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SENIOR CERTIFICATE EXAMINATIONS/
NATIONAL SENIOR CERTIFICATE EXAMINATIONS
ELECTRICAL TECHNOLOGY: ELECTRONICS
2022
MARKS: 200
TIME: 3 hours
This question paper consists of 25 pages, a 1-page formula sheet
and 4 answer sheets.
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Electrical Technology Grade 12 NSC June 2022 QP (Eng)
Grade 12 Electrical Technology question paper from the NSC June Exam 2022 (English), 30 pages. Read online or download the free PDF.
Electrical Technology · Grade 12 · NSC June Exam · 2022. Question paper, 30 pages. Read online or download the PDF.
- Subject
- Electrical Technology
- Grade
- Grade 12
- Document type
- Question paper
- Year
- 2022
- Exam period
- NSC June Exam
- Curriculum
- CAPS
- Pages
- 30
- File size
- 733.3 KB
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Electrical Technology: Electronics 2 DBE/2022
SC/NSC
INSTRUCTIONS AND INFORMATION
1. This question paper consists of SIX questions.
2. Answer ALL the questions.
3. Answer the following questions on the attached ANSWER SHEETS:
QUESTIONS 4.2.1, 4.2.2, 4.3.3 and 4.7.3
QUESTIONS 5.3.5, 5.4.6, 5.6.1 and 5.6.2
QUESTION 6.5.3
4. Write your centre number and examination number on every
ANSWER SHEET and hand them in with your ANSWER BOOK, whether you
have used them or not.
5. Sketches and diagrams must be large, neat and FULLY LABELLED.
6. Show ALL calculations and round off answers correctly to TWO decimal
places.
7. Number the answers correctly according to the numbering system used in this
question paper.
8. You may use a non-programmable calculator.
9. Calculations must include:
9.1 Formulae and manipulations where needed
9.2 Correct replacement of values
9.3 Correct answers and relevant units where applicable
10. A formula sheet is attached at the end of this question paper.
11. Write neatly and legibly.
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Electrical Technology: Electronics 3 DBE/2022
SC/NSC
QUESTION 1: MULTIPLE-CHOICE QUESTIONS
Various options are provided as possible answers to the following questions. Choose
the answer and write only the letter (AD) next to the question numbers
(1.1.1 to 1.1.15) in the ANSWER BOOK, e.g. 1.16 D.
1.1 The layer(s) of the skin that is/are affected by a third-degree burn would be …
A the outer layer.
B the second layer.
C all layers of the skin.
D None of the above-mentioned (1)
1.2 The power factor in an RLC series circuit will be lagging if VL …
A is greater than VC.
B is less than VC.
C is equal to VC.
D None of the above-mentioned (1)
1.3 A circuit has a resistance of R ohm, inductance of L henry and a capacitance
of C farad connected in series. The power factor of the circuit will be at
unity (1) when …
A XL is less than XC.
B XL is greater than XC.
C XL = XC.
D R = 0. (1)
1.4 Which ONE of the following conditions exists in a resonant parallel RLC
circuit?
A The impedance is minimum.
B The impedance is maximum.
C The total current is maximum.
D The power factor is lagging. (1)
1.5 The … is a device that relies on the creation of an electric field within the
channel to control current flow.
A Darlington pair transistor
B unijunction transistor
C field-effect transistor
D operational amplifier (1)
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Electrical Technology: Electronics 4 DBE/2022
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1.6 When applying a signal to the inverting input of an op amp, phase shift is
achieved by the …
A cut-off frequency.
B internal amplifier circuits.
C notch frequency.
D unity-gain frequency. (1)
1.7 Negative feedback in an op amp …
A increases the input and output impedances.
B decreases the output impedance and the bandwidth.
C increases the input impedance and the bandwidth.
D does not affect impedances or the bandwidth. (1)
1.8 Open-loop gain with reference to op amps is when …
A a feedback resistor is connected from the output to the inverting input.
B no feedback resistor is connected from the output to the input.
C a capacitor is connected from the output to the inverting input.
D a feedback resistor is connected from the output to the non-inverting
input. (1)
1.9 When a triangular waveform is applied to the input of a differentiator, the
output waveform will be a/an …
A DC level.
B inverted triangular waveform.
C first harmonic frequency of the triangular waveform.
