Practical Issues of FIR and IIR Filters

practical application of iir

Hi

I did MTech in DSP. I know how to build FIR and IIR filters. But yesterday my superior asked me some simple questions regarding these filters. Can you please help me in this regard ?

1. What are the practical applications of FIR and IIR filters? And give me the examples two for each.

2. On what basis, do we have to select the filter type (whether FIR or IIR) for a perticular application.

I hope I will get the reply soon from any intelligent.:|

Thanks,
Vishwa

comparison of fir and iir filters

Hi you can find a practical view in the free book:
The Scientist and Engineer's Guide to Digital Signal Processing

hxxp://www.dspguide.com/pdfbook.htm

practical applications of iir filters

Vishwa,

1. What are the practical applications of FIR and IIR filters? And give me the examples two for each.

Click to expand...

Practical applications of FIR filters are Anti-Aliasing, Low-Pass, Reconstruction or Baseband filters that are less demanding to design and implement, robust and low-cost. Usually less than 3 or 5 orders/taps.

Practical applications of IIR filters are Notch, Band-limiting, Noise-Shaping or higher order filters. In simple analogy, a high order FIR filter can have its processing effort and component count greatly reduced by using an IIR filter.

2. On what basis, do we have to select the filter type (whether FIR or IIR) for a perticular application.

Click to expand...

FIR is always stable, which is why it is a rule of thumb to first implement a design with FIR to first check if the eventual frequency shaping can be achieved before advancing to IIR filter which will incur more design effort.

All recursive/iterative/feedback structure has stability issues to be carefully taken of. All poles must be conjugated to ensure stability and it usually quite difficult to match the conjugate with a good coefficient in actual implementation due to bitwidth of the digital filter you will implement. Therefore IIR has this issue which usually hit designers.

Another shortcoming of IIR filter is that the structure is recursive which implies increased complexity of the structure and more coefficients that must be properly selected. Such problem is easily taken care of with FIR filters which has much simpler structure and less coefficients.

From low power design point of view, which is getting extremely important these days in portable electronics, IIR filter incurs more power consumption since it requires more coefficients to be stored in memory and more processing variables involved, FIR is favourably used in low power applications instead. You may read IEEE ISSCC Journals between 2003 to 2005 that discussed greatly emphasis on FIR filters over IIR filters for ultra-low-power designs.


PhD MSc DIC BEng (Hon)
Analog Devices Inc (Ireland)