# Can you help me understand this transient output of this universal biquad filter? My Bode plot proves that the filter is working perfectly [closed]

I am designing a universal biquad filter in LTSpice and ASLK Pro board with a square wave input:

I have taken the Q factor as 1. I'm not convinced it is right. Is it as simple as the ratio of RQ/R6? I verified this in the magnitude response of BS, Q = fc/BW, where I got approximately 0.98.

The problem I am facing is that, when my Q=1, all the resistors are equal, the transient response looks like this, it doesn't complete the full cycle.

How does this affect the working of a biquad filter? The Bode plot shows a proper working condition and my notch is quite steep at -50 dB.

Why does the notch value reduce as my RQ value increases? Shouldn't it be the notch value increases as my RQ increases?

I also have another doubt regarding the waveform in the transient analysis. This is at Q=2.91 (verified with Bode, I calculated the BW for fL and fH at -3 dB). Why does the high pass filter have that extra rise? How does this get filtered output in the bandpass integrator?

The same happens when the value of RQ is 1.61k. There is a rise at the rising edge and it exceeds the square wave input:

An underdamped response reaches stable state soon, a critical damped response has ringing and takes longer to reach stable state, so which damping is preferred to have in a filter?

I am a student and I am quite new to these topics, please bear with me. It would be super helpful to get a few answers.

• I’m voting to close this question because the OP wants a discussion and is asking open-ended questions Commented Jul 10 at 7:39
• "Bode plot" is not a "transient plot". It is obvious that with square wave input, you should have some "rise" in the HPF output ... Commented Jul 10 at 8:23