D square waveform. (1)
1.10 The basic circuit of a passive RC differentiator is a …
A capacitor in series with the input and a resistor in parallel with the
output.
B resistor in series with the input and a capacitor in parallel with the
output.
C resistor in series with the input and a resistor in parallel with the output.
D capacitor in series with the input and a capacitor in parallel with the
output. (1)
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Electrical Technology: Electronics 5 DBE/2022
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1.11 A/An … circuit is used to clean up an input signal which has been distorted.
A integrator
B differentiator
C Schmitt trigger
D comparator (1)
1.12 In a class C amplifier, the output collector current will flow through the
transistor for … of the input cycle.
A more than 180⁰
B 90⁰
C 360⁰
D less than 180⁰ (1)
1.13 The operation of a relaxation oscillator is based on …
A the charging and discharging of a capacitor.
B a highly selective resonant circuit.
C a very stable supply voltage.
D lower power consumption. (1)
1.14 For an oscillator to maintain oscillation, the gain must be …
A 1.
B less than 1.
C greater than 1.
D equal to β. (1)
1.15 A bipolar junction transistor class B push-pull amplifier with no transformer
coupling uses …
A two NPN transistors.
B two PNP transistors.
C one NPN transistor.
D complementary symmetrical transistors. (1)
[15]
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Electrical Technology: Electronics 6 DBE/2022
SC/NSC
QUESTION 2: OCCUPATIONAL HEALTH AND SAFETY
2.1 Explain the term machinery with reference to the Occupational Health and
Safety Act, 1993 (Act 85 of 1993). (2)
2.2 Explain the term critical incident with regard to emergencies. (2)
2.3 State TWO steps you should take when you discover a fire in an electrical
workshop. (2)
2.4 State the importance of wearing a face mask in the workshop. (2)
2.5 Name TWO environmental considerations when working with chemicals
during the printed circuit board manufacturing process. (2)
[10]
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Electrical Technology: Electronics 7 DBE/2022
SC/NSC
QUESTION 3: RLC CIRCUITS
3.1 Define a phasor diagram with reference to RLC circuits connected across an
alternating voltage supply. (2)
3.2 FIGURE 3.2 below shows an RLC series circuit which consists of a resistor
with a resistance of 10 Ω, an inductor with an inductive reactance of 14 Ω and
a capacitor with a capacitive reactance of 8 Ω, all connected across an
alternating supply of 100 Hz.
R = 10 Ω XL = 14 Ω XC = 8 Ω
150 V 180 V 90 V
100 Hz
FIGURE 3.2: SERIES RLC CIRCUIT
Given:
R = 10 Ω
XC = 8Ω
XL = 14 Ω
VR = 150 V
VL = 180 V
Vc = 90 V
f = 100 Hz
3.2.1 Calculate the total supply voltage applied to the circuit. (3)
3.2.2 Discuss whether the power factor will be leading or lagging. (3)
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Electrical Technology: Electronics 8 DBE/2022
SC/NSC
3.3 Refer to FIGURE 3.3 below and answer the questions that follow.
C
IC = 4 A
L
IL = 6 A
IR = 4 A R
IT
AC
Supply
FIGURE 3.3: PARALLEL RLC CIRCUIT
Given:
Ic = 4A
IL = 6A
IR = 4A
3.3.1 Calculate the total current. (3)
3.3.2 Calculate the phase angle. (3)
3.3.3 Draw the phasor diagram for FIGURE 3.3. (4)
3.3.4 Motivate with a reason if the circuit is predominately capacitive or
inductive. (2)
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Electrical Technology: Electronics 9 DBE/2022
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3.4 Refer to FIGURE 3.4 below and answer the questions that follow.
