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EMT 212
Analog Electronics II
Tutorial 3
Question 1
22k
1k
2k
B
A
0.2uF
D
C
0.02uF
0.002uF
200pF
+15V
+
Vout
_
B
A
C
-15V
D
22k
0.2uF
0.02uF
0.002uF
10k
Rlamp
200pF
2k
Figure 1(a): Wien bridge oscillator
Rlamp
750

500 
350 
300 
2
3
4 Vlamp(rms)(V)
Figure 1 (b): Lamp characteristic
The Wien bridge oscillator shown in Figure 1(a) above uses lamp with characteristic shown in Figure
1(b). Answer the following questions:
a. Determine the output voltage.
b. Position D in Figure 1(a) is the highest frequency range of the oscillator. We can vary the
frequency using ganged rheostats. What are the minimum and maximum frequencies of
oscillation of this range?
c. Determine the minimum and maximum frequency of oscillation for each position of the ganged
switch.
d. Determine feedback resistor to produce output voltage of 6 Vrms?
e. The cut off frequency of the amplifier with negative feedback is at least 1 decade above the
highest frequency of oscillation. What is the cut off frequency?
Question 2
D1
D2
6.8V
6.8V
47k
100k
Vout
_
1k
1k
R2
0.015uF
0.015uF
+
Figure 2
Answer the question below based on Figure 2.
a. Determine the necessary value of R2, so that the circuit will oscillate. Neglect the forward
resistance oh the zener diodes.
b. Explain the purpose of R3
Question 3
Rf
0.022uF
Ri
0.022uF
0.022uF
_
+
4.7k
4.7k
Figure 3: Phase shift oscillator
Answer the following question based on Figure 3. Determine:
a. The value of Rf necessary for the circuit to operate as an oscillator
b. The frequency of oscillation
Question 4
Av
Vf
Vout
β
Tank Circuit
Figure 1
Figure 2
Figure 1 shows closed loop connection between amplifier and feedback circuit/tank circuit. Colpitts and
Hartley oscillators can be configured depending on the tank circuit used in circuitry shown in Figure 2.
Answer the questions below based on Figure 1 and Figure 2.
a) Derive a formula to calculate resonant frequency of Colpitts and Hartley oscillators.
b) Derive a formula to determine feedback attenuation factor, β for Colpitts and Hartley oscillators.
Show what the voltage gains are, Av for Colpitts and Hartley circuits.
c) A Colpitts oscillator has the following parameters. Determine the feedback attenuation factor, β
and voltage gain, Av.
Resonant frequency, fr = 1.5MHz
C2 =10nF
L = 1.6mH
d) A Hartley oscillator has the following parameters. Determine the feedback attenuation factor, β
, voltage gain, Av and value of capacitor, C.
Resonant frequency, fr = 1.5MHz
L1 = 2µH
L2 = 3µH
Question 5
Refer to Figure 5b. At t<0, the capacitor is fully discharged. At t=0, the switch will be closed. Assume the
forward voltage, VF for the Programmable Unijunction Transistor, PUT is 1V and the 0.7V drop across it is
ignored.
+12 V
R4 = 100k
R5 = 47k
C1 = 0.0022µF
+12 V
R3 = 100k
t=0
+15V
_
Vin
R1= 100k
Vout
+
R2 = 22k
-15V
Figure 5
(i) Calculate the minimum voltage, Vmin for the circuit.
(ii) Calculate Vin.
(iii) Determine the period of the generated output waveform.
(iv) Sketch the output waveform generated by the circuit for at least the first 2 period. Note that the
capacitor is fully discharge at t<0 and the switch is closed at t=0. Label your VF, Vmin and the stable
period of the waveform.
(v) By using the same R5 value, modify the circuit so that the peak-to-peak output voltage is 4V.
Question 6
Design a square wave oscillator that has the following criteria:
Square wave
f = 7.123 kHz
tH = 32.6 µs
% tH = 23.25%
Show your circuit connection.
(Hint: use easy-to-get F unit capacitor)