filter response

[aamir1]

HI guyz !!what is the significance of zeroes in the response of filter ??? after a pole the filter response gets decrease by a roll off but what a zero does???

 

[Winterstone]

Aamir1, filter circuits without zeros (so called "allpol filters") have a numerator N(s) of the transfer function that consists NOT of a polynomial (just a constant or an expression involving "s").

However, there are some filter functions (Chebyshev/invers, elliptical/Cauer, allpass filter) that require a polynomial in N(s). This polynomial creates the zeros.

 

[aamir1]

but what is the significance of zero what does this zero do in the transfer function what changes will it make

 

[Winterstone]

For some filter functions (Chebyshev invers and elliptical) the zero causes the magnitude of the transfer functions to be zero at a certain frequency.
The same applies to all notch filters because it is their main task to make the output voltage to disappear at one frequency.
That`s obvious, is it not?

In case of allpass filters we have a zeros in the RHP which mirrors the pole distribution in the LHP.
Thus, the magnitude is constant over the frequency and only the phase is frequency dependent. This is the main task of allpass filters.