Download 12. Modelling of diodes and bipolar transistors

12. MODELLING OF DIODES AND BIPOLAR
TRANSISTORS
12.1. Objective of the test
Learn how it is possible to simulate operation of electronic
elements. Become acquainted with major parameters of diodes and
bipolar transistors and examine their meaning.
12.2. Using modelling software
During this laboratory test use the software package Electronics
Workbench which is much like a real electronics workbench. The
large central area of a display is the workspace where you build and
test a circuit. Beside the workspace is a parts bin. At the top of the
display you can find menus, test instrument icons and the power
switch for activating the circuit.
To build and test a circuit:
1. Drag components from the parts bin.
2. Place them on the workspace.
3. Wire the components together.
4. Set component values or models.
5. Attach test instruments.
6. Activate the circuit.
Main instruments:
Multimeter. Use the multimeter to measure voltage, current,
resistance or decibel loss between two test points in a circuit.
Function generator. The function generator is a voltage source
that supplies analog signals in the form of sine, square and triangular
waves. You can adjust the signal frequency, duty cycle, amplitude and
DC offset.
Oscilloscope. The oscilloscope displays the magnitude and
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frequency variations of electronic signals. It has two input terminals,
channel A and channel B, so two different signals can be displayed
simultaneously.
12.3. Preparing for the test:
Using lecture-notes and referenced literature [2, p. 3–19],
consider diodes and bipolar transistors classification, principles
of operation, properties and major parameters.
 Consider section “12.4. In laboratory” of this test.
 Prepare to answer the questions:
1. What types of diodes are used at high frequency? Why?
2. Write expression of the static resistance of a diode.
3. Write expression of the dynamic resistance of a diode.
4. Explain the meaning of the turn-off time of a junction diode.
5. How can the turn-off time be reduced?
6. What phenomena limit the frequency range of a bipolar transistor?
7. What factors have severe limitation on the bipolar transistor
frequency response?
8. How can the frequency range of a bipolar transistor be increased?
9. Sketch the -type model of a BJT. Comment on its elements.
10. Define f  , f , fT . How are these parameters related to each
other?
11. Describe the peculiarities of drift transistors.
12. Explain the advantages of epitaxial transistors.

1.
2.
3.
12.4. In laboratory:
Answer the test question.
Familiarize with the modelling software.
Measure volt-ampere characteristics (VACs) of two different
diodes.
To this end create the simulation circuit shown in Fig 12.1. Fill
Table 12.1 and according to it draw VACs. Examine parameters
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Fig 12.1. Measurement circuit
of the diodes. Determine which parameters impact frequency
characteristics of the diodes.
Table 12.1. Measurement results
Diode 1N4001
Current
Voltage
I
U
…
4.
5.
6.
Diode MBR4020
Current
Voltage
I
U
…
…
…
Model amplification of a circuit with a bipolar transistor.
To this end create the simulation circuit shown in Fig 12.2. Using
multimeter and oscilloscope measure voltages at input and output
of the circuit. The output of the function generator must be sine
wave with frequency 100 MHz and amplitude of 100 mV.
Repeat simulation using three different bipolar transistors (low
frequency, medium frequency and high frequency). Fill
Table 12.2. Examine parameters of bipolar transistors. Determine
which parameters impact bipolar transistor frequency characteristics.
Examine the results. Repeat the simulation if it is necessary.
Prepare the report.
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Fig 12.1. Measurement circuit
Table 12.2. Measurement results
Transistor
Input
voltage
UIN / mV
Output
voltage
UOUT / V
Amplification
UOUT/UIN
Amplification
in decibels:
20lg(UOUT/UIN)
2N2714
2N2369
2N3600
1.
2.
3.
4.
5.
12.5. Contents of the report
Objectives.
Characteristic of the simulated circuits.
VACs of the diodes.
Results of measurements and calculations of amplification.
Conclusions (comments on parameters impact on characteristics of diode and bipolar transistor).
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