1.

If H(s)=\(\frac{1}{s^2+s+1}\) represent the transfer function of a low pass filter (not Butterworth) with a pass band of 1 rad/sec, then what is the system function of a high pass filter with a cutoff frequency of 1rad/sec?(a) \(\frac{100}{s^2+10s+100}\)(b) \(\frac{s^2}{s^2+s+1}\)(c) \(\frac{s^2}{s^2+10s+100}\)(d) None of the mentionedI have been asked this question in an interview for internship.The doubt is from Design of Low Pass Butterworth Filters in section Digital Filters Design of Digital Signal Processing

Answer»

Right choice is (B) \(\FRAC{s^2}{s^2+s+1}\)

Easiest explanation: The low PASS-to-high pass TRANSFORMATION is

s→Ωu/s

Hence the REQUIRED high pass filter is

Ha(s)= H(s)|s→1/s

=\(\frac{s^2}{s^2+s+1}\)



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