Download Exam Paper: Analogue & Digital Electronics, ELTR 8002, CIT, 2008/09 and more Exams Digital Electronics in PDF only on Docsity!
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2008/
Module Title: Analogue & Digital Electronics
Module Code: ELTR 8002
School: Electrical & Electronic Engineering
Programme Title: Bachelor of Engineering (Hons) in Electronic Engineering
Programme Code: EELXE_8_Y
External Examiner(s): Prof. G. Hurley, Dr. S. Foley Internal Examiner(s): Dr B V Donovan
Instructions: Full marks for Q1 and two other questions Note: Q1 carries extra marks.
Duration: 2 Hours
Sitting: Winter 2008
Requirements for this examination:
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.
Q
a) Show how Binary-weighted currents or voltages can be produced, by using a set of resistors of values R and 2R and a single reference voltage. Draw an appropriate circuit and describe its operation. (8 Marks)
b) Show how these currents could, in principle, be summed by an inverting Op- amp to give a simplified Digital (Switches On/Off) to analogue Voltage out. Comment on the shortcomings of this circuit when used as a DAC. (8 Marks)
c) Now sketch a simplified circuit using the R-2R network to produce a set of Binary-weighted Constant-Currents and describe how these would circumvent the series resistances of the ‘digital’ switches in b) above. (8 Marks)
d) Finally draw a circuit on could use to ‘steer’ the binary currents to two different destinations and hence produce a more appropriate DAC circuit. (8 Marks) e) Comment on potential problems on would encounter as one goes towards the higher resolution converters and steps a designer might take to counteract the problems. (8 Marks)
Q
a) Why is the principle of Pulse Width Modulation as a ‘control’ technique so popular? (3 Marks)
b) Give three examples where it finds application. (3 x 3 Marks)
I wish to vary the speed of a 12V, Permanent Magnet motor which drives a ‘potter’s wheel’, from about 50% to about 90% of its full speed. I intend using the circuit shown in Fig Q3 below for the purpose.
FIG Q
c) Describe how this circuit delivers ‘PWM’ showing the approximate wave-forms at BOTH inputs and the output of the Op-amp at, say 60:40 operation. (9 Marks)
d) If I require operation at about 700Hz and C is 0.01uF, estimate the values for Rv, R1 and R2, which will produce the range of adjustment required.
(9 Marks)
1M (^) 1M
1M
12V
C
Fixed Freq- Variable M:S
Ratio
R
R
Rv
Q4 Assume that for the transistors in this question K (^) p = 20μA/V 2 , Vto = +1V for the n-channel MOSFETs, Vto = -1V for the p-channel MOSFETs, and lambda = 0.
For the circuit shown in Fig Q4:
a) Calculate the voltages at nodes A, B and C. (12 Marks)
b) Define the conditions for saturation in an n-channel MOSFET and in a p- channel MOSFET.. (2 Marks)
c) What value of R1 causes M7 to come out of saturation? (6 Marks)
5V
M
20uA
W=10u L=1u
M2 M4 M6 M
M3 M 50k
W=10u L=1u W=20u L=1u
W=10u L=1u
W=10u L=1u
W=20u L=1u
W=5u L=1u A B (^) C
R
Figure Q
Useful Equations:
2 DS (^) 2 GS T
Kp W I V V L
= − …N-Channel (Sat): ( )
2 SD (^) 2 SG T
Kp W I V V L
= − …P-Channel (Sat.)
DS DS GS T DS
Kp W V I V V V L
….N-Channel Linear. …..
