Lecture29-OP Amp Frequency Response

Lecture29-OP Amp Frequency Response - Lecture 29...

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ECE 3040 - Dr. Alan Doolittle Georgia Tech Lecture 29 Operational Amplifier frequency Response Reading: Jaeger 12.1 and Notes
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ECE 3040 - Dr. Alan Doolittle Georgia Tech Ideal Op Amps Used to Control Frequency Response Low Pass Filter + - R2 R1 V in V out + - R2 R1 V in V out C2 1 2 R R V V in out = + = + = = = s C R R R s C R s C R R V V R s C R V V j s If in out in out 2 2 1 2 2 2 2 2 1 1 2 2 1 1 1 1 1 1 , ϖ Now put a capacitor in parallel with R2: Previously:
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ECE 3040 - Dr. Alan Doolittle Georgia Tech + - R2 R1 V in V out C2 •At DC (s=0), the gain remains the same as before (-R 2 /R 1 ). •At high frequency, R 2 C 2 s>>1, the gain dies off with increasing frequency, H H in out f C R R s C s C R V V ω π = = = 2 1 1 1 2 2 1 2 2 1 Ideal Op Amps Used to Control Frequency Response Low Pass Filter + = s C R R R V V in out 2 2 1 2 1 1 •At high frequencies, more “negative feedback” reduces the overall gain
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ECE 3040 - Dr. Alan Doolittle Georgia Tech dB in expressed gain the is 20 = in out DB V V V Log A •At DC (s=0), the gain remains the same as before (-R2/R1) •At high frequency, R 2 C 2 s>>1, the gain dies off with increasing frequency •Implements a “Low Pass Filter”: Lower frequencies are allowed to pass the filter without attenuation. High frequencies are strongly attenuated (do not pass). = 1 2 20 R R Log A DB V Decade dB Slope / 20 = f H Log(f) DB V A -3dB drop at f H (V out has dropped in half!) Ideal Op Amps Used to Control Frequency Response Low Pass Filter 2 2 2 1 C R f H π =
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ECE 3040 - Dr. Alan Doolittle Georgia Tech + - R2 R1 V in V out + - R2 R1 V in V out C1 1 2 R R V V in out = s C R s C R V V s C R R V V in out in out 1 1 1 2 1 1 2 1 1 + = + = Ideal Op Amps Used to Control Frequency Response High Pass Filter •At DC (s=0), the gain is zero. •At high frequency, R 1 C 1 s>>1, the gain returns to it’s full value, (-R 2 /R 1 )
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ECE 3040 - Dr. Alan Doolittle Georgia Tech s C R s C R V V in out 1 1 1 2 1 + = Ideal Op Amps Used to Control Frequency Response High Pass Filter •At DC (s=0), the gain is zero.
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Lecture29-OP Amp Frequency Response - Lecture 29...

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