I have a low pass filter with 3db cut off frequency of 200Hz and a high pass passive filter with 3db cut off frequency of 2kHz.
I need to design a cascaded band pass filter which will isolate signals for each range.
The low-frequency components (20 to 150 Hz) will control Blue LED lights, the mid-frequency components (200 Hz to 2 kHz) will control Green LED lights, and the high-frequency components (2.5 kHz to 20 kHz) will control Red LED lights.
My transfer function for cascaded band pass filter is as below
$$
H(j\omega)= \frac{sR_2C_2}
{1+sR_2C_2+sR_1C_1+s^2R_1R_2C_1C_2}
$$
where \$s=j\omega\$ . In order to isolate the signals, my design will have to be low pass-band pass-high pass filter. Is it correct? I would like to know how to determine lower and upper cut off frequency. Is it 200Hz and 2kHz?
Best Answer
And...
If you cascaded those filters you won't get what you want - the low pass would start to remove frequencies above 200 Hz and the high pass would start to remove frequencies below 2 kHz. In between those two frequencies you would get very little signal i.e. this is a band-reject filter.
If you had a low-pass filter that had a cut-off of 2 kHz cascaded with a high-pass filter that has a cuto-off of 200 Hz, that would work: -