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Butterworth Pi LC Low Pass Filter Calculator
The characteristic of the Butterworth filter is that the frequency response curve in the pass band is flat to the maximum without fluctuations, while it gradually drops to zero in the stop band. On the Bode plot of the logarithm of amplitude versus angular frequency, starting from a certain boundary angular frequency, the amplitude gradually decreases as the angular frequency increases, tending to negative infinity.
The attenuation rate of a first-order Butterworth filter is 6 dB per octave and 20 dB per decade. The attenuation rate of a second-order Butterworth filter is 12 dB per octave, the attenuation rate of a third-order Butterworth filter is 18 dB per octave, and so on. Butterworth filter amplitude diagonal frequency
It decreases monotonically and is the only filter whose amplitude versus diagonal frequency curve maintains the same shape regardless of order. It's just that the higher the filter order, the faster the amplitude attenuates in the stop band. For other filters, the amplitude versus corner frequency plot for higher orders has a different shape than the amplitude versus corner frequency for lower orders.