ELEC212 Chapter 7 Filter Design Techniques Part 1

ELEC212 Chapter 7 Filter Design Techniques Part 1 -...

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1 The Hong Kong University of Science and Technology Department of Electronic and Computer Engineering ELEC 212 Chapter 7 IIR Filter Design Techniques 2 09-10 Fall ELEC 212 IIR Filter Design Techniques Introduction ± The design of filters involves the following stages: –T h e specification of the desired properties of the system h e approximation of the specifications using a causal discrete-time system h e realization of the system ( recall previous lecture ) ± These steps are certainly not independent ± We focus primarily on the second step – First step largely depends on specific application – Third step largely depends on specific technology used for implementation ± Specifications for both the discrete-time filter and the effective continuous- time filter are typically given in the frequency domain – This is especially common for frequency-selective filters such as lowpass, bandpass and highpass filters 3 09-10 Fall ELEC 212 IIR Filter Design Techniques Design Specification ± Specifications are given in frequency-domain in terms of the desired magnitude and phase responses of the filter ± The phase specification of the filter is constrained by the stable and causal properties ± Specifications: – Sampling rate of the system – Passband frequency – Stopband frequency – Transition band (width) – Passband ripple – Stopband ripple – Stopband attenuation (gain) ± Usually measured in dB Objective: design a system function of a discrete-time system which has frequency- response falling within tolerances and meeting cut-off frequency specifications. 4 09-10 Fall ELEC 212 IIR Filter Design Techniques Discrete-Time IIR Filter Design ± Common method for IIR filter design: Transform a continuous-time filter into a discrete-time filter meeting prescribed specifications I.e., map s -plane to z -plane to obtain desired IIR filter ± Alternative method : Directly design IIR digital filter in z -plane I.e., select poles and zeros in z -plane directly, and adjust their locations according to prescribed specifications iteratively to approach the response ± We will focus on designing discrete-time IIR filters based on continuous- time filters . Why: 1. Continuous-time IIR filter design is highly advanced . It is advantageous to use the design procedures already developed for continuous-time filters 2. Many useful continuous-time IIR design methods have relatively simple closed-form design formulas . Therefore, discrete-time IIR filter design methods based on such standard continuous-time filter design formulas are rather simple to carry out 3. Standard approximation methods that work well for continuous-time IIR filters do not lead to simple closed-form design formulas when these methods are applied directly to the discrete-time IIR case
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5 09-10 Fall ELEC 212 IIR Filter Design Techniques Conversion from Continuous-Time Filters to Discrete-Time IIR Filters ± To convert from continuous-time prototype filter to discrete-time IIR filter, we must obtain H(z) from H a (s) ±
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This note was uploaded on 03/27/2011 for the course ELEC 212 taught by Professor Prof.matthewmckay during the Spring '11 term at HKUST.

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ELEC212 Chapter 7 Filter Design Techniques Part 1 -...

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