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ECE312_lec04
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Ahmad El-Banna
October 28, 2014
Education
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780
ECE312_lec04
3rd Year, Faculty of Eng. at Shoubra
lec#4, Electronic Circuits (A)
Ahmad El-Banna
October 28, 2014
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Transcript
Lecture #4 BJT Modeling and r e Transistor Model (small
signal analysis) Instructor: Dr. Ahmad El-Banna Benha University Faculty of Engineering at Shoubra October 2014 ECE-312 Electronic Circuits (A) © Ahmad El-Banna
Remember ! Lectures List 2 ECE-312 , Lec#4 , Oct
2014 Week#1 • Lec#1: Introduction and Basic Concepts Week#2 • Lec#2: BJT Review • Lec#3: BJT Biasing Circuits Week#3 • Lec#4: BJT Modeling and re Transistor Model • Lec#5: Hybrid Equivalent Model Week#4 • Lec#6: BJT Small-Signal Analysis • Lec#7: Systems Approach Week#5 • Lec#8: General Frequency Considerations • Lec#9: BJT Low Frequency Response Week#6 • Lec#10: BJT High Frequency Response • Lec#11: Multistage Frequency Effects and Square-Wave Testing © Ahmad El-Banna
Remember ! Lectures List 3 ECE-312 , Lec#4 , Oct
2014 Week#1 • Lec#1: Introduction and Basic Concepts Week#2 • Lec#2: BJT Review • Lec#3: BJT Biasing Circuits Week#3 • Lec#4: BJT Modeling and re Transistor Model • Lec#5: Hybrid Equivalent Model Week#4 • Lec#6: BJT Small-Signal Analysis • Lec#7: Systems Approach Week#5 • Lec#6: General Frequency Considerations • Lec#7: BJT Low Frequency Response Week#6 • Lec#8: BJT High Frequency Response • Lec#9: Multistage Frequency Effects and Square-Wave Testing © Ahmad El-Banna Merged in two lectures only
Agenda Amplification in the AC Domain BJT transistor Modeling The
re Transistor Model (small signal analysis) Effect of RL and Rs (System approach) Determining the Current Gain Summary Table 4 ECE-312 , Lec#4 , Oct 2014 © Ahmad El-Banna
AMPLIFICATION IN THE AC DOMAIN 5 ECE-312 , Lec#4 ,
Oct 2014 © Ahmad El-Banna
Amplification in the AC Domain 6 ECE-312 , Lec#4 ,
Oct 2014 © Ahmad El-Banna • The superposition theorem is applicable for the analysis and design of the dc and ac components of a BJT network, permitting the separation of the analysis of the dc and ac responses of the system.
BJT TRANSISTOR MODELING 7 ECE-312 , Lec#4 , Oct 2014
© Ahmad El-Banna
BJT Transistor Modeling 8 ECE-312 , Lec#4 , Oct 2014
© Ahmad El-Banna • A model is a combination of circuit elements, properly chosen, that best approximates the actual behavior of a semiconductor device under specific operating conditions. Ac analysis • Defining the important parameters of any system.
BJT Transistor Modeling 9 ECE-312 , Lec#4 , Oct 2014
© Ahmad El-Banna • the ac equivalent of a transistor network is obtained by: 1. Setting all dc sources to zero 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 by steps 1 and 2 4. Redrawing the network in a more convenient and logical form
THE r e TRANSISTOR MODEL • Common Emitter Configuration •
Common Base Configuration • Common Collector Configuration • re Model in Different Bias Circuits 10 ECE-312 , Lec#4 , Oct 2014 © Ahmad El-Banna
The r e Transistor Model (CE) 11 ECE-312 , Lec#4
, Oct 2014 © Ahmad El-Banna
The r e Transistor Model (CB) 12 ECE-312 , Lec#4
, Oct 2014 © Ahmad El-Banna
The r e Transistor Model (CC) 13 ECE-312 , Lec#4
, Oct 2014 • For the common-collector configuration, the model defined for the common-emitter configuration of is normally applied rather than defining a model for the common-collector configuration. • The dc analysis of npn and pnp configurations is quite different in the sense that the currents will have opposite directions and the voltages opposite polarities. • However, for an ac analysis where the signal will progress between positive and negative values, the ac equivalent circuit will be the same. npn versus pnp © Ahmad El-Banna
C.E. Fixed Bias Configuration 14 ECE-312 , Lec#4 , Oct
2014 © Ahmad El-Banna
Voltage-Divider Bias 15 ECE-312 , Lec#4 , Oct 2014 ©
Ahmad El-Banna
C.E. Emitter Bias Configuration 16 ECE-312 , Lec#4 , Oct
2014 © Ahmad El-Banna
C.E. Emitter Bias Configuration.. 17 ECE-312 , Lec#4 , Oct
2014 Same as CE fixed bias config. © Ahmad El-Banna
Emitter Follower Configuration 18 ECE-312 , Lec#4 , Oct 2014
© Ahmad El-Banna
Emitter Follower Configuration.. 19 ECE-312 , Lec#4 , Oct 2014
© Ahmad El-Banna
Common-Base Configuration 20 ECE-312 , Lec#4 , Oct 2014 ©
Ahmad El-Banna
Collector-Feedback Configuration 21 ECE-312 , Lec#4 , Oct 2014 ©
Ahmad El-Banna
Collector-Feedback Configuration.. 22 ECE-312 , Lec#4 , Oct 2014 ©
Ahmad El-Banna
Collector DC Feedback Configuration 23 ECE-312 , Lec#4 , Oct
2014 © Ahmad El-Banna
EFFECT OF R L AND R S (SYSTEM APPROACH) 24
ECE-312 , Lec#4 , Oct 2014 © Ahmad El-Banna
Effect of R L and R s 25 ECE-312 ,
Lec#4 , Oct 2014 © Ahmad El-Banna • The loaded voltage gain of an amplifier is always less than the no-load gain. • The gain obtained with a source resistance in place will always be less than that obtained under loaded or unloaded conditions due to the drop in applied voltage across the source resistance. • For the same configuration AvNL >AvL > Avs . • 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. • For any network that have coupling capacitors, the source and load resistance do not affect the dc biasing levels.
Effect of R L and R s .. 26 ECE-312
, Lec#4 , Oct 2014 Voltage-divider ct. Emitter- Follower Ct. © Ahmad El-Banna
DETERMINING THE CURRENT GAIN 27 ECE-312 , Lec#4 , Oct
2014 © Ahmad El-Banna
Determining the Current gain 28 ECE-312 , Lec#4 , Oct
2014 © Ahmad El-Banna • For each transistor configuration, the current gain can be determined directly from the voltage gain, the defined load, and the input impedance.
SUMMARY TABLE 29 ECE-312 , Lec#4 , Oct 2014 ©
Ahmad El-Banna
30 ECE-312 , Lec#4 , Oct 2014 © Ahmad El-Banna
31 ECE-312 , Lec#4 , Oct 2014 © Ahmad El-Banna
32 ECE-312 , Lec#4 , Oct 2014 © Ahmad El-Banna
• For more details, refer to: • Chapter 5 at
R. Boylestad, Electronic Devices and Circuit Theory, 11th edition, Prentice Hall. • The lecture is available online at: • http://bu.edu.eg/staff/ahmad.elbanna-courses/11966 • For inquires, send to: •
[email protected]
33 ECE-312 , Lec#1 , Oct 2014 © Ahmad El-Banna