elektronica ii ch.5 bjt ac analysis. 5.1 introduction ch.3 transistor: basic construction,...
TRANSCRIPT
![Page 1: Elektronica II Ch.5 BJT AC Analysis. 5.1 Introduction Ch.3 Transistor: basic construction, appearance, characteristics Ch.4 Transistor: biasing Ch.5 AC](https://reader033.vdocuments.net/reader033/viewer/2022061305/55142204550346ec488b5897/html5/thumbnails/1.jpg)
Elektronica II
Ch.5 BJT AC Analysis
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5.1 Introduction
Ch.3 Transistor: basic construction, appearance, characteristics
Ch.4 Transistor: biasing Ch.5 AC response BJT amplifier by
reviewing the (small-signal) models re, hybrid π and hybrid equivalent
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5.2 Amplification in the AC domain
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5.3 BJT transistor modeling
hybrid equivalent model: specification sheets include parameters, defined for a specific set of operating conditions (Ic, Vce, f)
re model: important parameter determined by actual operating conditions
hybrid π model: high-frequency analysis
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5.3 BJT transistor modeling (cont’d)
AC equivalent model is obtained by:1. Setting all dc sources to zero and replacing them
by a short-circuit equivalent2. Replacing all capacitors by short-circuit equivalent3. Removing all elements bypassed by the short-
circuit equivalents introduced by steps 1 and 24. Redrawing the network in a more convenient and
logical form
Parameters: Vi, Ii, Zi, Vo, Io, Zo, Av, Ai
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5.3 BJT transistor modeling (cont’d)
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5.4 The re transistor model
Common-Base Configuration Common-Emitter Configuration Common-Collector Configuration (use
model defined by CE configuration)
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5.4 The re transistor model (cont’d)Common-Base Configuration
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5.4 The re transistor model (cont’d)Common-Base Configuration
Typical values of Zi range from a few ohms to a maximum of about 50 Ω
Typical values of Zo are in the mega-ohm range In general, the input impedance is relatively small and
the output impedance quite high
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5.4 The re transistor model (cont’d)CB-Amplifier
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5.4 The re transistor model (cont’d)CB-Amplifier (example 5.11)
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5.4 The re transistor model (cont’d)Common-Emitter Configuration
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5.4 The re transistor model (cont’d)Common-Emitter Configuration
Typical values of Zi defined by βre range from a few hundred ohms to the kilo-ohm range, with a maximum of about 6 kΩ to 7 kΩ
Typical values of Zo are in the range of 40 kΩ to 50 kΩ
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5.4 The re transistor model (cont’d)CE-Amplifier: Fixed-bias
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5.4 The re transistor model (cont’d)CE-Amplifier: Fixed-bias
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5.4 The re transistor model (cont’d)CE-Amplifier: Fixed-bias
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5.4 The re transistor model (cont’d) CE-Amplifier:Fixed-bias (example 5.4)
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5.4 The re transistor model (cont’d)CE-Amplifier: Voltage-divider
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5.4 The re transistor model (cont’d)CE-Amplifier: Voltage-divider
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5.4 The re transistor model (cont’d) CE-Amplifier:Voltage-divider (Example 5.5)
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5.4 The re transistor model (cont’d) CE-Amplifier:Voltage-divider (Example 5.8)
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5.4 The re transistor model (cont’d) CE-Amplifier:Voltage-divider (Example 5.9)
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5.4 The re transistor model (cont’d) Other configurations
=> 5.8 common-emitter fixed-bias: Zi, Zo, Av, phase relationship, example 5.4=> 5.9 voltage-divider bias:
=> Re bypassed, with ro : Zi, Zo, Av, phase relationship, example 5.5 en 5.9=> Re unbypassed, with ro : example 5.8
=> 5.10 ce emmitter-bias:=> Re unbypassed, without ro : Zi, Zo, Av, phase relationship=> Re unbypassed, with ro: Zi, Zo, Av=> bypassed => zie ce fixed-bias-> example 5.6 (unbypassed, with ro) en 5.7 (bypassed, with ro)
=> 5.11 emitter-follower:=> without ro : Zi, Zo, Av, phase relationship=> with ro : Zi, Zo, Av-> example 5.10: without en with ro=> variaties: with voltage-divider biasing en with collector resistor Rc
=> 5.12 common-base configuration: Zi, Zo, Av, Ai: example 5.11=> 5.13 collector feedback:
=> without Re:=> without ro: Zi, Zo, Av, phase relationship=> with ro: Zi, Zo, Av-> example 5.12: without en with ro
=> with Re: exercise=> 5.14 collector dc feedback: with ro: Zi, Zo, Av, phase relationship, example 5.13
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5.15 Determining the current gain
For each transistor configuration, the current gain can be determined directly from the voltage gain, the defined load and the input impedance
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5.15 Determining the current gain (cont’d)
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5.16 Effect of RL and RS
Two approaches can be used: By inserting the (re model) equivalent
circuit and use methods of analysis to determine the quantities of interest
By defining a two-port equivalent model and use the parameters determined for the no-load situation
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5.16 Effect of RL and RS (cont’d) 1st approach
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5.16 Effect of RL and RS (cont’d)
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5.16 Effect of RL and RS (cont’d)
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5.16 Effect of RL and RS (cont’d) Fixed-bias
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5.16 Effect of RL and RS (cont’d) Fixed-bias
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5.16 Effect of RL and RS (cont’d) Fixed-bias: example 5.14
- Voltage divider
- Emitter follower
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5.17 2nd (Two-port systems) approach (effect of RL and RS)
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5.17 Two-port systems approach (effect of RL and RS) (cont’d)
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5.17 Two-port systems approach (effect of RL and RS) (cont’d)
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5.17 Two-port systems approach (effect of RL and RS) (cont’d)
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5.17 Two-port systems approach (effect of RL and RS) (cont’d) Example 5.15
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5.18 Summary tables
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5.18 Summary tables (cont’d)
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5.19 Cascaded systems