Question
What are the characteristics of an elliptical filter?
Answer Options
- A) Gradual passband rolloff with minimal stop-band ripple
- B) Extremely flat response over its pass band with gradually rounded stop-band corners
- C) Extremely sharp cutoff with one or more notches in the stop band
- D) Gradual passband rolloff with extreme stop-band ripple
Correct Answer: C
Explanation
The elliptical filter (also known as a Cauer filter) is considered the most powerful class of filter because it achieves the steepest possible rate of cutoff (the fastest rolloff from passband to stopband) for a given order (number of components). It surpasses even the Chebyshev design in selectivity.
The elliptical filter achieves this extreme selectivity by sacrificing flatness in both regions. Its distinct characteristics are an extremely sharp cutoff rate combined with the unique feature of having one or more notches (points of infinite attenuation) in the stop band. This makes it an ideal filter when very high out-of-band rejection is required immediately next to the desired signal.
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