Hi
I want to know what does notch filter depth shows? On what parameters does the depth depend on? I think more deeper response is better.
An ideal 2nd-order notch filter has zero gain at the notch frequency wz. Here, wz is the zero frequency of the transfer functions numerator.
An ideal notch filter with equal gain values for very low and very high frequencies requires the condition
wz=wp. The frequency wp is the pole frequency (zero of the denominator).
More than that, similar to the bandpass case, a second-order notch can have different Qp values, which are responsible for the slope of the transfer function for frequencies smaller and larger than wz.
(Comment: There is no phase shift of 180 deg at the notch frequency).
Notch filter transfer function:
H(s)=N(s)/D(s)
N(s)=A[1+(1/wzQz)+(s²/wz²)]
D(s)=[1+(1/wpQp)+(s²/wp²)]
For
Qz approaching
infinity we have a real zero on the imaginary axis (ideal notch). The pole quality Qp determines the steepness of the function in the vicinity of the notch at wz.
Of course, due to some uncertainties and tolerances it is not possible to have an infinite Qz
- this "error" determines the achievable depth of the notch.