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Instabuility inside a system is caused by poles laying outside of unity circle.
Fir filter itself have no poles at all (only zeros). It is absolutely stable.
But inside of system with feedback, changing fir filter coefficients of course can move system poles to outside of unit circle and can cause instability.
Are you asking about influence of FIR filter to your system?
Hi
Smileysam agree with u.
reason fir filters are just a differential equation
with no denominator which provide the poles.
no denominator no poles no instability
all zero filters.
anyone correct me if i am wrong
ya. actually what will be the response of a signal when passed through an fir filter and the same signal through an iir filter??? are fir filters practically realizable??
thanking you,
AMRITH.S.
vadkudr said:
Instabuility inside a system is caused by poles laying outside of unity circle.
Fir filter itself have no poles at all (only zeros). It is absolutely stable.
But inside of system with feedback, changing fir filter coefficients of course can move system poles to outside of unit circle and can cause instability.
Are you asking about influence of FIR filter to your system?
amriths04 I am sure that FIR filters are practically realizable.But I am not quite sure how it is done.So any help from anyone will be of a great use for me.
amriths04,
It's not possible to compare the responses in general. What you can do is design an iir filter to meet a set of specifications. The design a fir filter to meet the same specifications. The compare the frequency and time domain responses.
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Yes iir filters are realizeable. A common method of design is to design an analog "prototype" filter. Then transfor the analog design by using a transform such the impulse invariant transform, step invariant transform, or bilinear z transform.
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It is also possible to design an iir filter with an arbitrary frequency response by using numerical optimizations methods.
Regards,
Hi friends
one clarification is tat both FIR and IIR filters are realizable
u have many structures like DF1 DF2,cascade parallel,lattice and many more in IIR and in FIR als u have DF structures but the structure depends on whether ur N is odd or even and also linear phase or not.
for the same specifications an IIR is less ordered than FIR(if IIR is 6 FIR may be in 50 - 70)but IIR may lead to instability and it's difficult to achieve linear phase in IIR filters.
But FIR filter doesnt have a pole, this is not agreeable,
FIR filter has a pole, and all its poles lie on the zero.....
and, FIR filter is said to be stable, if the impulse response of that system is symmetric or antisymmetric w.r.t midpoint, else its not stable.
text2babu,
It is true that the FIR filter has no poles, since it consists of weighted delayed sums of the input samples. However, the FIR filter can be designed to have desired properties, Low Pass, High Pass, etc.
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It is also true the FIR filters are always stable. However, IIR filters can be designed to be stable. The only requirement is that the poles of the IIR filter all lie within the region of convergence, e.g., a circle of radius one for normalized filters.
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The symmetry requirements that you mention are criteria for phase linearity, not stability. FIR filters are stable regardless of this symmetry property.
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See any book on DSP for further details.
Regards,
Kral
fir is not instable. fir is finite impulse and IIR is infinite so the fir works on firnite impulse which does not have a feed back and iir is having feed back. fir is more stable than iir.
A discrete system is said to be an FIR system if its impulse response has zero-valued samples for n > M > 0
Integer number M is called the Length of the impulse response
IIR system is a discrete system with an infinite impulse response
FIR = Finite Impulse Response IIR = Infinite Impulse Response
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