Chương 7: Frequency Response

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Frequency of applied signal has effect on response of circuit Plots of effect of frequency on gain and phase.

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Nội dung Text: Chương 7: Frequency Response

Frequency response Frequency Introduction  Lowfrequency analysis  Highfrequency analysis  Lowfrequency response of BJT & FET  amplifier Miller effect capacitance  Highfrequency response of BJT & FET  amplifier
Introduction Introduction Frequency of applied signal has effect on response of circuit Plots of effect of frequency on gain and phase
Frequency response analysis model analysis Capacitor is shortcircuit equivalent at high frequency open circuit equivalent at low frequency
Low-frequency analysis Low-frequency Low frequency, C is opencircuit equivalent ⇒ V =0, A =0 o v High frequency, C is shortcircuit equivalent ⇒ V =V A =1 o i, v
High-frequency analysis High-frequency Low frequency, C is opencircuit equivalent ⇒ V =V ,A =1 o i v High frequency, C is shortcircuit equivalent ⇒ V =0 , A =0 o v
Bode plot Cutoff frequency: gain is Cutoff frequency: gain is reduced by a factor of 0.707 f1 cutoff frequency at low frequency f2 cutoff frequency at high frequency
Low-frequency response of BJT amplifier BJT Low frequency limitation is fLs, fLo, fLe, which is  determined by Cin, Cout, Cemitter, respectively Low frequency is the highest of fLs, fLo, fLe 
Cutoff low-frequency by source capacitance by fLs=1/[2π(Rs+Ri)Cs] with Ri=R1//R2//βre
Cutoff low-frequency by output capacitance by fLo=1/[2π(Ro+RL)Cc] with Ro=RC//ro
Cutoff low-frequency by emitter capacitance by fLE=1/[2πReCE] with Re=RE//(Rs’/β+re)
Low frequency response of FET Low Similar to BJT  VDD 3 capacitors concerned: CG, 5V  VDD CC, CS RD fLG=1/[2π(Rsig+Ri)CG] in the Cc  1 plot Ri=RG Q1 CG Rsig 5 7 fLC=1/[2π(Ro+RL)CC] in the 6  plot Ro=RD//rd 4 Vs 3 fLs=1/[2π(ReqCs] in which RL RG RS  Cs Req=Rs/[1+Rs(1+gmrd)/ 0 (rd+RD//RL)]
Miller effect capacitance Miller Cf: feedback capacitance   Amplifier with negative voltage gain Input, output capacitance is increased by a Miller effect capacitance CMi=(1Av)Cf CMo=(11/Av)Cf≈Cf
High-frequency response of BJT amplifier BJT High frequency limitation is determined by parasitic capacitors Cbc, Cce, Cbe, Cwi, Cwo
High-frequency response of BJT amplifier BJT Ci=CWi+Cbe+Cmi Co=CWo+Cce+CMi
High-frequency response of BJT amplifier BJT
High frequency response of FET High VDD 5V VDD RD Cgd Cc 1 6 Q1 CG Rsig Cds 5 7 Cgs 4 Vs 3 RG RS RL CWi Cs CWo 0 Read 11.10 page 546, Electronic devices and circuit theory
Homework Homework Chapter 11: 10, 11, 15, 17, 18, 19, 22, 26,  28, 29, 32