ELEC301-电学代写
时间:2023-02-27
ELEC301是一门留学生电路分析的课程,旨在介绍基本电路分析方法和技术。该课程将涵盖电路元件、电路分析技术、交流电路分析等主题,帮助学生理解电路的基本原理,并掌握常见的电路分析技术和工具。通过该课程的学习,学生将具备设计和分析电路的能力。
Electrical and Computer Engineering — ELEC 301
MINI PROJECT 2
BIASSING AND THE COMMON EMITTER AND COMMON BASE AMPLIFIERS
Objectives
To develop familiarity with the transistor’s hybrid-ð model and issues surrounding the biassing of
transistors as well as to analyse and measure the characteristics of an important transistor amplifier
using 3 commonly available transistors.
Introduction
The bipolar junction transistor can be modelled for small signal operation using the hybrid-ð model,
shown in Figure 2.1. Under the assumption of small signals, the transistor is assumed to work in its
active region. Large signals can cause the transistor to enter the saturation or cut-off modes, where the
hybrid-ð model no longer describes the circuit’s operation.
In this mini project, we examine two basic single transistor amplifier circuits, the common emitter and
common base amplifiers. These amplifiers are shown in figures 2.2 and 2.3, respectively.
This project consists of three parts. The transistors that you will be using/considering in your designs
are the 2N2222A, 2N3904, and 2N4401. The data sheets for these transistors may be obtained from the
manufacturers’ web sites (e.g., the 2N3904 and 2N4401 data sheets can be downloaded from the
Fairchild Semiconductor web site) or otherwise found on the web.
References:
1) ELEC 301 Course Notes.
2) Standard Resistor and Capacitor Values list that can be found in the Other Mini Project Related
Handouts module on the course’s CANVAS web site.
3) A. Sedra and K. Smith, "Microelectronic Circuits," 5th (or higher) Ed., Oxford University Press,
New York.
©Nicolas A. F. Jaeger. Not to be copied, used, or revised without explicit written
permission from the copyright owner. Page 1 of 7
Figure 2.2. The Common-Emitter Amplifier.
Figure 2.1. The Hybrid-ð Transistor Model.
©Nicolas A. F. Jaeger. Not to be copied, used, or revised without explicit written
permission from the copyright owner. Page 2 of 7
Figure 2.3. The Common-Base Amplifier.
©Nicolas A. F. Jaeger. Not to be copied, used, or revised without explicit written
permission from the copyright owner. Page 3 of 7
Background
The hybrid-ð model contains five elements: rð, cð, cì, gm and ro (rx and rì have been ignored). You can
also ignore the small-signal capacitances, cð and cì, at low and mid-band frequencies. The other model
element values are either calculated based on the bias conditions (e.g., gm) or can be obtained from the
“h-parameters”. The h-parameter values may be obtained from the data sheets provided by the
transistor’s manufacturer and may depend on the bias point. For example, gm = IC/VT, where IC is the
collector bias current and VT is the thermal equivalent of voltage given by VT = kT/q, where k is
Boltzmann's constant, T is the temperature in degrees Kelvin, and q is the charge on an electron in
Coulombs. Also, rð is given by rð = â/gm, where â is the common-emitter current gain of the transistor.
Here we should note that, by definition, â at d.c. is the same as the h-parameter hFE. hFE is available in
transistor data sheets and is given for various bias points (often it is also plotted as a function of the bias
point).
There are three main configurations in which single transistors may be connected to amplify signals.
The convention is to name each configuration after the node that is shunted to the common voltage at
mid band, i.e., to VCC or ground. The three configurations are the common-emitter (CE), the
common-base (CB), and the common-collector amplifiers (CC); the collector amplifier is not covered
in this mini project.
In the following sections, you will design bias networks for the common emitter amplifier and you will
characterize the response of each type of amplifier.
©Nicolas A. F. Jaeger. Not to be copied, used, or revised without explicit written
permission from the copyright owner. Page 4 of 7
Part 1
a) Download the data sheet for the 2N2222A from the web. Find the values of the small signal
parameters hfe, hie, and hoe for VCE = 10V, IC = 1 mA, f = 1kHz, and T = 25oC (you may have to
look at more than 1 datasheet to find all of these). The “h-parameter model” is another model
for the BJT commonly used for low frequency analysis. These “h-parameters” correspond to
the small signal parameters â, rð, and ro in the hybrid-ð model, respectively, and give us the
small-signal parameters of the hybrid-ð model at specific bias points (in your hybrid-ð model,
you may use hFE for hfe).