V = 600 V
R = 2,2 k Ω L = 10 mH XC = 150 Ω
fr = 2,387 kHz
FIGURE 3.4: RESONANT RLC CIRCUIT
3.4.1 Calculate the quality factor of the circuit. (3)
3.4.2 Calculate the bandwidth. (3)
3.4.3 Calculate the value of the capacitor. (3)
3.4.4 Define the term selectivity with reference to resonant circuits. (2)
3.5 Refer to FIGURE 3.5 below and answer the questions that follow.
P
+V
+V
V
V Average
I power
I
00 t 00 t
o 180o 270o o 180
o o
90 360o
90 360
-V -V
(A) (B)
FIGURE 3.5: CURRENT, VOLTAGE AND POWER WAVEFORMS
3.5.1 State with a reason the type of component that produces the
waveform in FIGURE 3.5 (A). (2)
3.5.2 Identify the component across which power is dissipated in
FIGURE 3.5 (B). Motivate your answer. (2)
[35]
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Electrical Technology: Electronics 10 DBE/2022
SC/NSC
QUESTION 4: SEMICONDUCTORS
4.1 Draw a fully labelled IEC symbol of a unijunction transistor. (3)
4.2 Refer to FIGURE 4.2 below and answer the questions that follow.
ID(mA) ID(mA)
(V) -6 + VDS
-5 -4 -3 -2 -1
Transfer characteristic Output characteristic
FIGURE 4.2: TRANSFER CHARACTERISTIC OF JFET
4.2.1 Draw a fully labelled output characteristic curve of the n-channel
junction field-effect transistor (JFET) for the given transfer
characteristic shown in FIGURE 4.2 on the ANSWER SHEET for
QUESTION 4.2.1. (3)
4.2.2 On the ANSWER SHEET for QUESTION 4.2.2, indicate the
pinch-off voltage on the output characteristic curve if
VGS = -1 V. (1)
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Electrical Technology: Electronics 11 DBE/2022
SC/NSC
4.3 Refer to FIGURE 4.3 below and answer the questions that follow.
VDD
R1 RD
C2
Vout
D
C1
Vin G
S RL
R2 RS
0V
FIGURE 4.3: AMPLIFIER CIRCUIT DIAGRAM
4.3.1 Identify the amplifier circuit diagram in FIGURE 4.3. (2)
4.3.2 Describe how the circuit will be able to amplify the input signal as a
linear amplifier. (3)
4.3.3 Complete the input transfer characteristic curve of the circuit
diagram in FIGURE 4.3 by using the information provided on the
ANSWER SHEET for QUESTION 4.3.3. (3)
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Electrical Technology: Electronics 12 DBE/2022
SC/NSC
4.4 Refer to FIGURE 4.4 below and answer the questions that follow.
+ 9V
LED
R1 = 100 kΩ
R2 = 300 Ω
S1
C
B
E
0V
FIGURE 4.4: TRANSISTOR CIRCUIT DIAGRAM
4.4.1 Identify the application of the transistor circuit diagram in
FIGURE 4.4. (1)
4.4.2 Briefly describe the operation of the circuit when the switch is
closed. (3)
4.5 Refer to FIGURE 4.5 below and answer the questions that follow.
R F = 3 kΩ
R IN = 100 Ω + 15 V
_
+ VOUT
0 V - 15 V
FIGURE 4.5: INVERTING OP AMP
4.5.1 State why the circuit is called an inverting op amp. (1)
4.5.2 Explain how the gain of the op amp is controlled. (2)
4.5.3 Calculate the gain of the op amp. (3)
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Electrical Technology: Electronics 13 DBE/2022
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4.6 FIGURE 4.6 below shows the 555 IC. Answer the questions that follow.
0V 1 8 +Vcc
TRIGGER 2 7 DISCHARGE
555 IC
OUTPUT 3 6 THRESHOLD
CONTROL
RESET 4 5
VOLTAGE
FIGURE 4.6: 555 IC PIN LAYOUT
4.6.1 Briefly describe the functions of pin 6 with reference to the 555 IC. (3)
4.6.2 State the supply voltage range at which the 555 IC operates. (2)
4.6.3 Explain the function of the SR flip-flop in the internal circuit of the
555 timer. (2)
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Electrical Technology: Electronics 14 DBE/2022
SC/NSC
4.7 Refer to FIGURE 4.7 below and answer the questions that follow.
Vcc = +5 V to 15 V
R1 R2 8 4
Vout
7 3
555 IC
6
1
2
0 5 1
Trigger
Input C1
C = 0,01 µF
(S1)
0V
FIGURE 4.7: 555 IC MULTIVIBRATOR
4.7.1 Identify the multivibrator in FIGURE 4.7. (1)
4.7.2 Give a brief description of what happens when the push-to-make
switch (S1) is activated. (4)
4.7.3 Draw on the ANSWER SHEET for QUESTION 4.7.3 the voltage
waveform of the capacitor C1 and the output voltage waveform
when the trigger input is pressed. (4)
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Electrical Technology: Electronics 15 DBE/2022
SC/NSC
4.8 Refer to FIGURE 4.8 below which has an output frequency of 1 hertz and
answer the questions that follow.
