IIR filter and FIR filter

Table of Contents

1. Analog filter and digital filter

2.Impulse Response

3.IIR(Infinite impulse response)&FIR(Finite impulse response)

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1. Analog filter and digital filter

Using analog circuits to directly process analog signals to form analog filters, so it is a continuous time system, such as intermediate frequency or radio frequency communication circuits;

Using the discrete time system to filter the digital signal (time domain discrete, amplitude value quantization) constitutes a digital filter.

Of course, digital filter processing can also be used after sampling and processing of analog signals, and compared with analog filters, digital filters are easier to implement, and have higher stability, accuracy, reliability, and cost-effectiveness. Therefore, digital filtersFilter applications continue to become widespread.

2.Impulse Response

When the input of a system is an impulse function, its output is the impulse response.As shown in the figure below, where h(t) is the impulse response:

 

3.IIR(Infinite impulse response)&FIR(Finite impulse response)

(1) IIR (Infinite Impulse Response) digital filter

As the name implies, when the input is an impulse function, the output impulse response h[n] (because it belongs to a digital filter, the independent variable becomes n) can be extended infinitely.

(2) FIR (finite impulse response) digital filter

When the input is an impulse function, the output impulse response h[n] can end in a finite length of time.

The main reason for this phenomenon is that the IIR-type filter adopts a recursive structure, that is, there is a loop back in the structure to form a feedback branch to continuously generate input for infinite output; in contrast, FIR filterThe implementation of the controller is relatively simple, and there is no feedback part in its structure, so its impulse response is limited.The difference between the two can be easily seen from the difference equation and structure diagram in the following figure:

Because the feedback of the IIR filter is difficult to adjust, it is easy to cause vibration (such as howling in the microphone), and the FIR filter does not have the influence of feedback adjustment, so the FIR filter is more stable.The nonlinear phase characteristics of the IIR filter make it generally only used in some occasions that are not sensitive to phase, such as voice communication, while the FRI filter can be used in some transmission systems that require phase, such as image processing.