Drift current - Analogue Electronics - Exam, Exams of Digital & Analog Electronics

Download Drift current - 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) Autumn 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 Question 1 is compulsory 1. (a) Briefly distinguish between avalanche breakdown and zener breakdown in a reverse-biased pn-junction. [5 marks] (b) Explain the term dynamic resistance when applied to a forward-biased diode. [5 marks] (c) Outline briefly the difference between drift current and diffusion current. [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) What is meant by donor doping and acceptor doping? Explain how the conductivity of a semiconductor material may be improved by either of the above processes. [5 marks] (f) Draw a sketch of the electromagnetic spectrum showing the main regions into which electromagnetic waves of different frequencies are allocated. [5 marks] (g) 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] (h) Briefly explain what is meant by the frequency spectrum of a complex signal. Sketch the frequency spectrum of a square wave. [5 marks] 2 2. The characteristics of an NPN transistor are listed below and may be assumed to be linear over the given range: IB IC (mA) @ VCE equal to (µA) 2V 8V 40 2.1 3.2 80 4.2 6.0 120 6.0 8.1 The transistor is used as a common emitter amplifier with a resistive load of 1.5kΩ, a supply voltage of 12V, and a quiescent base current of 80µA. (a) Plot the load line on the output characteristics and estimate the quiescent power dissipation in the transistor. [8 marks] (b) If the input signal is a base current of 80µAp-p about a mean value of 80µA, calculate the ac current gain, voltage gain, and power gain of the amplifier if the ac input resistance is 1.6kΩ. [12 marks] 3. (a) Draw the circuit diagram of a simple zener diode voltage regulator and briefly explain how the circuit minimises the effects of load current variations on the load voltage. [8 marks] (b) A zener diode has a reverse breakdown voltage of 10V and after this may be considered to be a linear resistance of 25Ω. Draw the circuit diagram and calculate the value of series resistor required for a simple voltage regulating circuit, using the diode above, which is to maintain 12V across a constant 600Ω load from a nominal 15V supply. [6 marks] (c) Determine the maximum variation that can be tolerated in the nominal 15V supply if the 12V load voltage is not to vary by more than 10%. [6 marks]