filter - 1 Advanced Analog IC Design Professor Y. Chiu EECT...

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Unformatted text preview: 1 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 Active Filters Introduction 2 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 Filtering : most common linear time-invariant (LTI) signal processing function selecting the signal bandwidth of interest (in reality neither linear nor time-invariant) Categories : continuous time (CT), discrete time (DT) analog filter, digital filter (will focus on CT analog filters for this course) Frequency domain : lowpass (LP), highpass (HP), bandpass (BP) Time domain : impulse response, FIR, IIR Simple R-C Filter 3 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 R C V i V o Continuous-time, 1st-order, one real pole, lowpass j s-plane s p =- ( 29 sRC sC R sC s V V s H i o + = + = = 1 1 1 1 ) ( RC s p 1- =- = Simple R-C Filter 4 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 H(t) t 1/ e-t/ |H(j)| 1 -20dB/dec-6dB/oct H(j)-45 -90 Frequency response Impulse response RC RC t for e t h t 1 , , 1 ) ( = = =- General Filter Specs 5 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 More realistic: Magnitude response p, s, p, and s Phase response Ideal LPF: Non-causal Infinite complexity |H(j)| 1 |H(j)| 0dB p p- passband ripple (< 1dB) s- stopband attenuation s Transition band Passband Stopband Example: 2nd-order VTF 6 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 Continuous-time Where are the poles? (complex conjugate poles for maximum flatness) Lowpass, highpass, or bandpass? ( 29 b as s b s V V s H i o + + = = 2 ) ( Passive R-L-C Filter 7 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 R C V i V o L No active component (low power) Inductors are bulky and expensive to realize in ICs Values of R, L, and C will not track each other LC L R s s LC s H 1 1 ) ( 2 + + = Active OP-R-C Filter 8 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 Its active Inductor-less Area efficient Values of Rs and Cs and their time co.s wont track each other may lead to RC time constant variations of as high as 20% RC time constant enters the VTF in product form can be tuned for accuracy R 1 C A R R R 3 R 4 C B R 2 V i V o Assuming ideal op amps, B A B B A C C R R C R s s C C R R s H 3 2 4 2 3 1 1 1 1 ) ( + +- = Continuous-Time Integrator 9 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 C 2 V i V o R 1 Assuming ideal op amp, ( 29 ( 29 1 2 1 t o in v t v d R C - = - ( 29 ( 29 1 2 1 1 o i V H s s V s R C = = - 10 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 Cascade Filter Design Biquads Cascade Filter Design 11 Advanced Analog IC Design Professor Y. Chiu EECT 7329 Fall 2011 j s-plane For a real-coefficient H(s):...
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filter - 1 Advanced Analog IC Design Professor Y. Chiu EECT...

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