EENG16000 ELECTRONICS 1 2018
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EENG16000
ELECTRONICS 1
2018
Q1
(a) Sketch the linear equivalent circuits that represent the behaviour of
(i) a non-ideal current 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 ±9V provides an output voltage of 4V peak and an output current
of 14mA rms to a resistive load when a signal of 1V rms is connected to its input. The current drawn by the input port of the amplifier is 1mA peak to peak. A current of 15mA 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 input resistance of the amplifier
(v) the value of the resistive load connected the output of the amplifier
(8 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 vO /vI as a function of R1, R2 and A.
(ii) State what the relationship between R1, R2 and A should be in order to minimise the
effect of a finite open-loop gain.
(8 marks)
Figure Q 1
Q2
(a) For the circuit in figure Q2, 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 = 10nF, R = 10kΩ and RF = 100kΩ . Label the axes carefully so that the slope of any lines may be clearly seen.
(15 marks)
(b) Replace resistor R with a short circuit in the schematic in figure Q2 and 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.
(5 marks)
Figure Q 2
Q3
(a) For the circuit in figure Q3
(i) Derive an expression for the output voltage vO as a function of the input voltages v1, v2, v3 and of the resistor values. The op-amp may be assumed ideal in all respects.
(ii) Suggest a practical application.
(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.
(6 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 how bias currents may cause the output of an inverting integrator to drift to the
power supply rails.
(6 marks)
Figure Q 3
Q4
(a) Sketch the I-V characteristic of
(i) Standard diodes
(ii) Zener diodes
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 150Ω .
(i) Sketch the waveform for the voltage across the resistor vR and clearly mark its peak value.
(ii) Calculate the average and rms values of vR
(iii) Calculate the average and rms values of iD
(8 marks)
(c) (i) Draw the circuit diagram of an AC-DC converter which employs a full-wave rectifier using four diodes and a transformer.
(ii) Draw the circuit diagram of an AC-DC converter which employs full-wave rectifier using
two diodes and a centre-tap transformer.
(6 marks)
Figure Q 4
2022-08-08