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UNIVERSITY OF OSLO
FACULTY OF MATHEMATICS AND NATURAL SCIENCES
Exam in
: FYS1210 Electronics with projects
Day of exam : Tuesday 2th of June 2015
Exam hours : 09:00 -12:00 ( 3 hours )
This examination consists of 4 pages (+ 3 sheets of log paper)
Appendices : 3 sheets of log-paper
Permitted materials: Small calculator, Text book
Robert T. Paynter & B.J.Toby Boydell "Electronics Technology Fundamentals".
Make sure that your copy of the examination paper is complete before answering.
Task 1: Frequency Filter
The frequency filter shown in figure 1 has the following parameters:
C1=1nF, C2=100nF R1=10 kΩ R2=10 kΩ
1a) What kind of filter is this? What is the
cutoff frequency in point A (The node
between R1 and R2), and how large is the
phase difference at this frequency?
1b) What kind of filter will we get by
switching the positions of the capacitors and
resistors? (R1 and R2 exchange places with
C1 and C2, respectively). Elaborate on your
answer.
1c) Looking at Figure 1, we now change the position of R1 and C1 with each other, creating a
bandpass filter. What is the phase shift for intermediate frequencies of this filter?
1d) Calculate the bandwidth of the bandpass filter in task C.
1e) Use the provided logarithm paper and draw the frequency characteristics of the
bandpass filter. Write your candidate number on the sheet. The sheet shall be delivered
with the rest of your examination.
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Exam FYS1210 – 2015s
Task 2: Operation Amplifier
2a) You shall now make a circuit including an operation amplifier, with a gain Av = 100,
where the output signal is in-phase with the input signal. Draw the circuit and assign
component values. Also, write the mathematical expression for the gain of this type of
amplifier. What can you say about the input impedance of such an amplifier?
2b) The operation amplifier has a Gain Bandwidth Product (GBW) = 1MHz, unity gain. If the
voltage gain is Av = 100, what is the resulting cutoff frequency of the amplifier?
2c) Can this amplifier be used in a Hi-Fi system?
(Hi-Fi requires linear phase response in the frequency range 20 Hz – 20 kHz). Provide a short
elaboration on your answer.
2d) You have multiple operation amplifiers at your disposal, all with a GBW = 1MHz. You
shall now construct a new circuit, with voltage gain = 30, and inverted output signal. Cutoff
frequency of the circuit should be at 100 kHz. Draw the circuit and provide the necessary
component parameters.
2e) The amplifier in task 2a has a slew rate of 0.5V/ μsec. What is the highest signal
frequency (sine wave) that the amplifier can recreate without distortion, if the signal has an
amplitude Vp = 4 Volt?
We send in a square wave, with amplitude of 4 volts, lasting 4 μsec. Draw the resulting
output signal.
Task 3:
Sensors / ADC / DAC
3a) In the lectures, we have talked about a LVDT position sensor (Linear Variable Differential
Transformer). Draw a sketch of such a sensor and explain in short how it works. Name an
application area of such a sensor.
3b) Name two techniques of analogue-to-digital conversion, and list advantages and
disadvantages of the two techniques.
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Exam FYS1210 – 2015s
3c) There are multiple ways of converting a signal from digital to analogue form. How can
this be done using a circuit incorporating an operation amplifier? Draw the circuit and
explain how it works.
Task 4: Transistor Amplifier
Figure 4 shows a typical transistor amplifier. To secure the circuit against wrongful wiring of
the battery, we have inserted a silicon diode D1 (1N4002) in the supply line. The transistor
has a current gain β = 200. All questions in task 4 are based on the circuit shown in Figure 4.
The following voltage measurements are given:
Collector – emitter voltage VCE = 4 volt. Emitter voltage VE = 2,3 volt.
Battery voltage V1 = 12 volt
4a) Sketch the Thevenin-equivalent of the forward biasing of the base, and calculate the
Thevenin-voltage (VTH) and the Thevenin-resistance (RTH)
4b) Calculate the base current IB.
4c) Calculate the collector current IC.
4d) Calculate the transconductance gm of the transistor.
4e) Draw the small signal equivalent of the circuit, for high frequencies.
4f) Calculate the voltage gain of intermediate frequencies, with and without the capacitor
(C4) over the emitter resistor (R5).
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Exam FYS1210 – 2015s
4g) Describe in short what you understand by Miller effect. How does this affect the
frequency response of an amplifier?
4h) Figure 4B shows 2 simulations from PSpice – with and without the emitter capacitor.
Using the plots shown below, determine (approximately) the cutoff frequencies, and explain
in short terms why the frequency characteristics change by removing the capacitor.
Simulation WITH emitter capacitor
FIGURE 4B. Above is a simulation with emitter capacitor, below a simulation without
the capacitor. X-axis shows frequency (Hz), Y-axis shows voltage gain (dB).
Simulation WITHOUT emitter capacitor
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