What is the Difference Between FIR and IIR?

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FIR (Finite Impulse Response) and IIR (Infinite Impulse Response) filters are two types of digital filters used in signal processing. The main differences between them are:

  1. Impulse Response: The impulse response of an FIR filter is finite, meaning it has a definite duration, whereas the impulse response of an IIR filter is infinite, meaning it continues indefinitely.
  2. Causality: FIR filters are causal, meaning their output depends only on present and past input samples. In contrast, IIR filters are non-causal, meaning their output depends on both present and future input samples.
  3. Stability: FIR filters are always stable, as their impulse response does not cause any unstable behavior. However, IIR filters can become unstable if their feedback path has a gain greater than one.
  4. Design: FIR filters can be designed purely by trial and error, and their design process remains the same, regardless of the application. IIR filters, on the other hand, require more theory and design considerations.
  5. Analog Components: IIR filters can have analog components, while FIR filters do not.
  6. System Complexity: IIR filters generally require more multipliers than FIR filters, making FIR filters less complex.

In summary, an FIR filter is non-recursive (all constants are zeros except for the last one), causal, has a finite impulse response, and is more complex than an IIR filter. An IIR filter is recursive, non-causal, has an infinite impulse response, and is less complex than an FIR filter.

Comparative Table: FIR vs IIR

FIR (Finite Impulse Response) and IIR (Infinite Impulse Response) are two types of filters used in signal processing. Here is a table highlighting the main differences between them:

Feature FIR (Finite Impulse Response) IIR (Infinite Impulse Response)
Definition FIR filters are linear, static systems with a finite impulse response to any input. IIR filters are recursive, dynamic systems with an infinite impulse response to any input.
Stability FIR filters are always stable, as they do not rely on feedback. IIR filters can be unstable, as they rely on feedback and can experience oscillation.
Structure FIR filters have a linear, lattice, or conjugate structure. IIR filters have a recursive structure that depends on the output of the filter itself.
Design FIR filters are easier to design and analyze due to their linear nature. IIR filters are more complex to design and analyze, as they involve recursive equations.
Frequency Response FIR filters can achieve higher stop-band attenuation but have a longer settling time. IIR filters can provide better frequency selectivity but may have higher group delay.
Applications FIR filters are commonly used in digital signal processing, telecommunications, and control systems. IIR filters are often used in audio signal processing, digital filters, and feedback systems.

In summary, FIR filters are linear and stable, making them easier to design and analyze, while IIR filters are recursive and potentially unstable, requiring more complex design and analysis techniques. Both types of filters have their advantages and are used in various applications depending on the specific requirements of the system.