EENG16000 ELECTRONICS 1 2019
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EENG16000
ELECTRONICS 1
2019
Q1
(a) Sketch the linear equivalent circuits that represent the behaviour of
(i) a non-ideal transconductance amplifier
(ii) a non-ideal transresistance amplifier
In both cases, explain the function of any passive components included in the equivalent circuits and state what their ideal values should be.
(4 marks)
(b) An amplifier operating from a ±18V DC supply provides an output voltage of 25V peak-to-peak
and an output current of 5mA rms to a resistive load when a signal of 1V rms is connected to its input. The input resistance of the amplifier is 10kΩ . A current of 10mA DC is provided by each power supply. Calculate
(i) the voltage and current gains of the amplifier in dB
(ii) the power gain of the amplifier in dB
(iii) the efficiency of the amplifier
(iv) the value of the resistive load connected the output of the amplifier
(6 marks)
(c) The amplifier shown in figure Q1, is based on an op-amp which is characterised by a finite open-loop gain, A.
(i) Derive an expression for the voltage gain of the amplifier G = vO /vI as a function of R1, R2 and A.
(ii) Derive an expression for the input resistance of the amplifier as a function of of R1, R2
and A.
(10 marks)
Figure Q1
Q2
(a) For the circuit in figure Q2a, assuming that the op-amp is ideal in all respects,
(i) Derive an expression for the gain of the circuit vO /vI as a function of frequency.
(ii) Sketch the magnitude of the gain in dB versus 业 using a Bode plot. Use the following
values for the passive components: C = 1uF, R = 10kΩ and RF = 100kΩ . Label the axes carefully so that the slope of any lines may be clearly seen.
(14 marks)
(b) For the schematic in figure Q2b, derive an expression for vO (t) as a function of vI (t). Note
that both vO and vI are functions of time in this case. Assume that the op-amp is ideal in all respects.
(6 marks)
Figure Q2a
Figure Q2b
Q3
(a) For the circuit in figure Q3. Derive an expression for the output voltage vO as a function of the
input voltage vI
(8 marks)
(b) (i) Describe the differences between an Instrumentation Amplifier and a Difference
Amplifier.
(ii) Explain the term Common Mode Rejection Ratio of an amplifier and describe briefly the
circumstances where this parameter is important in modelling the behaviour of a circuit.
(iii) Give two examples of applications of Instrumentation or Difference Amplifiers.
(7 marks)
(c) (i) Explain the terms input offset voltage and input bias currents and draw an op-amp circuit model which takes these parameters into account.
(ii) Explain the difference between inverting integrators with and without feedback in
practical circuits and how the non-ideal aspects of operational amplifiers affect their operation.
(5 marks)
Figure Q3
Q4
(a) Sketch the I-V characteristic of
(i) A standard diode
(ii) A Zener diode
In your sketch, clearly label the different operating regions. Describe how these devices differ and give an example of a typical application for each type.
(6 marks)
(b) Figure Q4(a) shows a series combination of a diode, resistor and an arbitrary voltage source.
The diode characteristic is shown in figure Q4(b). The source voltage vS is the waveform shown in figure Q4(c). The value of the resistor R is 100Ω .
(i) Sketch the waveform of the voltage vR across the resistor. Clearly mark its peak value on the vertical axis and the points at which conduction starts and ends on the horizontal axis.
(ii) Calculate the average value of vR and the average value of iD
(10 marks)
(c) (i) Draw the circuit diagram of an AC-DC converter which employs a full-wave rectifier and a transformer.
(ii) Explain the function of Zener diodes in AC/DC converters.
(4 marks)
Figure Q4
2022-08-08