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FIR Filters - FIR Fundamentals

FIR filters are most widely used in FPGA implementations owing to its linear phase property. Compared to IIR filters, FIR filters have simple and regular structures which are easy to implement on hardwareFIR filters require higher number of taps. | Chapter 10 FIR Filter Fundamentals Digital filters are usually classified by the duration of their impulse response which can be either finite or infinite. The methods for designing and implementing these two filter classes differ considerably. Finite impulse response FIR filters are digital filters whose response to a unit impulse unit sample function is finite in duration. This is in contrast to infinite impulse response HR filters whose response to a unit impulse unit sample function is infinite in duration. FIR and HR filters each have advantages and disadvantages and neither is best in all situations. FIR filters can be implemented using either recursive or nonrecursive techniques but usually nonrecursive techniques are used. 10.1 Introduction to FIR Filters The general form for a linear time-invariant FIR system s output y k at time k is given by N- 1 y k h n x k n 10.1 n 0 where h n is the system s inpulse response. As Eq. 10.1 indicates the output is a linear combination of the present input and the N previous inputs. The remainder of this chapter is devoted to basic properties and realization issues for FIR filters. Specific design approaches for selecting the coefficients bn are covered in Chaps. 11 12 and 13. FIR advantages FIR filters have the following advantages FIR filters can easily be designed to have constant phase delay and or constant group delay. 161 162 Chapter Ten FIR filters implemented with nonrecursive techniques will always be stable and free from the limit-cycle oscillations that can plague IIR designs. Round-off noise which is due to finite precision arithmetic performed in the digital processor can be made relatively small for nonrecursive implementations. FIR filters can also be implemented using recursive techniques if this is desired. FIR disadvantages Despite their advantages FIR filters still exhibit some significant disadvantages An FIR filter s impulse response duration although finite may have to be very long to obtain sharp .