Table of contents
1. Analog filter and digital filter
3.IIR(Infinite impulse response)&FIR(Finite impulse response)
1. Analog filter and digital filter
Using analog circuits to directly process analog signals constitutes an analog filter, so it is a continuous time system, such as intermediate frequency or radio frequency communication circuits, etc.;
A digital filter is formed by using a discrete time system to filter a digital signal (discretization in the time domain, quantization of the amplitude value).
Of course, digital filters can also be used after sampling and processing analog signals, and compared with analog filters, digital filters are easier to implement, and have higher stability, accuracy, reliability, and cost performance. 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) type 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 amount of time.
The main reason for this phenomenon is that the IIR filter adopts a recursive structure, that is, there is a loop in the structure to form a feedback branch to continuously generate input for infinite output; in contrast, the FIR filter realizes The relatively simple, there is no feedback part in its structure, so its impulse response is limited. The difference between the two can be easily seen through the difference equation and structure diagram in the figure below:
Since the feedback of the IIR filter is difficult to adjust, it is easy to cause oscillations (such as howling in the microphone), while the FIR filter does not have the influence of feedback adjustment, so the FIR filter is more stable. The nonlinear phase characteristic of the IIR filter makes 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.