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Oscillators - Telecommunications - Exam, Exams of Telecommunication electronics

Amity University - BiharTelecommunication electronics

The past exam paper of Telecommunications. Some key points for this exam are: Oscillators, Maximum Power Transfer Theorem, Impedance Matching, Impedances, Reflection Coefficients, Smith Chart, Smith Chart Provided, Load Impedances, Blocking, Passing

Typology: Exams

2012/2013

Uploaded on 04/15/2013

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Cork Institute of Technology
Bachelor of Engineering in Communications Systems-Award
(NFQ Level 7)
Autumn 2006
Telecommunications Hardware
(Time: 2 Hours)
Answer four questions, including at least one
question from each section
[All questions are worth equal marks]
Use separate answer books
for each Section
Values for constants;
Speed of light in a vacuum c = 2.998 x 108 m s-1
electron charge q = 1.602 x 10-19 C
Planck constant h = 6.625x 10-34 J
Boltzmann constant k = 1.381x 10-23 J K-1
Examiners: Mr. J. Berry
Dr. R. O’Dubhghaill
Dr. O. Gough
Dr. J. Barrett
Section A (Dr. J. Barrett)
Question 1 (Impedance matching)
(a) What is the Maximum Power Transfer Theorem and how is it used in
impedance matching? (3 marks)
(b) Plot the following impedances and reflection coefficients on the ordinary
Smith Chart provided (4 marks)
i. 15-j30Ω
ii. 40+j20Ω
iii. °∠1202.0
iv. °−∠ 159.0
(c) Use the Z-Y Smith Chart provided to design L-C matching networks to
match the following source and load impedances at 900MHz
i. 30+j20Ω source to a 100Ω load, blocking DC (9 marks)
ii. 15-j10Ω source to a 40+j30Ω load, passing DC (9 marks)
pf3
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Cork Institute of Technology

Bachelor of Engineering in Communications Systems-Award

(NFQ Level 7)

Autumn 2006

Telecommunications Hardware

(Time: 2 Hours)

Answer four questions, including at least one question from each section [All questions are worth equal marks]

Use separate answer books

for each Section

Values for constants; Speed of light in a vacuum c = 2.998 x 10 8 m s- electron charge q = 1.602 x 10 -19^ C Planck constant h = 6.625x 10 -34^ J Boltzmann constant k = 1.381x 10 -23^ J K-

Examiners: Mr. J. Berry Dr. R. O’Dubhghaill Dr. O. Gough Dr. J. Barrett

Section A (Dr. J. Barrett)

Question 1 (Impedance matching)

(a) What is the Maximum Power Transfer Theorem and how is it used in impedance matching? (3 marks) (b) Plot the following impedances and reflection coefficients on the ordinary Smith Chart provided (4 marks) i. 15-j30Ω ii. 40+j20Ω iii. 0. 2 ∠ 120 ° iv. 0. 9 ∠ − 15 ° (c) Use the Z-Y Smith Chart provided to design L-C matching networks to match the following source and load impedances at 900MHz i. 30+j20Ω source to a 100Ω load, blocking DC (9 marks) ii. 15-j10Ω source to a 40+j30Ω load, passing DC (9 marks)

Question 2 (Amplifiers)

(a) How do the four s-parameters relate to the circuit parameters of an RF amplifier? (4 marks) (b) Why are s-parameters preferred to other two port network parameters (e.g. Z or Y-parameters) for RF design? (4 marks) (c) A transistor has the following s-parameters at 432MHz:

i. Assuming unilaterality, what should be the source and load reflection coefficients to obtain a maximum gain amplifier? (2 marks) ii. Again assuming unilaterality, use the Z-Y Smith Chart to design LC source and load matching networks (blocking DC) to use this transistor as a maximum gain amplifier with a 50Ω source and a 50 Ω load (9 marks)

(d) Why are s-parameters not commonly used in power amplifier design? (3 marks) (e) What is “distortion” in power amplifiers and why does it occur? (3 marks)

Question 3 (Oscillators)

(a) What are the Berkhausen criteria for oscillation? (2 marks) (b) Draw the circuit diagram for a tuned collector oscillator and show how it meets the Berkhausen criteria (8 marks) (c) Draw the circuit diagram for a Colpitts L-C oscillator, explain its principle of operation and show how it meets the Berkhausen criteria (8 marks) (d) What are the two main types of noise in an oscillator, what causes them and what effects can they have on communications circuits using oscillators? (7 marks)

Question 4 (Filters)

(a) What is “loading” on an R-C filter and how does it affect its circuit parameters? (5 marks) (b) How can an op-amp be used to prevent the loading effect? (5 marks) (c) Daw the circuit diagram of a 1st^ order high pass active filter (5 marks) (d) An RC high pass filter is made up from an 230Ω resistor and a 200 pF capacitor. i. Calculate its cut-off frequency (ωc) and the magnitude of the transfer function at one eighth of the cut-off frequency (ωc/8) (5 marks) ii. A resistor of 300Ω is added as a load to this filter. Calculate the new cut-off frequency (ωc(LOAD) )and the magnitude of the transfer function at half of the cut-off frequency (ωc(LOAD) /2) (5 marks)

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