BJT Frequency Response - KMUTTwebstaff.kmutt.ac.th/~werapon.chi/M2_3/1_2014/M2_3_Lecture_07_… ·...
Transcript of BJT Frequency Response - KMUTTwebstaff.kmutt.ac.th/~werapon.chi/M2_3/1_2014/M2_3_Lecture_07_… ·...
BJT Frequency Response
LF Response, Miller Theorem & HF Response
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FR; Outline
- Introduction - Decibels - Bode Plot (Frequency Response) - Low Frequency Analysis - Miller Theorem - High Frequency Analysis
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Introduction
- Previously, effects of capacitive elements are ignored
- Capacitor affect the LF & HF of amplifiers - Swept Frequencies are used to test - Logarithmic scales are both used in gain & frequency axes
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Logarithm (I)
- Logarithm
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Logarithm (II)
- Some useful logarithm
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Logarithm (III)
- Semilog scale
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Important points in log scale
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Decibels
- Bel is the surname of Alexander Graham Bell
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Advantage of Logarithm
Gain calculation made easier
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Example of gain calculation
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General Frequency Considerations
RC coupling
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Cut-Off or Half-Power Frequency
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Bandwidth, BW
Linear
Log
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Phase plot
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Low Frequency Analysis
@ High Frequency
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Voltage Divider
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Gain Equation
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Bode Plot of Low Frequency Region
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Example of LF Bode Plot
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Phase response of LF region
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Miller Effect Capacitance (I)
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Miller Effect Capacitance (II)
CMo ~ Cf ; AV >>1
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High Frequency Analysis
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Parasitic Capacitances
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HF Model of BJT Amplifier
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Parameter Variation
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Full Frequency Response
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Square-wave Testing
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Results of Square-wave Tesing
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Rise Time & Tilt
or
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Where fHi is high cut off & fLo is low cut off frequencies. The fs is the frequency of square wave signal
Rise Time & Tilt; example
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Memo
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Free Logarithmic Graph Paper from http://incompetech.com/graphpaper/logarithmic/
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Free Logarithmic Graph Paper from http://incompetech.com/graphpaper/logarithmic/
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