 RL vo RE Figure Q1(b) (c) In the RC filter shown in Figure Q1(c)(i) (see page 3): R2=R4=1k?, RL=4.7k?, C1=1µF, C3=0.1µF. The Op-Amp is 741 type. The OpAmp can be modeled as a voltage-controlled voltage source, as shown in Figure Q1(c)(ii) (see page 3). Ri and Ro are the input and output resistances, respectively. Ao is the open-loop DC voltage gain. For µA741 Op-Amps, Ri=2M?, Ro=75?, Ao=2 × 105. If the input to the filter is a 100mV AC voltage source whose frequency will be varied between 1Hz and 1MHz logarithmically with 100 points-per-decade, write the PSPICE input file to calculate the frequency response of this filter. (In the Op-Amp model, a DC voltage source with V=0 can be connected between node 1 and the ground to simulate the grounded non-inverting terminal). [11 marks] Cont’d….. ___________________________________________________________________________________ Date & Duration of Exam: May 2012, 2 Hours Course Title: Course Code: Analogue Electronics ELEE0052 Page 2 of 7 APPROVED ___________________________________________________________________________________ Question 1(c) Continued. C3 C1 R4 R2 vi RL vo Figure Q1(c)(i) 5 2 vd Ri Ro 3 Aovd vo 0 1 Figure Q1(c)(ii) ___________________________________________________________________________________ Date & Duration of Exam: May 2012, 2 Hours Course Title: Course Code: Analogue Electronics ELEE0052 Page 3 of 7 APPROVED ___________________________________________________________________________________ Q2. (a) Figure Q2(a) shows a differential amplifier fed by a common-mode voltage signal vCM. If the output is taken single ended, assuming R>>rbe, ß/(ß+1)˜1, derive the voltage gain vc1/vCM or vc2/vCM by using the concept of the common-mode half-circuit. [10 marks] VCC RC RC vc 1 vc2 Q1 v Q2 v CM R CM I -VEE Figure Q2(a) (b) In the differential amplifier shown in Figure Q2(b) (see page 5), RC=5.1k?, R=100k?, I=1mA, ß=145. (i) What is the requirement for Q1 and Q2 in semiconductor device manufacturing? What is the role of the current source I? [5 marks] (ii) Determine the input differential resistance Rid. [4 marks] (iii) Determine the differential-mode gain Ad. [3 marks] (iv) Determine the common-mode rejection ratio (CMRR) in dB. [3 marks] Cont’d….. ___________________________________________________________________________________ Date & Duration of Exam: May 2012, 2 Hours Course Title: Course Code: Analogue Electronics ELEE0052 Page 4 of 7 APPROVED ___________________________________________________________________________________ Question 2(b) Continued. VCC +5V RC RC Vo Q1 Q2 Vi R I VEE -5V Figure Q2(b) ___________________________________________________________________________________ Date & Duration of Exam: May 2012, 2 Hours Course Title: Course Code: Analogue Electronics ELEE0052 Page 5 of 7 APPROVED ___________________________________________________________________________________ Q3. (a) How to determine the type of feedback in terms of the gain of a system? [3 marks] (b) In the common-emitter amplifier shown in Figure Q3(b): Rs=4k?, R1=10k?, R2=5k?, RE=1k?, RC=2k?, RL=5k?, VCC=12V. The transistor parameters are: ß=100, Cp=10pF, Cµ=2pF. (i) In this amplifier, the gain falloff in the high frequency band is due to the effects of which capacitors? [3 marks] (ii) Find its DC equivalent circuit, and hence determine IC, VB, VC and VE. [7 marks] (iii) Find the small signal equivalent circuit (gm, rp) for the transistor, and hence determine the midband gain. [5 marks] (iv) Find its high-frequency equivalent circuit. Use the miller-effect method to determine the total input capacitance and hence the upper 3-dB frequency fH (the dominant high-frequency). [7 marks] +VCC R1 Rs CC2 RC CC1 CE Vs R2 RL RE Figure Q3(b) ___________________________________________________________________________________ Date & Duration of Exam: May 2012, 2 Hours Course Title: Course Code: Analogue Electronics ELEE0052 Page 6 of 7 APPROVED ___________________________________________________________________________________ Q4. (a) An amplifier shown in Figure Q4(a) is intended to supply a voltage to floating loads (those for which both terminals are ungrounded) while making greatest possible use of the available power supply. Assuming that ideal Op-Amps are used; (i) Determine its voltage gain: vo/vi. [10marks] If R1=10k?, R2=5k?, R3=15k?, what is the voltage gain? Sketch the output voltage waveform vo for a 1V peak-to-peak sine wave applied at A. [8 marks] (ii) R2 R1 B R1 A v? R3 R1 v? R1 C Figure Q4(a) (b) For the Wien-bridge oscillator shown in Figure Q4(b). (i) If C=0.01µF, what is the value of R to generate an oscillation frequency of fo=10kHz? [4 marks] (ii) If R2=10k?, determine the value for R1. [3 marks] R2 R1 Vo R Vi R C C Figure Q4(b) ___________________________________________________________________________________ Date & Duration of Exam: May 2012, 2 Hours Course Title: Course Code: Analogue Electronics ELEE0052 Page 7 of 7 PLACE THIS ORDER OR A SIMILAR ORDER WITH US TODAY AND GET AN AMAZING DISCOUNT :)