BJT Frequency Response -...
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07/10/58
1
BJT Frequency Response
LF Response, Miller Theorem & HF Response
M2-3 Electrinics 1/30
FR; Outline
- Introduction
- Decibels
- Bode Plot (Frequency Response)
- Low Frequency Analysis
- Miller Theorem
Hi h F A l i- High Frequency Analysis
M2-3 Electrinics 2/30
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Introduction
- Previously, effects of capacitive elements y, pare ignored
- Capacitor affect the LF & HF of amplifiers
- Swept Frequencies are used to test- Logarithmic scales are both used in gain & frequency axes
M2-3 Electrinics 3/30
Logarithm (I)
- Logarithm
M2-3 Electrinics 4/30
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Logarithm (II)
- Some useful logarithm
M2-3 Electrinics 5/30
Logarithm (III)
- Semilog scale
M2-3 Electrinics 6/30
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Important points in log scale
M2-3 Electrinics 7/30
Decibels- Bel is the surname of Alexander Graham Bell
M2-3 Electrinics 8/30
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Advantage of Logarithm
Gain calculation made easier
M2-3 Electrinics 9/30
Example of gain calculation
M2-3 Electrinics 10/30
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General Frequency Considerations
RC coupling
M2-3 Electrinics 11/30
Cut-Off or Half-Power Frequency
M2-3 Electrinics 12/30
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Bandwidth, BW
Linear
Log
M2-3 Electrinics 13/30
Phase plot
M2-3 Electrinics 14/30
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Low Frequency Analysis
@ Hi h F@ High Frequency
@ DCM2-3 Electrinics 15/30
Voltage Divider
M2-3 Electrinics 16/30
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Gain Equation
M2-3 Electrinics 17/30
Bode Plot of Low Frequency Region
M2-3 Electrinics 18/30
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Example of LF Bode Plot
M2-3 Electrinics 19/30
Phase response of LF region
M2-3 Electrinics 20/30
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Miller Effect Capacitance (I)
M2-3 Electrinics 21/30
Miller Effect Capacitance (II)
CMo ~ Cf ; AV >>1M2-3 Electrinics 22/30
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High Frequency Analysis
M2-3 Electrinics 23/30
Parasitic Capacitances
M2-3 Electrinics 24/30
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HF Model of BJT Amplifier
M2-3 Electrinics 25/30
Parameter Variation
M2-3 Electrinics 26/30
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Full Frequency Response
M2-3 Electrinics 27/30
Square-wave Testing
M2-3 Electrinics 28/30
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Results of Square-wave Tesing
M2-3 Electrinics 29/32
Rise Time & Tilt
orWh f i hi h t ff & f or
M2-3 Electrinics 30/32
Where fHi is high cut off & fLo
is low cut off frequencies.The fs is the frequency of square wave signal
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Rise Time & Tilt; example
M2-3 Electrinics 31/32
Memo
M2-3 Electrinics 32/32