Minimum Order of FIR Filter

[bhq]

Usually FIR filter have high order ie a lot of poles placed at z=0. But FIR is always stable.

FIR is difficult to implement because of high order as compared with IIR.

What is the minimum order of FIR to be implemented with it ??

 

[senaydud]

May I ask you something? Why do you think that poles-at-zero makes FIR difficult to implement?

 

[bhq]

I believe that in FIR there are too many poles placed at z=0. and are of higher order. ie large number of ploes are at same location. thats the reason that they are difficult to implement.

Please give me your point of view.

 

[senaydud]

May be I should read some on FIR filters, but to me; if the poles are at zero then that means there are no poles to implement lets say you have a filter like : 1+2z-²+5z-³. That is a filter where the poles are all at zero, init? So its easy to implement; Take a couple of delay elements, dont forget to take the weights into account and thats it.
I may not be right because I havent read anything about filters, so could you tell me a reference where it says the FIR with all poles at zero is not easy to implement?

 

[FvM]

The only difficult thing with FIR filters is the availability of required resources to my opinion. Apart from that, they are easy to implement. The minimum order depends on intended filter characteristics and relative sampling rate fc/fs as well. Thus a simple FIR filter may require a high order for fs >> fc.

 

[senaydud]

May I ask something, what is fc and fs? fs is the sampling frequency I guess, but what is fc?

 

[sajjadi335]

Well, fc is cut frequency of the filter.

The most important thing is you gain phase linearity in FIR filters, at the cost of larger degree. Besides, they're so easily implemented with Multiply and Accumulate blocks and a Tapped Delay Line. They are feedforward and that makes their implementation so easy, and also stable.

 

[intelnside]

ar, one question , how do we decide the cutoff frequency for FIR filter?

is it based on the infomation that we wan to filter it?

 

[Kral]

bhq,
See the article "A New Estimation Formula for Minimum Filter length of Optimum FIR Digital Filters".
ieeexplore.ieee.org/iel4/5224/14216/00652198.pdf
You must be an IEEE member to download this article.
Regards,
Kral

 

[xulfee]

it is simple,no need to worry about order