Question
Why is an anti-aliasing filter required in a decimator?
Answer Options
- A) It removes high-frequency signal components that would otherwise be reproduced as lower frequency components
- B) It peaks the response of the decimator, improving bandwidth
- C) It removes low-frequency signal components to eliminate the need for DC restoration
- D) It notches out the sampling frequency to avoid sampling errors
Correct Answer: A
Explanation
When the sampling rate of a digital signal is reduced (the process of decimation), a new, lower Nyquist frequency is established for the subsequent stages. If the digital signal contains frequency components higher than this new, lower Nyquist frequency, those components will be incorrectly ‘folded over’ into the desired narrow passband, a phenomenon called aliasing.
To prevent this, a digital anti-aliasing filter (often a low-pass filter) must be applied before the samples are discarded. This filter removes high-frequency signal components that would otherwise be reproduced as lower frequency components (aliasing) in the decimated signal, ensuring the final down-sampled data stream is clean and accurate.
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