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Which of the following is a low pass-to-band stop transformation?(a) s→\(\frac{s(Ω_u-Ω_l)}{s^2+Ω_u Ω_l}\)(b) s→\(\frac{s(Ω_u+Ω_l)}{s^2+Ω_u Ω_l}\)(c) s→\(\frac{s(Ω_u-Ω_l)}{s^2-Ω_u Ω_l}\)(d) none of the mentionedThis question was posed to me by my college professor while I was bunking the class.This intriguing question comes from Frequency Transformations topic in chapter Digital Filters Design of Digital Signal Processing

Answer»

Correct choice is (c) s→\(\frac{s(Ω_u-Ω_l)}{s^2-Ω_u Ω_l}\)

Best EXPLANATION: If Ωu and Ωl are the upper and lower cutoffpass band frequencies of the desired band STOP FILTER, then the TRANSFORMATION to be performed on the NORMALIZED low pass filter is

s→\(\frac{s(Ω_u-Ω_l)}{s^2-Ω_u Ω_l}\)



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