9V
R1
4 8
7
3
Vout
555 f = 1 Hz
R2 R3
6
2 1 5 LED
C1 C2
0V
FIGURE 4.8: ASTABLE MULTIVIBRATOR
4.8.1 Explain the mode (state) of the LED. (2)
4.8.2 Explain the effect on the LED when:
(a) R2 is halved (1)
(b) The value of C1 is doubled (1)
[45]
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Electrical Technology: Electronics 16 DBE/2022
SC/NSC
QUESTION 5: SWITCHING CIRCUITS
5.1 Name the type of multivibrator that:
5.1.1 Produces one pulse cycle of 'high' and 'low' when a trigger pulse is
applied to its input (1)
5.1.2 Changes state when a trigger pulse is applied and remains in that
state (1)
5.2 Refer to FIGURE 5.2 below and answer the questions that follow.
+9V
R2 R1
10 kΩ 10 kΩ
R3
4 8 470 Ω
7 555 3
6
2
1 5
LED
Set Reset
C1
10 nF
FIGURE 5.2: BI-STABLE MULTIVIBRATOR
5.2.1 Name the function of resistors:
(a) R1 (1)
(b) R3 (1)
5.2.2 Identify the state of the LED when trigger pin 2 is high. (1)
5.2.3 Explain what happens in the circuit when the set switch is pressed. (2)
5.2.4 Explain the purpose of connecting pin 6 to ground. (2)
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Electrical Technology: Electronics 17 DBE/2022
SC/NSC
5.3 FIGURE 5.3 below shows an op amp as a comparator. The resistance of the
LDR increases as the level of light falls.
+V
R1
V Vin 100 kΩ
R3
V in
Vref 1 kΩ
741
t
R2
100 kΩ LED 2
LDR LED 1 white
red
0V
-V
FIGURE 5.3: OP AMP COMPARATOR AS A DARK SENSOR
5.3.1 State the purpose of R2. (1)
5.3.2 Explain how an increase in the level of light affects the voltage on
the non-inverting input. (2)
5.3.3 Explain the operation of the circuit with reference to the voltages on
the input terminals and the output voltage. (3)
5.3.4 Predict the state of LED1 and LED2 when the voltage on the
inverting terminal is higher than the voltage on the non-inverting
terminal. (2)
5.3.5 Draw the output on the ANSWER SHEET for QUESTION 5.3.5. (3)
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Electrical Technology: Electronics 18 DBE/2022
SC/NSC
5.4 Refer to FIGURE 5.4 below and answer the questions that follow.
VIN +10 V
V
0
t VOUT
RF
-10 V 9 kΩ
1V
0
t R1
-1 V
1 kΩ
0V
FIGURE 5.4: SCHMITT TRIGGER
5.4.1 Identify the type of Schmitt trigger circuit. (1)
5.4.2 Determine the value of the output voltage when the voltage on the
non-inverting input is -1 V. (1)
5.4.3 State whether this circuit uses positive or negative feedback. (1)
5.4.4 Explain the operation of the circuit with reference to the input and
trigger voltage levels. (4)
5.4.5 Predict how an increase in the value of R1 will affect the trigger
voltage level. (1)
5.4.6 Draw the output signal on the ANSWER SHEET for
QUESTION 5.4.6. (4)
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Electrical Technology: Electronics 19 DBE/2022
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5.5 Refer to FIGURE 5.5 below and answer the questions that follow.
RF 100 kΩ
C1 R1 10 kΩ
0,4 V
C2 R2 10 kΩ +9 V
0,5 V -
C3 R3 10 kΩ +
0,25 V VOUT
-9 V
0V
FIGURE 5.5: SUMMING AMPLIFIER
5.5.1 The variable resistor RF serves a dual purpose. Name both
purposes. (2)
5.5.2 Calculate the output voltage when the value of RF is set to
78,26 kΩ. (3)
5.5.3 Explain how an increase in the value of RF affects the gain of the
amplifier. (1)
5.5.4 Describe why it is not recommended to increase the value of RF
beyond 78,26 kΩ. (4)
5.5.5 Explain how this limitation can be overcome without changing the
value of any of the resistors. (2)
