What is the order of the filter, when the gain decreases at the rate of 60dB/decade?

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ISRO VSSC Technical Assistant Electronics 2018 Official Paper
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  1. Second-order low pass filter
  2. Third order high pass filter
  3. Third order low pass filter
  4. None of the above

Answer (Detailed Solution Below)

Option 3 : Third order low pass filter
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Detailed Solution

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Explanation:

Low pass filter

The low pass filter only allows low-frequency signals from 0Hz to its cut-off frequency, ƒc point to pass while blocking those any higher.

This is designed with passive components in two different structures.

RC Low pass filter

F1 Pinnu 22.9.20 Pallavi D2

RL Low pass filter

F1 Pinnu 22.9.20 Pallavi D3

The ideal frequency response of the LPF is:

F1 Pinnu 22.9.20 Pallavi D4

The frequency-domain analysis of the low pass filter is shown below and this is for the first order.

F1 Pinnu 22.9.20 Pallavi D5

If the system functions contain the one pole then the change in slope will be 20 dB/decade, but in the given question the gain decreases at the rate of 60dB/decade so it means it contains the order three and poles also will be three.

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