49596

49596 - EE 541 Class Lecture Week 6 Transconductor...

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EE 541 Class Lecture Week 6 Prof. John Choma, Professor Department of Electrical Engineering- Electrophysics University of Southern California University Park; MC: 0271; PHE #604 Los Angeles, California 90089-0271 213-740-4692 [USC Office] 213-740-7581 [USC Fax] johnc@usc.edu Transconductor Applications Fall 2006 Semester
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University of Southern California Choma: EE 541 128 Overview Of Lecture Overview Of Lecture z Miscellaneous Applications ± Open Loop Integrator ± Active Tunable Resistance ± Lowpass Tunable Amplifiers ± Gyrator-Based Active Inductors ± Impedance Transformers ± Quadrature Oscillator z Biquadratic Filters ± Filter Examples ² Lowpass ² Highpass ² Bandpass ² Notch ² Delay ± Generalized Architecture
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University of Southern California Choma: EE 541 129 + V s R s C V o + G m Phase Inverting + V s R s C V o + G m Non-Phase Inverting + + V s R s C V o z Conventional Op-Amp Integrator ± Feedback Demands Op-Amp Pole Dominance ± Band-Limited By Op-Amp Compensation ± Unity Gain Frequency ( ω m ) Dependent On Source Resistance z Transconductor Integrator (OTA-C) ± Open Loop; No Feedback ± Better Frequency Response Than Op-Amp ± Unity Gain Frequency Independent Of Source Resistance z Note 90º Phase Shift In All Integrators om s s V ω 1 Vs R Cs =− omm s VG ω ±± == Active Integrators Active Integrators
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University of Southern California Choma: EE 541 130 + V s R s C V o V o + G m Phase Inverting GV mi r o C o C r C C i + V s R s + V i z Ideal Integrator ± Infinite Input Impedance ± Infinite Output Impedance ± 90º Relative Phase Shift z Practical Integrator ± Input Capacitance (C i ) ± Output Capacitance (C o ) ± Feedback Capacitance (C r ) ± Output Resistance (r o ) omu s VG ω Vs Cs =− mo r o s 12 s Gr 1 z V V ss 11 p p    ++ z Design Objectives ± Negligible C r (Plausible For Multistage) ± Small Source Resistance, R s ± Very Large r o ± Dominant Net Output Capacitance OTA OTA - - C (Integrator) Model C (Integrator) Model
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University of Southern California Choma: EE 541 131 OTA OTA - - C Transfer Relationship C Transfer Relationship z Pole Dominance ± Set At Output Port ± Large r o ± Appended Capacitance, C z Error Function V o GV mi r o C o C r C C i + V s R s + V i ( ) oo 12 1 11 1 rC C pp p +≈≈ + m r r G z C = () s i s i 12 2 11 Rr C CC RC pp p =+ mo r o s s Gr 1 z V H(s) V ss p p    == ++ u r u 1 2 ω s 1 sz ω ε (s) s p s sp =− r 1 2 s 1 z ε (s) p s ± m u o G ω = +
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University of Southern California Choma: EE 541 132 u r u 1 2 ω s 1 sz ω H(s) ε (s) s p s 11 sp    =− ++ z Error Function ± Ideally Is Unity For All Frequencies ± Unity Approximation Requires: z Design For Acceptable Integration Characteristics ± Error Magnitude Must Approach Unity Over Desired Passband ± Error Phase Must Approach Zero Over Desired Passband ² Equivalently, Integrator Delay, Which Is Negative Frequency Derivative Of Phase, Must Approach Zero Over Passband ² Phase Or Delay Characteristics More Difficult To Satisfy Than Magnitude r 1 2 s 1 z ε (s) p s
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49596 - EE 541 Class Lecture Week 6 Transconductor...

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