b) Using your simulation software, obtain plots for i) IB vs VBE, ii) IC vs VCE with IB as the variable
parameter, and iii) IC vs VCE with VBE as the variable parameter for the 2N2222A transistor and
using these plots calculate â, rð, gm, and ro for VCE = 5V and IC = 1 mA and estimate VA (the
Early voltage). In your report, compare these “measured” (calculated from the curves) values
with those given in the data sheet.
c) Figure 2.4 shows a simple bias network for an npn transistor amplifier (works for both the CE
and CB amplifiers). With proper selection of the values of RB1, RB2, RC, and RE we can bias the
transistor in its active region. Use VCC = 15 V and IC = 1 mA in the following.
i) First use the “measured” (calculated from the curves) parameters, from part b) above, for
a 2N2222A transistor to bias the circuit for a value of VCE of 4V or less and for RE =
RC/2 (i.e., do not use the 1/3 rule here) and measure the d.c. operating point.
ii) Then use the 1/3 rule to bias the circuit and measure the d.c. operating point.
iii) Now, choose the closest commonly available resistors to those that you calculated using
the 1/3rd rule and place them in your circuit1 and measure the d.c. operating point.
iv) In your report, compare the d.c. operating point values that you obtained in parts i), ii),
and iii) above and comment on any observations that you made.
d) Use the circuit that you obtained for part c-iii) and replace the 2N2222A with the 2N3904 and
the 2N4401 transistors and compare the d.c. operating points that you obtained for the three
transistors.
Figure 2.4
1Only use component values listed in the Standard Resistor and Capacitor Values list that can be
found in the Other Mini Project Related Handouts module on the course’s CANVAS web site.
©Nicolas A. F. Jaeger. Not to be copied, used, or revised without explicit written
permission from the copyright owner. Page 5 of 7
Part 2
Using the closest commonly available resistors to those that you calculated using the 1/3rd rule, and
assuming that you have been given three 10uF capacitors for the coupling and by-pass capacitors,
layout the Common Emitter amplifier in your simulation software, using a 2N3904 transistor, a 50Ù
source resistance, and a load resistor RL = RC, and do the following:
a) Plot the Bode plots for magnitude and phase for a sufficient bandwidth so that you can identify
all of the poles (both low frequency and high frequency) and all of the low frequency zeros and
compare your estimates of the locations of the poles and zeros with your calculated locations2.
Then, repeat this for the 2N4401 transistor.
b) Using the Bode plot, pick a mid band frequency. Using this frequency, adjust the amplitude of
the input signal to your amplifier until you feel that the output signal, viewed in the time
domain, is becoming non-linear (you can vary the amplitude of the input signal and plot the
voltage transfer curve, amplitude of vo vs vs). Then, repeat this for the 2N4401 transistor.
c) Measure the input impedance of your amplifier at mid band (include everything other than the
50Ù source resistance) and compare this with the input impedance that you calculate. Then,
repeat this for the 2N4401 transistor.
d) Measure the output impedance of your amplifier at mid band (keep the 50Ù source resistance in
the circuit when you measure the output impedance) and compare this with the output
impedance that you calculate. Then, repeat this for the 2N4401 transistor.
e) Using your results from part a) above, select the transistor, either the 2N3904 or the 2N4401,
that you feel gives the best performance (justify your choice in your report).
Part 3
Repeat Part 2 sections a), b), c), and d) above for the Common Base amplifier for the 2N2222A
transistor only.
___________________
2cð and cì can be approximated using the SPICE model parameters (see your simulation
software to obtain these parameters):
and
©Nicolas A. F. Jaeger. Not to be copied, used, or revised without explicit written
permission from the copyright owner. Page 6 of 7
Report — (i) The report for this project should document the circuits that have been “built” and
“tested.” For each circuit, tabulate the calculated and simulated values. Discuss any observations that
you made. You should present your calculations and/or data in the order that it was requested in this
project sheet. In other words, present the calculations/data for Part 1a followed by the calculations/data
for Part 1b, etc. The discussion for each part should be included following the calculations/data for that
part, i.e., your discussion for Part 1 should come before you present your calculations/data for Part 2.
(ii) Your report should adhere to the Criteria (Instructions) for Uploaded Mini Projects that can be
found in the Other Mini Project Related Handouts module on the course’s CANVAS web site.
©Nicolas A. F. Jaeger. Not to be copied, used, or revised without explicit written
permission from the copyright owner. Page 7 of 7


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