COMSATS Institute of Information Technology
Attock Campus
Program: BS (EE) – IV
Spring 2013, Sessional Examination 02
Course: Electronics – II (EEE –232)
Section A: Objective (Solution)
Time Allowed: 15 Minutes
Dated: April 22, 2013(1500-1600 Hrs)
Points: 10
Person Responsible: Muhammad Tilal
Name: _____________________________________Registration #: _____________________________
_____________________________________________________________________________________
Instructions: Every question has only one correct answer, choosing more than one answer will be
awarded 0 points for that question. Encircle the correct answer properly.
01. Which of the following statements is generally true about feedback?
(a) Both amplifiers and oscillators use negative feedback.
(b) Both amplifiers and oscillators use positive feedback.
(c) Positive feedback is used in oscillators while negative feedback is used in amplifiers.
(d) Negative feedback is used in oscillators while positive feedback is used in amplifiers.
(e) None of the above.
02. In filters, over shoot and ringing are caused by
(a) Poor roll off rate.
(b) Non linear phase response.
(c) Linear phase response.
(d) All of the above.
03. Chebyshev filter of order n have
(a) n ripples in the pass band.
(b) n+1 ripples in the pass band.
(c) n-1 ripples in the pass band.
(d) n-2 ripples in the pass band.
04. Phase response of a filter represents
(a) Phase shift induced by filter as a function of amplitude.
(b) Phase shift induced by filter as a function of frequency.
(c) Phase shift induced by filter as a function of time.
(d) None of the above.
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05. Which of the following input signals to integrator can cause negative or positive saturation?
(a) A positive DC voltage.
(b) A negative DC voltage.
(c) A sinusoidal waveform.
(d) Both options (a) and (b).
(e) Both options (a) and (c).
06. For a good band pass filter
(a) Q factor should be low.
(b) Q factor should be high.
(c) Q factor has no effect on performance.
(d) None of the above.
07. Center frequency for a band pass filter is defined as
(a) The frequency at which the filter gain is minimum.
(b) The frequency at which the filter gain is maximum.
(c) The frequency at which phase response is linear.
(d) The frequency at which the phase response is exponential.
08. -3 dB bandwidth is the bandwidth defined by frequencies at which
(a) The filter gain is 3 dB above its maximum value.
(b) The filter gain is 3 dB down its maximum value.
(c) The filter gain is exactly -3 dB.
(d) None of the above.
09. The circuit in the figure 01 is
(a) Is a low pass filter.
(b) High pass filter.
(c) Band pass filter.
(d) Band stop filter.
10. Which of the following statements is true regarding analog and digital filters?
(a) Analog filters have higher latency as compared to digital filters.
(b) Analog filters have lower latency as compared to the digital filters.
(c) Both analog and digital filters have comparable latency.
(d) None of the above.
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Figure # 01
COMSATS Institute of Information Technology
Attock Campus
Program: BS (EE) – IV
Spring 2013, Sessional Examination 02
Course: Electronics – II (EEE –232)
Sections B: Short Questions & Design Problems (solution)
Time Allowed: 45 Minutes
Dated: April 22, 2013(1500-1600 Hrs)
Points: 20
Person Responsible: Muhammad Tilal
Name: _____________________________________Registration #: _____________________________
_____________________________________________________________________________________
Note: - Don’t write anything on Question Paper except your name & Regn. No.
Instructions
01.
02.
03.
04.
05.
Try to be neat and organized.
Avoid giving unnecessary details and be concise.
Draw circuit diagrams and equivalent circuits where necessary.
There is no choice in the paper and all the questions are compulsory.
Clearly state the assumptions you make while answering a question. Failure to mention the
assumptions clearly can reduce the points.
Good Luck!
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Section B: Short Questions and Design Problems
Question # 01: Explain why a feedback resistor Rf is used in parallel with the capacitor in the design of
practical integrators.
(5 Points)
Answer: The feedback resistor Rf is used in parallel with the capacitor in the design practical integrators
in order to avoid saturation because of the input bias current.
Question # 02: Design an op amp summing amplifier to produce an output equal to - (4V1+V2+0.1V3)
assuming the value of Rf=60kΩ. Also calculate the value for compensating resistor Rc.
(5 Points)
Answer: Comparing the given output with the general output equation of the summing amplifier
Vo= - [(Rf/R1)*V1 + (Rf/R2)*V2 +(Rf/R3)*V3] we get
Rf/R1= 4, Rf/R2= 1, Rf/R3= 0.1. With the value of Rf= 60kΩ, R1=15 kΩ, R2=60 kΩ, R3= 600 kΩ.
Rc= Rf||R1||R2||R3 = 9.8 kΩ.
Question # 03: An application requires an active band pass filter to be designed having a pass band of
6 KHz and upper cut off frequency of 10 KHz with and closed loop gain of 10. Design a band pass filter
with the above mentioned specifications using ONLY low pass active filters having slope of
20dB/decade. Also draw the resulting circuit diagram.
(10 Points)
Answer: For the required band pass filter
Upper cut off frequency = f2= 10 KHz.
Bandwidth= BW= 6 KHz.
Lower cut off frequency= f2= (10 - 6) KHz = 6 KHz.
As only active low pass filters can be used to design the required band pass filter we need to design two
active low pass filters with the cut off frequencies of 4 and 10 KHz and subtract their responses to get
the band pass filter response. As the given slope is 20dB/ decade, first order filters have to be
designed.
For both low pass filters, keeping the closed loop gain equal to 10, the values for Rf and RG are calculated
as under
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1+ (Rf/RG) = 10 => Rf/RG = 9 => RG= Rf/9.
Assuming Rf= 18kΩ, RG= 2kΩ.
For LPF 1 with cut off frequency, fc=f2= 4 KHz
fc= 1/ (2πR1C1)
Assuming C1= 0.02µF, R1 is calculated as 1989.43Ω ≅ 2kΩ.
For LPF 2 with cut off frequency, fc=f2= 10 KHz
fc= 1/ (2πR2C2)
Assuming C2= 0.02µF, R2 is calculated as 795.7Ω ≅ 800Ω.
The End
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