5.6 Refer to FIGURE 5.6 below and answer the questions that follow.
V R
1 kΩ
Input
VIN VOUT
t
Vsupply C
Output 10 µF
t
FIGURE 5.6: PASSIVE RC INTEGRATOR
5.6.1 Draw the output when the value of C is changed to 1 µF on the
ANSWER SHEET for QUESTION 5.6.1. (3)
5.6.2 Draw the output when the value of C is changed to 100 µF on the
ANSWER SHEET for QUESTION 5.6.2. (3)
[50]
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Electrical Technology: Electronics 20 DBE/2022
SC/NSC
QUESTION 6: AMPLIFIERS
6.1 Describe the term linear amplifier with reference to amplifiers. (2)
6.2 Name ONE consideration when determining the amplifier class. (1)
6.3 Refer to FIGURE 6.3 below and answer the questions that follow.
IC
(mA)
12
10
Q1
8 A IB = 500 µA
6 IB = 400 µA
Q2
4 IB = 300 µA
2 IB = 200 µA
Q3
IB = 100 µA
B
VCE
2 4 6 8 10 12 (V)
FIGURE 6.3: DC LOAD LINE
6.3.1 In which region (A or B) does the saturation point of the biased
transistor occur? (1)
6.3.2 At which Q-point would class AB amplifiers be represented along
the DC load line? (1)
6.3.3 Name ONE condition that affects the quiescent voltages and
quiescent currents at Q3. (1)
6.4 Briefly explain how class B amplifiers operate. (2)
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Electrical Technology: Electronics 21 DBE/2022
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6.5 Refer to FIGURE 6.5 below and answer the questions that follow.
Stage 1 Stage 2 + VCC
R1 R C1 C2 R3 RC2
C3
C1
Q1 Q2
AC RL
Input CE1 CE2
R2 R E1 R4 RE2
0V
FIGURE 6.5: TWO-STAGE RC-COUPLED AMPLIFIER
6.5.1 State the purpose of using multi-stages in amplifiers. (1)
6.5.2 Calculate the total voltage gain in decibel of the circuit diagram
if stage 1 has a voltage gain of 10 and stage 2 has a voltage gain
of 15. (5)
6.5.3 Draw the output waveform across the load on the
ANSWER SHEET for QUESTION 6.5.3. (3)
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Electrical Technology: Electronics 22 DBE/2022
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6.6 Refer to FIGURE 6.6 below and answer the questions that follow.
+ VCC
T1 T2
R1 Matching R3
transformer
Matching
transformer
Q1 Q2
C2
R2 R E1 C1 R4 R E2 C3
0V
FIGURE 6.6: TRANSFORMER COUPLED AMPLIFIER
6.6.1 State the function of capacitor (C2) connected across resistor R4. (2)
6.6.2 Name ONE advantage of a transformer coupled amplifier. (1)
6.6.3 Explain why it is preferable to connect the load via an output
transformer (T2). (2)
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Electrical Technology: Electronics 23 DBE/2022
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6.7 Refer to FIGURE 6.7 below and answer the questions that follow.
+VCC
T2
R1 C1 C2 Output
T1
Q1
Input
R2 C3 R2 CE
0V
FIGURE 6.7: AMPLIFIER CIRCUIT DIAGRAM
6.7.1 Identify the amplifier in FIGURE 6.7. (1)
6.7.2 Describe the basic operation of the amplifier circuit. (2)
6.7.3 Give a reason why capacitor C2 is connected across the secondary
coil of transformer T2. (2)
6.8 The power of an amplifier is 200 mW at a frequency of 20 kHz. When the
frequency increases to 30 kHz, the power decreases to 100 mW. Calculate
the power loss of the system in decibel. (3)
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Electrical Technology: Electronics 24 DBE/2022
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6.9 Refer to FIGURE 6.9 below and answer the questions that follow.
+ VCC
R1 RF choke
C3 C6
C4
Q1
C1 R2
R3
C5
L
0V
C2
FIGURE 6.9: OSCILLATOR CIRCUIT DIAGRAM
6.9.1 Identify the oscillator circuit diagram in FIGURE 6.9. (1)
6.9.2 Briefly describe the function of the:
(a) Amplifier circuit (2)
(b) Tank circuit (2)
6.9.3 Explain why the feedback network (RF choke and C3) is regarded
as a filter. (2)
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6.10 Refer to FIGURE 6.10 of an RC-phase shift oscillator and answer the
questions that follow.
