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MU Electronics and Telecom Engineering (Semester 8)
May 2013
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 (a) Explain Large Signal characterization with reference to load pull contours. How is it measured?
5 M
1 (b) What are the causes of low frequency noise and high frequency noise associated with the mixer?
5 M
1 (c) Define and explain with neat diagram noise correlation matrix for general noisy two port network.
5 M
1 (d) What is unilateral figure of merit of an amplifier?
5 M

2 (a) If the transistor has following S-parameters at 5Ghz with 50Ω impedance.
S11=0.6∠–175°
S12=0.02∠20°
S21=2.2∠35°
S22=0.6∠-95°
Determine the stability criteria and plot the stability circles.
10 M
2 (b) Derive the parameters of an Amplifier:
(i) Power gain (G)
(ii) Available gain (GA)
(iii) Transducer gain (GT)
10 M

3 (a) Explain using suitable diagrams two methods of designing broadband amplifier.
10 M
3 (b) A BJT with IC = 30 mA and VCE = 10V is operated at a frequency of 1 GHz in a 50Ω system. Its S-parameters are -
S11=0.73∠175°
S12=0
S21=4.45∠65°
S22=0.21∠-80°
Determine whether the transistor is unconditionally stable. If yes, calculate optimum terminations, GSmax, GLmax, GTUmax.
10 M

4 (a) A certain GaAs MESFET has following noise figure parameters measured at Vds = 50, Ids = 20 mA with 50Ω resistor once for frequency of 9 GHz,
Fmin = 4dB, Γopt=0.55∠175, R0= 4Ω.
Plot noise figure circles for given values of f1 at 2, 2.5, 3.5, and 4.5 dB.
15 M
4 (b) Define stability. List the various criteria for stability.
5 M

5 (a) If a one port microwave diode has Γin=1.5∠60° with respect to Z0=50Ω. Design an oscillator for desired frequency of 10GHz.
12 M
5 (b) For a two port oscillator at steady state oscillations prove that if τLτin=1 then τinτout=1
8 M

6 A certain MESFET is biased for large signal class A operation with following small signal S-parameters at 5GHz:
S11=0.55∠-150°
S12=0.04∠20°
S21=3.5∠170°
S22=0.45∠-30°
The large signal forward transmission coefficient S21 is measured to be S21=2.1∠180°. Design a large-signal class A amplifier with maximum transducer gain in a 50Ω system. Assume (±)0.5dB error in gain. What is the high-power amplifier gain?
20 M

7 (a) Write a note on optimal loading used in 1+PA design.
10 M
7 (b) A wideband amplifier (2-4 GHz) has gain of 10dB, an O/P power gain of 10dBm and a noise figure of 4dB at room temperature. Find the output noise power in dBm.
10 M

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