why analog filters are not FIR?

[wajahat]

One difference between analog and digital filter is that digital filter can be FIR.WHY CAN'T an analog filter be FIR?
Any response would be of great help.

 

[flatulent]

Analog filters have response that is a ratio of polynomials. The Laplace transform of these have decaying exponentially which mathematically never reach zero.

 

[wajahat]

flatulent "Analog filters have response that is a ratio of polynomials. The Laplace transform of these have decaying exponentially which mathematically never reach zero."
Thanks flatulent.
Is there any physical reasoning also?

 

[flatulent]

Physiclally, you can think that an input impulse will charge up the capacitors. These will discharge through any resistors. The voltage will decline but the current will also so the decline will become smaller and smaller as time goes on but never reach zero.

 

[basemgergawy]

Mainly, analog filter is designed by op-amp with feedback circuit. Any feedback circuit has transfer function

H(s)= A(s) / 1+B.A(s)

the transfer function is a ratio of two polinomials thats form a IIR filter not FIR