[Question]Second-order low pass filter

[GDF]

2nd order low pass bessel filter

If we want to implement a second order low pass filter, why we use
complex conjugate poles rather than two real poles? For instance, cascade
two RC filters with different time constants.

Thanks,

 

[sunking]

second order low pass filter

for the different respond chara.
and you can simulate with different conditions

 

[flatulent]

The complex poles will produce a flatter pass band followed by a sharper increase in attenuation in the stopband. At much higher frequency both types will have the same asymptotic roll off of 12 dB/octave.

Read up on topics such as Butterworth, Chebychev, and Bessel filter polynomials. All of these are the optimum method for a different given set of conditions.

Much of filter theory goes back to the days of copper conductor telephone circuits around 1920 - 1935.

"Modern" filter theory was invented by Campbell and Darlington of the Bell Telephone Laboratories in this time period.