• Resolved

TINA/Spice: stability analysis of sallen-key high pass filter

Tool/software: TINA-TI or Spice Models


I'm designing a sallen-key high pass filter as below, the output is instable.

So I analyze the stability of this circuit using the following circuit.

The bode plot of Aol*beta is:


At frequency of 12Hz, there is a pole, why the frequency shift is up to 300 degree? My basic knowledge is that a pole may result in 90 degree phase shift, is that wrong? Besides, the slope at 0dB is -20dB/dec, why the circuit is instable? 

Thank you!