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I know that we can make a band pass filter by arranging a passive Low pass filter & passive high pass filter in series, and I have found lot of information on the Internet in this regard.

But what about making a band stop filter from combination of low pass filter and high pass filter? How that can be done? I am unable to find sufficient satisfactory information in this regard.

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    \$\begingroup\$ Describe the details. What is the lower frequency for the stop band? What is the upper frequency? What is the source impedance? What is the impedance being driven? Write more! \$\endgroup\$
    – jonk
    Dec 11, 2021 at 7:32
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    \$\begingroup\$ "I am unable to find sufficient satisfactory information" Well, this link popped out second in the google search. It provides a lot of information. And so does the third link and the next one... What information are you looking for if that is not sufficient? \$\endgroup\$
    – Maple
    Dec 11, 2021 at 7:50

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You simply connect them in parallel, instead of series. One passes low band trough, another passes high band through. Then the outputs are combined, and whatever did not come through one of the filters will be lost.

band stop filter

Image from electronics-tutorials

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  • \$\begingroup\$ ...unless you just design the filter as a bandstop, from the start. \$\endgroup\$ Dec 11, 2021 at 10:01
  • \$\begingroup\$ @aconcernedcitizen The OP specifically asked about "making band stop filter from combination of low pass filter and high pass filter" \$\endgroup\$
    – Maple
    Dec 11, 2021 at 10:05
  • \$\begingroup\$ Exactly how do you connect the passive low and high pass filters 'in parallel' to form a band stop filter? \$\endgroup\$ Dec 11, 2021 at 10:35
  • \$\begingroup\$ @Maple Yes, my comment was intended a a hint to OP. \$\endgroup\$ Dec 11, 2021 at 11:06
  • \$\begingroup\$ @BruceAbbott You can get some resemblence of a bandstop (with a difference), but it does require the corner frequencies to be well separated (2 decades or more). That's why I mentioned the direct design (aka the usual way). I suspect it's a teacher's question, not much value practically. \$\endgroup\$ Dec 11, 2021 at 11:10

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