Hi,

I need to make a few passive filters for my school project. Everything was fine, until I got to the band pass and band block filters. I seem to get some weird results when the signal passes through them. When it blocks them it's fine, but just when it passes I get massive distortions. The bode plotter characteristics look fine. Anyway, I have included the screenshots from multisim? Any ideas on how to fix this? Tnx.

 

hi sv,
Welcome to AAC,
This what I see with LTSpice.
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EDIT:
Changed Vin from Sine to Square.

 

I can't get that. I have also made the circuits on PCB, same thing. Maybe I should try different values for resistors and capacitors? Btw I need to use square signals on that.

 

hi,
Could you give a description of what you want to achieve with the circuit.?
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Note: my first 2 plots used a Sine wave source.

 

I need to black a band of frequencies (that's what the band stop is for) and block everything else but the band (band pass). I need to do this using only passive components. The range of the band is not defined.

 

OK,
What are the details of the input signal.?
Is it a sine or square wave?
What is its amplitude.?
What will be centre frequency of the filter.?
How 'sharp/steep' do you want the band stop/pass about the centre frequency.?

I guess you know that the output signal amplitude will lower than the input amplitude, is that going to be a problem.

 

So I took a 10 cascade high-pass filter and a 10 cascade low-pass filter. When the input signal 1B output turned 33mV. The best filter can be built using inductance.

 

Have a look at these calculators, and see how they work.
RLC Band-Pass Filter Design Tool

sim.okawa-denshi.jp › Tools › Filters This page is a web application that design a RLC band-pass filter. Use this utility ... Calculate the transfer function for RLC band-pass filter with R, L and C values ...

And on this site under tools.......
Bandpass Filter Calculator - Electrical Engineering & Electronics Tools

https://www.allaboutcircuits.com › Tools Calculating Inductance and Capacitance of a Bandpass Filter. This calculator helps determine the correct values of the inductance (L) and capacitance (C) of an .

There is a wealth of information on this site and on the internet if you google the appropriate type of filter you require.

 

Hi Eric,
The input signal will be a square wave, low amplitude (no more than 5V). The frequencies and 'sharpness' and 'steepness' don't really matter, this will just be a project to show student what does a filter do, so the exact numbers don't matter, just the oscilograph.

Hi Bordodynov,
So you suggest I should try and combine inductors and capacitors in the same filter? Thanks, will try that too!

Hi recklessrog,
Thanks for the links, but I already know about those, google is where I got the schematics for my current build. My goal is to user only RC and CR pairs and build the band pass and band stop filters.

 

hi sv,
One option is to show the student the response of the high and low pass filters on the same plot.
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