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Difference between Infinite Impulse Response (IIR) & Finite Impulse Response (FIR) filters

Infinite Impulse Response Filters (IIR)

Finite Impulse Response Filters (FIR)

All the infinite samples of the impulse response are considered in the designing of IIR filters. Only N samples of the impulse response are considered in the designing of FIR filters.
The construction of an IIR filter involves designing an analog filter first for the desired specifications and then converting it into a digital IIR filter. The construction of an FIR filter with the desired specifications can be done directly using certain methods (like windowing).
Thus we can say that IIR filters have an analog equivalent. Thus we can say that FIR filters don’t have an analog equivalent.
The IIR filter requires past output samples in addition to current and past inputs to obtain its current outputs. The FIR filter requires only past and current inputs to obtain its current output. They don’t care about past outputs.
An IIR filter’s design specifications only specify the desired characteristics of its magnitude response. An FIR filter’s design specifications specify both, the magnitude as well as the phase response.
Physically realizable infinite impulse response filters don’t have linear phase characteristics. Physically realizable FIR filters can be designed with linear phase characteristics easily.
IIR filters are recursive FIR filters are non-recursive. However, it is possible to design recursive FIR filters too.
The transfer functions of infinite impulse response filters have both poles and zeros. The transfer functions of finite impulse response have only zeros.
IIR filters are/have LESS:

  • Powerful: In terms of computational prowess.
  • Power-hungry: In terms of power supply.
  • Stable
  • Memory
  • Time to set up
  • Delay
FIR filters have/are MORE:

  • Power
  • Power-hungry
  • Stable
  • Memory
  • Time to setup
  • Delay
IIR filters are/have MORE:

  • Filter coefficients
  • Tweakable on the fly
  • Efficient
  • Sensitive
  • Easy to use
FIR filters have/are LESS:

  • Filter coefficients
  • Tweakable on the fly
  • Efficient
  • Sensitive
  • Easy to use
IIR filters are used in Band Stop and Band Pass filters. FIR filters are used in Anti-aliasing, low pass, and baseband filters.
IIR filter bloack diagram - FIR vs IIR FIR filter bloack diagram - FIR vs IIR

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