Difference Between FIR Filter and IIR Filter

TYPES OF DIGITAL FILTER

Digital filters are of two types. Finite Impulse Response Digital Filter & Infinite Impulse Response Digital Filter

DIFFERENCE BETWEEN FIR FILTER AND IIR FILTER

FIR Digital Filter

1. FIR system has finite duration unit sample response. i.e h(n) = 0 for n<0 and n ≥ M Thus the unit sample response exists for the duration from 0 to M-1.

2. FIR systems are non recursive. Thus output of FIR filter depends upon present and past inputs.

3. Difference equation of the LSI system for FIR filters becomes 

4. FIR systems has limited or finite memory requirements.

5. FIR filters are always stable

6. FIR filters can have an exactly linear phase response so that no phase distortion is introduced in the signal by the filter.

7. The effect of using finite word length to implement filter, noise and quantization errors are less severe in FIR than in IIR.

8. All zero filters

9. FIR filters are generally used if no phasedistortion is desired.

Example:

System described by

Y(n) = 0.5 x(n) + 0.5 x(n-1) is FIR filter.

h(n)={0.5,0.5}

IIR Digital Filter

1. IIR system has infinite duration unit sample response. i. e h(n) = 0 for n<0 Thus the unit sample response exists for the duration from 0 to ∞.

2. IIR systems are recursive. Thus they use feedback. Thus output of IIR filter depends upon present and past inputs as well as past outputs

3. Difference equation of the LSI system for IIR filters becomes 

4. IIR system requires infinite memory.

5. Stability cannot be always guaranteed.

6. IIR filter is usually more efficient design in terms of computation time and memory requirements. IIR systems usually requires less processing time and storage as compared with FIR.

7. Analogue filters can be easily and readily transformed into equivalent IIR digital filter. But same is not possible in FIR because that have no analogue counterpart.

8. Poles as well as zeros are present.

9. IIR filters are generally used if sharp cutoff and high throughput is required.

Example:

System described by

Y(n) = y(n-1) + x(n) is IIR filter.

h(n)=an u(n) for n≥0