Slide điện tử tương tự chapter 5 frequency response
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DR. PHẠM NGUYỄN THANH LOAN
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CHAPTER 5: FREQUENCY RESPONSE
Hà Nội, 9/24/2014
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Introduction
Models
Low frequency response
Miller effect
High frequency response
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Frequency Response
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Relation of gain and input
frequency: Bode diagram
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Introduction
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Introduction
f1 : fc at low frequency region
f2: fc at high frequency region
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Cut-off frequency (fc): gain
decrease of 3dB (0.707)
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Filter models
…. pass filter
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…. pass filter
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Filter models
High pass filter
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Low pass filter
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High pass filter
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Equivalent capacitor
short circuit at high frequency
open circuit at low frequency
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Model
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pass filter
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Low frequency
Open-circuit equivalent Capacitor
=>
Vo=0, Av=0
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- High
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High frequency
Short - circuit equivalent Capacitor
=> Vo=Vi, Av=1
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Model
pass filter
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- Low
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Equivalent capacitor
short circuit at high frequency
open circuit at low frequency
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Model
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pass filter
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Low frequency,
Open-circuit eq. capacitor
=>
Vo= Vi , Av= 1
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- Low
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High frequency,
Short-circuit eq. capacitor
=> Vo= 0 , Av=0
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Model
frequency
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- Cut-off
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Model
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fc: gain reduces 0,707 times (3dB)
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- Cut-off
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Low frequency response
EC amplifier
Low frequency can be
determined from:
Cin (fLs) at input
Cout (fLo) at output
Cemitter (fLe)
f1 = fL = Max( fLs, fLo, fLe )
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fc introduced by input capacitor
with
f LS
1
2 ( R S R i )C S
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R 1 / / R 2 / / re
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fc introduced by output capacitor
f Lo
1
2 ( R o R L )C C
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with
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R C / / r0
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fc introduced by emitter capacitor
f LE
1
2 R eC E
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R E / / ( re R S / )
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CG
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RG
Similar to BJT amplifier
3 capacitors: mCG, CC, CS
fLG=1/[2π(Rsig+Ri)CG] with
Ri=RG
fLC=1/[2π(Ro+RL)CC] with
Ro=RD//rd
fLs=1/[2π(ReqCs] with
Req=Rs/[1+Rs(1+gmrd)/(rd+R
D//RL)]
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FET amplifier
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RL
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Cf: feedback capacitor
Inverting amplifier
Equivalent of Input and output capacitance
CMin = (1-Av)Cf
CMout = (1-1/Av)Cf ≈ Cf when Av is very big
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Miller effect
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Vùng tần số cao bị giới
hạn bởi các khâu lọc
thông thấp do các tụ kí
sinh Cbc, Cce, Cbe, Cwi,
Cwo
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High frequency response
EC amplifier
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High frequency response
EC amplifier
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Ci=CWi+Cbe+CMi
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Co=CWo+Cce+CMo
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High frequency response
EC amplifier
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How to choose cutoff frequency?
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High frequency response
FET amplifier
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VDD
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Q1
Rsig
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Cds
Cgs
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VDD
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CG
5V
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RG
RS
CWi
RL
Cs
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Tham khảo 11.10 trang 546, Electronic devices and circuit theory
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CWo
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Given Bode diagram
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Determine ao, ao(dB) bandwidth, fc?
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A)Determine voltage gain
B) Determine fLs, flC, FlE
C) Determine fHi, fH0
D) Plot Bode diagram
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Example
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