+VCC
RB RC
C5
VOUT
C1 C2 C3
Q1
R1 R2 R3 R4 C4
0V
FIGURE 6.10: RC-PHASE SHIFT OSCILLATOR
6.10.1 State ONE function of R3. (1)
6.10.2 Describe how the RC-phase shift oscillator achieves its phase shift
of 360⁰ during its operation. (4)
6.10.3 Calculate the oscillation frequency of the oscillator circuit if
R1 = R2 = R3 =10 kΩ and C1= C2= C3 = 0,001 µF. (3)
[45]
TOTAL: 200
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FORMULA SHEET
RLC CIRCUITS SEMICONDUCTOR DEVICES
P V I cos θ V R RF
Gain A V OUT F AV 1
XL 2 fL VIN RIN RIN
1 R
XC VOUT VIN F
2 fC R IN
fr
1 OR fr f2 f1 R
2 LC 2 VOUT VIN 1 F
fr R IN
BW OR BW f2 f1
Q SWITCHING CIRCUITS
SERIES R R R
VOUT V1 F V2 F ...VN F
VR I R R1 R2 RN
VL I XL VOUT VOUT
Gain A V
VC I XC VIN V1 V2 ...VN
VT IT IR IC IL VOUT (V1 V2 ...VN )
IT OR
Z AMPLIFIERS
V
Z R 2 X L X C
2
IC C VCC VCE ICRC
RC
VT VR VL VC VT I Z VB VBE VRE
2 2
OR
R VR VOUT
Cos θ OR Cos θ AV
Z VT VIN
XL X C VL VC 1 L I
Q A I OUT
R R VT VT R C IIN
PARALLEL P
A P OUT AP A V A I
VT VR VL VC PIN OR
VT
IR βT = β 1 x β 2 OR A VT A V1 A V2 A V3 ...A Vn
R
VT
IC PIN I2 ZIN POUT I2 Z OUT
XC AND
V OSCILLATION FREQUENCY
IL T 1 1
XL fo OR fo
2 π LC 2 π 6 RC
IT IR IL IC
2 2
GAIN IN DECIBELS
VT I
Z A I 20log10 OUT
IT IIN
I
Cos θ R A V 20log10
VOUT
OR A V 20log 10 A VT
IT VIN
R R POUT P
Q A P 10log10 OR A P 10log10 2
XL X C PIN P1
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Electrical Technology: Electronics DBE/2022
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CENTRE NUMBER:
EXAMINATION NUMBER:
ANSWER SHEET
QUESTION 4: SEMICONDUCTORS
4.2.1 ID(mA) ID(mA)
and
4.2.2
(V) -6 + VDS
-5 -4 -3 -2 -1
Transfer characteristic Output characteristic
Transfer mark to
Transfer mark to
answer book
answer book
MOD
MOD
(4.2.1) (4.2.2)
FIGURE 4.2 (4)
4.3.3
ID(max)
Transfer mark to
ID Q answer book
VGS
MOD
VQ VGS
FIGURE 4.3.3 (3)
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4.7.3
V
Trigger t
input
Capacitor
voltage
t
Transfer mark to
answer book
Output
voltage
MOD
t
FIGURE 4.7.3 (4)
QUESTION 5: SWITCHING CIRCUITS
5.3.5 Vin
V
Vref
Input
t
Vsat
Transfer mark to
answer book
Output
MOD
t
FIGURE 5.3.5 (3)
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5.4.6 +V
Upper trigger
voltage
0
Lower trigger
voltage
-V
+Vsat
0 Transfer mark to
answer book
MOD
-Vsat
FIGURE 5.4.6 (4)
5.6.1 V
Input
t
Vsupply
Transfer mark to
answer book
Output
t MOD
FIGURE 5.6.1 (3)
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5.6.2 V
Input
t
Vsupply
Transfer mark to
answer book
Output
t MOD
FIGURE 5.6.2 (3)
QUESTION 6: AMPLIFIERS
6.5.3
+V
Input 0
t
-V
+V
Output 0
t Transfer mark to
answer book
-V MOD
FIGURE 6.5.3 (3)
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