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Grades Evaluation
1st Half of the semester
EEE 2103: • (5) Attendance – 10%
40% of
Electronic Devices •
•
(OBE) Assignment – 20%
Quizzes – 30%
semester’s
-Ebad Zahir weight
• Midterm – 40%
AMERICAN INTERNATIONAL UNIVERSITY-
BANGLADESH (AIUB)
2nd Half of the semester
Faculty of Engineering
• (5) Attendance – 10%
Department of Electrical and Electronic Engineering
• Quizzes – 50% 60% of
Undergraduate Program
semester’s
• Final – 40% weight
.
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WEEK Sunday Tuesday TOPIC
#10 27th April 29th April
BJT AC
#11 4th May 6th May
13th May
#12 Buddha Purnima
Calendar
17th May (online)
FET DC Topic – 4
18th May
post- #13
Quiz-3
20th May
BJT AC Analysis
midterm #14 25th May 27th May
Lecture: Week-10 and Week-11
3rd June FET AC
#15 1st June
Quiz-4
#16 Eid Holiday Eid Holiday
#17 FINAL EXAM (June 16)
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Chapter Objectives Review of ACTIVE CIRCUITS
• Become familiar with the re model for the BJT transistor.
• Learn to use the equivalent model to find the important ac
parameters for an amplifier.
• Understand the effects of a source resistance and load resistor
on the overall gain and characteristics of an amplifier.
• Become aware of the general ac characteristics of a variety of
important BJT configurations.
• Begin to understand the advantages associated with the two-
port systems approach to single- and multistage amplifiers.
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• Turning off the independent source affects the
dependent source. RECAP: Dynamic Resistance
• For AC, the varying
input voltage/current
will have an
instantaneous or
dynamic relationship.
• Thus the specific
changes in current and
voltage is obtained
using equation:
rd = ∆VD/ ∆ID
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The base to emitter diode provides an effective resistance at the
emitter, even when it is grounded. This effective resistance is in RECAP: Problem from previous lecture
series with the emitter.
26mV
re
IE
10mV 1.6V
-1.7V
-10mV
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BJT: small signal analysis
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II IO
VI VO
ZI ZO BJT – small signal analysis
• In a linear amplifier, the principle of superposition applies
• The response of the transistor amplifier excited by multiple
independent sources is the sum of the responses of the
circuit to each of the input signals alone.
• So Total Response = DC Response + AC Response
• Both DC and AC analysis can be done separately
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• Magnitude of the AC signal applied for
amplification must be small so that:
ib • The transistor operates in the
linear region for the whole cycle
of input.
0 • The transistor is never driven
+ into saturation or cut-off region
• Then the transistor will operate as a
IB linear amplifier since iC=iB holds in the
active region.
Ib
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BJT TRANSISTOR MODELING
• For finding AC response of a BJT amplifier
• The AC equivalent circuit of the amplifier is determined.
• The transistor is replaced by its model
• A model is a combination of circuit elements,
properly chosen, that best approximates the actual
behavior of a semiconductor device under specific
operating conditions.
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re model for common emitter
Transistor Model
r model
e hybrid model
re = Dynamic Resistance
Fails to account for Limited to specified
the output impedance operating condition
and feedback effect in order to obtain
from output to input accurate result
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re model for common base re model for common collector
• For the CC configuration, the model defined for
the common-emitter configuration is normally
applied rather than defining a model for the
common-collector configuration.
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AC Equivalent Circuit
• AC Equivalent Circuit is obtained by:
1. Setting all DC sources to 0 and replacing them by a
short circuit equivalent
2. Replacing all capacitors by a short circuit equivalent
3. Removing all elements bypassed by the short circuit
equivalents introduced in the previous two steps.
Basic BJT Amplifier AC Equivalent Circuit
4. Redrawing the network in a more convenient and
logical form
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II IO
VI
ZI ZO V O
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EMITTER-FOLLOWER
CONFIGURATION
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Impedance Calculations
COMMON BASE
CONFIGURATION
Gain
Calculations
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Impedance Calculations EFFECT OF RL AND RS
• The loaded voltage gain of an amplifier is always less than the no-load gain.
Gain Calculations • For a particular design, the larger the level of R L , the greater is the level of ac gain.
• For a particular amplifier, the smaller the internal resistance of the signal source, the
• greater is the overall gain.
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Cascaded Systems
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Example
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