Frequency Response - Analogue Electronics - Exam, Exams of Digital & Analog Electronics

Download Frequency Response - Analogue Electronics - Exam and more Exams Digital & Analog Electronics in PDF only on Docsity! Cork Institute of Technology Bachelor of Engineering in Applied Electronics Design – Stage 1 Bachelor of Engineering in Communications Systems – Stage 1 Bachelor of Engineering in Electronic Automation & Robotics – Stage 1 (NFQ Level 7) Summer 2007 ANALOGUE ELECTRONICS (Time: 3 Hours) Answer Question 1 [40 marks] and any three other questions [each 20 marks] Examiners: Mr. M. O’Gorman Mr. D. O’Mahony Mr. D. Denieffe Dr. R. O Dubhghaill 1. Compulsory (a) Explain what is meant by the frequency response of an amplifier. Outline the characteristics of an amplifier which may be ascertained from the plot of such a response. [5 marks] (b) Draw a sketch of the electromagnetic spectrum showing the main regions into which electromagnetic waves of different frequencies are allocated. [5 marks] (c) Explain why the output voltage of a common emitter transistor amplifier is 180° out of phase with the input voltage. [5 marks] (d) Show how the maximum power dissipation curve for a transistor may be drawn on the transistor’s output characteristics. Illustrate the direction of curve displacement if the ambient operating temperature of the device is to be increased. [5 marks] (e) Outline briefly the difference between drift current and diffusion current. [5 marks] (f) Briefly distinguish between avalanche breakdown and zener breakdown in a reverse-biased pn-junction. [5 marks] (g) Explain the term dynamic resistance when applied to a forward-biased diode. [5 marks] (h) Sketch typical output characteristics for a common emitter transistor and illustrate the region where the transistor is said to be saturated. What bias condition exists at the collector-base junction (VCB) when a transistor operates in the saturated region? [5 marks] 2 2. VCC +15V( ) R1 R2 RE 0 V CE RL Figure 1 (a) Explain the function of each of the five labelled components in Figure 1. [6 marks] (b) The common emitter amplifier of Figure 1 operates with quiescent conditions VCE = 5.0V, and IC = 4mA. The base and emitter voltages measured under these conditions are 1.5V and 0.9V respectively. If the dc current gain of the transistor (β) is 44, calculate suitable values for the four labelled resistors. [8 marks] (c) Calculate the minimum value of CE required to prevent ac feedback if the lowest input signal frequency is 20 Hz. [6 marks] 3. (a) Draw the circuit diagram of a simple zener diode regulator and briefly explain how the circuit minimises the effects of supply voltage variations on the load voltage. [4 marks] (b) A zener diode has a reverse breakdown voltage of 4.7V and may be considered a linear resistance of 4Ω for voltages beyond this value. It is to be used in a simple voltage regulator circuit to maintain 5.0V across a 200Ω load from a nominal 10V supply. Calculate a suitable value of series resistor. [4 marks] (c) Determine the power dissipated in the series resistor and in the diode. [6 marks] (d) Calculate the change in load voltage if the supply voltage increases by 10%. [6 marks]