Chương 7: Frequency Response docx

Frequency response Frequency response  Introduction Introduction  Low-frequency analysis Low-frequency analysis  High-frequency analysis High-frequency analysis  Low-frequency response of BJT & Low-frequency response of BJT & FET amplifier FET amplifier  Miller effect capacitance Miller effect capacitance  High-frequency response of BJT & High-frequency response of BJT & FET amplifier FET amplifier Introduction Introduction Frequency of applied Frequency of applied signal has effect on signal has effect on response of circuit response of circuit Plots of effect of Plots of effect of frequency on gain frequency on gain and phase and phase Frequency response Frequency response analysis model analysis model Capacitor is Capacitor is short-circuit short-circuit equivalent at equivalent at high frequency high frequency open-circuit open-circuit equivalent at equivalent at low frequency low frequency Low-frequency analysis Low-frequency analysis Low frequency, Low frequency, C is C is open-circuit open-circuit equivalent equivalent ⇒ V V o o =0, A =0, A v v =0 =0 High frequency, High frequency, C is C is short-circuit short-circuit equivalent equivalent ⇒ V V o o =V =V i, i, A A v v =1 =1 High-frequency analysis High-frequency analysis Low frequency, Low frequency, C is C is open-circuit open-circuit equivalent equivalent ⇒ V V o o =V =V i i ,A ,A v v =1 =1 High frequency, High frequency, C is C is short-circuit short-circuit equivalent equivalent ⇒ V V o o =0 , A =0 , A v v =0 =0 Bode plot Bode plot Cutoff frequency: gain Cutoff frequency: gain is reduced by a is reduced by a factor of 0.707 factor of 0.707 f f 1 1 cutoff frequency at cutoff frequency at low frequency low frequency f f 2 2 cutoff frequency at cutoff frequency at high frequency high frequency Low-frequency response of Low-frequency response of BJT amplifier BJT amplifier  Low frequency limitation is f Low frequency limitation is f Ls Ls , f , f Lo Lo , f , f Le Le , which is , which is determined by C determined by C in in , C , C out out , C , C emitter emitter , respectively , respectively  Low frequency is the highest of f Low frequency is the highest of f Ls Ls , f , f Lo Lo , f , f Le Le Cutoff low-frequency Cutoff low-frequency by source capacitance by source capacitance f f Ls Ls =1/[2 =1/[2 π π (R (R s s +R +R i i )C )C s s ] with R ] with R i i =R =R 1 1 //R //R 2 2 // // β β r r e e Cutoff low-frequency Cutoff low-frequency by output capacitance by output capacitance f f Lo Lo =1/[2 =1/[2 π π (R (R o o +R +R L L )C )C c c ] with R ] with R o o =R =R C C //r //r o o Cutoff low-frequency Cutoff low-frequency by emitter capacitance by emitter capacitance f f LE LE =1/[2 =1/[2 π π R R e e C C E E ] with R ] with R e e =R =R E E //(R //(R s s ’/ ’/ β β +r +r e e ) ) [...]... increased by a Miller effect capacitance CMi=(1-Av)Cf CMo=(1-1/Av)Cf≈Cf  High -frequency response of BJT amplifier High frequency limitation is determined by parasitic capacitors Cbc, Cce, Cbe, Cwi, Cwo High -frequency response of BJT amplifier Ci=CWi+Cbe+Cmi Co=CWo+Cce+CMi High -frequency response of BJT amplifier High frequency response of FET VDD 5V VDD RD Cgd Cc 1 6 Q1 CG 5 Rsig Cds 7 Cgs 4 Vs 3 RG CWi...Low frequency response of FET  VDD 5V  VDD RD Cc  1 Q1 CG Rsig 5 7 6  4 Vs 3 RG 0 RS RL Cs  Similar to BJT 3 capacitors concerned: CG, CC, CS fLG=1/[2π(Rsig+Ri)CG] in the plot Ri=RG fLC=1/[2π(Ro+RL)CC] in . Frequency response Frequency response  Introduction Introduction  Low -frequency analysis Low -frequency analysis  High -frequency analysis High -frequency analysis  Low -frequency response. cutoff frequency at cutoff frequency at high frequency high frequency Low -frequency response of Low -frequency response of BJT amplifier BJT amplifier  Low frequency limitation is f Low frequency. amplifier Introduction Introduction Frequency of applied Frequency of applied signal has effect on signal has effect on response of circuit response of circuit Plots of effect of Plots of effect of frequency on gain frequency