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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2008/
Module Title: Electronic Engineering
Module Code: ELTR
School: School of Electrical & Electronic Engineering
Programme Title: Bachelor of Engineering in Electronic Engineering – Year 3
Programme Code: EELXE_7_Y
External Examiner(s): Mr David Denieffe & Dr. Paula O’Sullivan
Internal Examiner(s): Dr. P. O’Connor
Instructions: Answer QUESTION 1 (worth 40 marks) and TWO other questions (worth 30 marks each)
Duration: 2 HOURS
Sitting: Summer 2009
Requirements for this examination: Graph paper, Log Tables
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
- (i) Calculate the closed-loop-gain( ACL ) and the feedback ratio( β ) for both
circuits shown in Fig.1(i). (5 marks)
(ii) Find ACL of the amplifier shown in Fig.1(ii) when a) AOL =∞ b) AOL = 106 c) AOL = 102 Comment on your findings. (5 marks)
(iii) Explain (using a circuit diagram) why calculations for the output error voltage caused by input offset voltages are the same for both inverting and non-inverting Op-Amp configurations. (5 marks)
(iv) The Op-Amp shown in Fig.1(iv) has a slew rate (SR) of 0. 5 V / μ s.
If the input is a ramp waveform (t in μ s ) as shown, what is the
maximum ACL that the amplifier can have without exceeding its slew rate. Show the output signal with correct values. (5 marks)
(v) Write a technical note on the AC-Performance of Op-Amps. Your explanation should include the UGB, f (^) c ( OL ), f (^) c ( CL ), and a frequency response curve to demonstrate your understanding. (5 marks)
(vi) Indicate how a simple band-pass filter and a simple band-stop filter may be created using LP and HP filters. (5 marks)
(vii) Design a buck converter to produce an output of 18V across a 10 Ω load when V (^) IN = 48 V. The output ripple must be ≤ 0. 5 %and continuous operation is required (assume f = 40 kHz ). (5 marks)
(viii) A sensor has an output voltage of ± 0. 1 V and this is fed into a single-supply Op-Amp operating off +5V. The output should be centered around 2.5V with a swing ± 1 V. Design such a circuit, assuming ac coupling is not necessary. (5 marks)
(c) Design a 2nd^ order VCVS, low-pass Butterworth filter with a cutoff frequency of 2.5 kHz. The gain in the pass-band should be 2. (State any assumptions.)
[A general configuration for a 2nd^ order HP/LP Butterworth filter is shown in Fig.3(c), as well as Tables]
(8 marks)
4. (a) The Op-Amp shown in Fig.4(a) has a slew rate (SR) of 0. 5 V / μ s.
The amplifier must be capable of amplifying the following input signals:-
(i) v 1 (^) = 0. 01 sin( 106 t ) (ii) v 2 (^) = 0. 05 sin( 350 x 103 t ) (iii) v 3 (^) = 0. 1 sin( 200 x 103 t ) (iv) v 4 (^) = 0. 2 sin( 50 x 103 t )
Determine whether the output will be distorted due to the SR limitations on any input. If so, find a remedy (other than changing the input signals!).
(20 marks)
(b) An Op-Amp with a UGB = 1MHz is configured as a non-inverting amplifier with a gain of 10 and then as an inverting amplifier with a gain of -10. Find in each case (i) fc ( CL )
(ii) A ( CL ) ,when input signal frequency is 150kHz
Sketch your results on a frequency response plot for non-inverting case.
(10 marks)
C 1 0.33C^ C^ 2C^ 2C^ 2C^ 2C
- Circuit Element Values
- Gain
- R 1 1.422 1.126 0.824 0.617 0.521 0.
- R 2 5.399 2.250 1.537 2.051 2.429 2.
- R 3 Open 6.752 3.148 3.203 3.372 3.
- R 4 0 6.752 9.444 16.012 23.602 32.
- 1 – Resistance in kilohms for a K parameter of
