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THE MANCHESTER METROPOLITAN UNIVERSITY
FACULTY OF SCIENCE AND ENGINEERING
DEPARTMENT OF ENGINEERING AND TECHNOLOGY
SESSION 2004/
Examination for the BEng (HONS) ELECTRICAL AND ELECTRONIC ENGINEERING HND ELECTRONIC ENGINEERING YEAR/STAGE ONE
UNIT 64EE1102 : ANALOGUE ELECTRONICS
Tuesday 26 April 2005
9:30 am to 11.30 am
Instructions to Candidates
Attempt FOUR questions.
Marks for sections of questions are shown in parentheses.
You are permitted to use any calculator which conforms to the Faculty Standard.
S131 25/08/
- (a) A common emitter transistor amplifier has been designed using an NPN bipolar transistor. The amplifier uses base potentiometer and emitter resistor biasing in which the emitter resistor is NOT decoupled by a capacitor.
From first principles and using h-parameters, derive an expression for the small signal voltage gain of the amplifier. Assume hoe is so small that it can be neglected. Your answer should include a circuit diagram and a small signal equivalent circuit. [14]
(b) An amplifier similar to the above has been INCORRECTLY designed. ALL the resistor values in the circuit have been chosen to be 1KΩ. Redesign the circuit for correct operation using the following information:
VCC = 10 V h (^) fe = 100 I (^) CQ = 0.5mA VCQ = 5 V
Use the nearest preferred value (NPV) for resistors in your design. [11]
- (a) The output stage of a power amplifier dissipates 40 W. It comprises two identical transistors with θJC = 0.5 °C/W. They are both bolted onto one heatsink. If the maximum permissible transistor junction temperature is 150 °C and the maximum ambient temperature is 40 °C:
(i) What must the maximum thermal resistance of the heatsink, θCA, be? [6]
(ii) What is the maximum temperature of the heatsink? [5]
(b) The thermal resistance, θCA, of the best available heatsink for the amplifier described above is 3 °C/W. Fan cooling is therefore used which effectively reduces θCA to 1 °C/W.
(i) What would be the junction temperature now? [8] (ii) By how much can the power dissipation be increased before the maximum junction temperature is reached? [6]
25/08/2005 continued
- (a) Draw an a.c. coupled, low frequency circuit for a J-FET Common Source amplifier [3]
(b) Using the small signal equivalent model for a J-FET, where gm is the mutual conductance, show that the mid-band voltage gain for Common Source amplifier is gm RL assuming source a.c. decoupling is employed. [12]
(c) For ONE of the following, write an essay describing:
(i) The internal structure of a voltage mode, 5 transistor differential input operational amplifier. Outlining how the use of current mirrors, active loads and current sinks may enhance the performance of this circuit.
(ii) The circuit topology and operation of MOSFET, tri-state binary logic. [10]
25/08/2005 continued
- Figure Q5 depicts the trajectories of 6 holes within a vertical structure, silicon, PNP Bipolar Junction Transistor.
FIGURE Q5 (© Milward 1955)
(a) State how recombination and increased base width changes BJT operation. [5]
(b) State what is occurring when the base region is energised to the potential depicted by the letters A & B. [5]
(c) Sketch an electronic circuit that could provide these bias conditions. [5]
(d) Labelling the holes shown, (from left to right), numbers 1 -> 6; creating a table to help in your explanation, state the conditions that gave rise the individual path of holes 4 & 5. [10]
S131 25/08/2005 END
