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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2008/
Module Title: Analogue Electronics 3
Module Code: ELTR 6013
School: Electrical & Electronic Engineering
Programme Title: Bachelor of Engineering in Electronic Engineering – Stage 2
Programme Code: EELXE_7_Y
External Examiner(s): Mr. D. Denieffe Dr. P. O’Sullivan
Internal Examiner(s): Dr. M. Cranitch
Instructions: Answer Question 1 and two other questions
Duration: 2 Hours
Sitting: Autumn 2009
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
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Q1. (a) Draw the circuit diagrams of (i) an integrator, and (ii) a differentiator. (8 Marks) (b) In relation to an inverting comparator with non-zero voltage reference, sketch time- related waveforms of input and output when a sinusoidal signal is applied. Include the circuit diagram in your answer. (8 Marks) (c) State the conditions necessary for a circuit to oscillate. What are these called? (8 Marks) (d) Define ‘mark space ratio’ and ‘duty cycle’ as applied to a rectangular waveform. For a waveform with duty cycle of 60%, indicate the mark space ratio. (8 Marks) (e) Draw the circuit diagram of a regulated dual power supply, incorporating monolithic regulators, to provide ±12V, 600mA dc from a mains supply of 220Vrms. Indicate the minimum power rating required of the transformer secondary windings. (8 Marks)
Q2. (a) With the aid of appropriate sketches, explain the terms ‘slew rate’ and ‘transition frequency’ as applied to an op-amp. In each case, quote the figure typical of the 741 op- amp. (12 Marks) (b) Draw the circuit diagrams of (i) three-input summing amplifier, and (ii) difference amplifier. (8 Marks) (c) For each of the circuits in part (b), derive the equation for output voltage. (10 Marks)
Q3. (a) Explain what is meant by ‘negative feedback’, and list the effects it has on an amplifier circuit. (10 Marks) (b) Show that, when negative feedback is applied to an amplifier, the resulting gain is given by Af = A
1 +βA
. (8 Marks)
(c) An amplifier has the following characteristics without feedback: A = 100, fL = 120Hz, f (^) H = 15kHz, Ri = 5kΩ, Ro = 600Ω, D (distortion) = 1%. Determine the characteristics when 1% voltage negative feedback is applied in series with the input. (12 Marks)
Q4. (a) With reference to a power amplifier, distinguish between class-A and class-B operation. State the ‘angle of flow’ applicable in each case. (10 Marks) (b) Explain ‘cross-over distortion’ as applied to a class-B push-pull amplifier. How can this form of distortion be eliminated? (8 Marks) (c) A class-B complementary-pair power amplifier has a supply voltage of 30V and load resistor of 12Ω. If the transistors are operated at 80% of the maximum values, determine (i) a.c. output power, (ii) d.c. input power, and (iii) efficiency. (12 Marks)
