CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2015
Module Title:
Electronic Engineering
Module Code:
ELTR7011
School:
School of Mechanical, Electrical and Process Engineering
Programme Title:
Bachelor of Engineering(Hons) in Electronic Engineering – Year 3
Programme Code:
EELXE_7_Y3
External Examiner(s):
Ms. Valerie Kenneally & Dr. Traolach O’Brien
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:
Winter 2015
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.
1
1.
(a)
For the Op-Amp in Fig.1(a), calculate all the currents and voltages around
the circuit and state which LED if any, lights (RED or GREEN).
(DC input voltages are V1 = 1.5V, V2 = -1V, R1 = 1k, R2 = 4k,
R3 = 0.5k). Note : V2 is a negative voltage.
(5 marks)
(b)
Analyse the Op-amp circuit shown in Fig.1(b) and calculate all the
currents and voltages around the circuit.
(DC input voltages are V1 = 6.5V, V2 = 4.5V)
(5 marks)
(c)
The Op-Amp shown in Fig.1(c) has a sinewave input of 𝑉1 = ±2𝑉 at a
frequency of 5kHz and V2 has a dc value of -1V. Draw a detailed graph of
both input and output waveforms using a proper scale and explain your
output.
(5 marks)
An amplifier is displayed in Fig.1(d).
It has a sinewave input of 𝑉1 = ±1.5𝑉 at a frequency of 2kHz.
(i)
Draw the output signal to a correct scale.
(ii)
If the frequency of the input is increased to 50kHz
what changes if any occur at the output.
(Typical Op-Amp values that you are familiar with may be used).
(5 marks)
(d)
(e)
(f)
Write a technical note on the AC-Performance of Op-Amps.
Your explanation should include UGB, f c (OL ) , f c (CL) , and a
frequency response curve to demonstrate your understanding.
(5 marks)
An analogue filter has a transfer function given by
𝑠 2 + 2𝑠
𝐻(𝑠) = 2
2𝑠 − 0.5𝑠 + 8
Sketch its output response and show how you arrived at this response.
What type of filter does H(s) represent?
(5 marks)
(g)
A buck converter has an input of 50V and an output of 20V. The load
resistor is 9Ω. The switching frequency is 25kHz, L = 2 mH,
C = 150µF. Find the duty cycle, the minimum and maximum inductor
currents. (A circuit diagram is required).
(5 marks)
(h)
Design a circuit to accomplish the following:A sensor has an output sinusoidal voltage of ±275mV at f = 5kHz. This
voltage is fed into a single-supply Op-Amp running off +5V. The output
should be centered at 2.8V, with a swing that reaches from 1.9V above
ground to 3.7V. Assume that because of the frequencies involved, ac
coupling is not an option.
(5 marks)
2
2. (a)
The circuit shown in Fig.2(a) has inputs :
V1 = 1.5V Sinewave and
V2 = 2.5V Sinewave.
Both have a frequency of 1kHz.
Calculate, from first principles, the output voltage of the Op-Amp.
Sketch on the same graph, the output voltage (Vout ) and both input
voltages (V1 and V2).
(15 marks)
(b)
Write a technical note on passive Band-Stop Filters.
(Your note should include circuit diagram, Bode plot, break frequencies).
(8 marks)
(c)
An Op-amp circuit is shown in Fig.2(c)
Using the two voltage probes shown (Vin, and Vout), draw a sketch
showing the two waveforms and explain what this circuit does.
Suggest Applications for this circuit.
(7 marks)
3. (a)
Design an Active Non-Inverting 2nd –Order Low-Pass filter that has a
gain of 8.5dB and a cut-off frequency, fc = 1kHz.
Sketch the frequency response curve for the filter, showing relevant
information points.
(Only 1kΩ, 2kΩ, 3kΩ and 5kΩ resistors are available for your design).
(15 marks)
(b)
A filter circuit is shown in Fig.3(b). Sketch its’ frequency and phase
responses by calculating suitable values using the transfer function given.
|𝐻(𝑗𝜔)| =
𝜔2 𝑅1 𝑅2 𝐶1 𝐶2
√[(1 − 𝜔 2 (𝑅1 𝑅2 𝐶1 𝐶2 )) ]2 + [ 𝜔𝑅1 ( 𝐶1 + 𝐶2 )]2
State the Filter Classification (type)
3
(15 marks)
4. (a)
Draw a circuit for an Op-Amp series regulator with short-circuit protection.
Outline the function of each element and calculate the voltages/currents around
the circuit, given the following parameters (usual notation):Vin = 18V ,Vz = 6.3V , R1 = 1kΩ , R2 = 2.2kΩ , R3 = 5.6kΩ , R4 = 10Ω
(12marks)
(b)
If a load resistor of RL = 150Ω is placed across R2 and R3, what effect, if any
does this have on the circuit?
If RL drops to 50Ω, what happens?
(4 marks)
(c)
Design a Beam Activated Alarm system with a Red-LED as a visual indicator
and a Buzzer as an audio indicator. Your design should include at least one
Op-Amp. Explain clearly your design and its operation.
(14 marks)
U1(V+)
U1
7
V2
VALUE=-1V
3
R3
6
2
4
1
5
500
741
V1
VALUE=1.5V
R1
1k
U1(V-)
R2
4k
Fig.1(a)
4
D1
D2
LED-RED
VF=2V
IMAX=10mA
LED-GREEN
VF=2V
IMAX=10mA
R2
5.6k
U1(V+)
U1
R1
7
V2
VALUE=4.5V
V(Op-Amp)
3
2.2k
6
2
4
1
5
R3
5.6k
741
V1
VALUE=6.5V
R5
2k
R4
2.2k
U1(V-)
Fig.1(b)
U1(V+)
V1
OFFSET=0
FREQ=5k
PHASE=0
THETA=0
AMP=2V
U1
7
R1
V(Op-Amp)
3
4k
6
4
1
5
2
V2
VALUE=-1V
741
R4
3k
U1(V-)
R3
5k
Fig.1(c)
5
U1(V+)
U1
R1
7
V1
OFFSET=0
FREQ=2k
PHASE=0
THETA=0
AMP=1.5V
V(Op-Amp)
3
5k
6
4
1
5
2
741
R4
3.3k
U1(V-)
R3
10k
Fig.1(d)
R2
5.6k
-15V
4
1
5
U1
Vout
R1
2
6
3.3k
3
R3
7
V1
AMP=1.5V
FREQ=1k
OFFSET=0
PHASE=0
THETA=0
741
2.2k
V2
AMP=2.5V
OFFSET=0
FREQ=1k
PHASE=0
THETA=0
+15V
R4
12k
Fig.2(a)
6
R2
10k
-15V
4
1
5
U1
Vin
AMP=1V
FREQ=1k
OFFSET=0
PHASE=0
THETA=0
Vout
R1
2
6
10k
3
RV1
7
20k
741
C1
100%
10nF
+15V
Fig.2(c)
R1
10k
U1(+)
C1
C2
Vout-Active
3
6
30nF
50nF
2
R2
3.8k
4
1
5
Vin
7
U1
741
U1(-)
Fig.3(b)
7