TOP MENUWhat is a digital filter? Difference between FIR filter and IIR filter |
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・Frequency analysis ・Calculate the Fourier transform ・Detrending method ・Sampling theorem ・DC component ・Bilinear transform ・Floating point number ・Resolution, sampling period ・Fixed point number ・Digital Filter ・Octave analysis |
・In Japanese
■What is a digital filter?
Digital filters are used in discrete time systems.
When implementing a filter in an embedded system that requires time to be treated as a discrete system, the continuous time system should be discretized.
For example, the difference between continuous-time and discrete-time low-pass filters is as follows.
■Discretization method
In continuous time, the physical model is expressed as a differential equation, which is transformed into a Laplace transform and replaced with an s-function.
In discrete time, it is necessary to express the differential equation using a backward difference method, etc., and then convert it to Z and replace it with a z function.
There is also a method of approximating the s-function to the z-function using bilinear transformation. ■Types of digital filters
Digital filters include FIR (Finite Impulse Response) filters and IIR (Infinite Impulse Response) filters.
The difference is that FIR filters process using only input values, while IIR filters process using not only input values but also output values.
FIR, which uses only input values, can be said to have a finite response because if the input becomes 0, the output will eventually become 0.
On the other hand, IIR that also uses output values is called an infinite response because the result does not necessarily become 0 even if the input becomes 0.
・It is necessary to remember a lot of past input information, which requires memory capacity. The calculation formula also becomes longer.
・A lot of past input information is not required, and it can be expressed with a simple formula.
■Digital filter operation check
Explained here.
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