Attached to this post is a LTspice simulation of a highpass (Fc = 400 Hz) and a lowpass (Fc = 800 Hz) 3rdorder active filters with op amps. My question is whether or not it is possible to calculate Q of the filters based on the values of resistance and capacitance of the filters.
Based on what is advised in the book Op Amps for Everyone by Mancini, as I am interested in getting as low of a Q as possible, I simulated a Bessel 3rd order unity gain highpass filter and found that with respect to frequency one octave below the cutoff frequency, attenuation is only 12 dB when it should be 18 dB given that it is supposed to be 3rd order. I would prefer the design from Mancini as I know in advance that it has the lowest possible Q, but it also needs to truly be a 3rd order filter.
If anyone knows the answer to this I will be appreciative.
Thanks in advance,
Pete
Based on what is advised in the book Op Amps for Everyone by Mancini, as I am interested in getting as low of a Q as possible, I simulated a Bessel 3rd order unity gain highpass filter and found that with respect to frequency one octave below the cutoff frequency, attenuation is only 12 dB when it should be 18 dB given that it is supposed to be 3rd order. I would prefer the design from Mancini as I know in advance that it has the lowest possible Q, but it also needs to truly be a 3rd order filter.
If anyone knows the answer to this I will be appreciative.
Thanks in advance,
Pete
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