Filter classification

Classified by signal processing type

Filters can be divided into two categories: analog filters and discrete filters. Among them, imitation filters can be divided into three categories: active, passive, and heterogeneous; Discrete filters can be divided into three categories: digital, sampling analog, and hybrid. Of course, each category can be further divided, in short, their categories can form a tree structure.

Filter - Filter Type

Butterworth Response (Flatest Response)

Butterworth imaging can maximize the passband flatness of the filter. The image should be very flat, close to the DC signal, and gradually attenuate to the cutoff frequency point of -3dB, eventually approaching an attenuation rate of -20dB/decade, where n is the order of the filter. Butterworth filters are particularly suitable for low-frequency applications and are crucial for maintaining gain flatness.

Bessel correspondence

In addition to altering the roughness of frequency dependent input signals, filters also introduce a delay. Delay causes distortion of non sinusoidal signals based on frequency phase shift. Just as Butterworth imaging maximizes the roughness of the passband, Bessel imaging minimizes the phase nonlinearity of the passband.

Chebyshev Care

In some applications, the most important element is the speed at which the filter blocks unnecessary signals. If you can accept some ripple in the passband, you can achieve faster attenuation than a Butterworth filter. Appendix A contains a table of required parameters for planning up to 8 orders of Butterworth, Bessel, and Chebyshev correspondence filters. Two tables are used for Chebyshev response: one for 0.1dB maximum passband ripple; Another one is used for 1dB maximum passband ripple.

Filter - Filter Planning

The special power of filters can be described by their frequency response, and according to their different characteristics, they can be divided into low-pass filters, high pass filters, band-pass filters, and band stop filters.

The skill guidelines used to illustrate the function of filters primarily include:

Center frequency f0, which is the center of the operating frequency band

Bandwidth BW

Passband attenuation, i.e. the maximum attenuation within the passband

stop-band attenuation

Regarding practical filters, considering that the quality factor of the components in practice is a finite value (due to limitations in material and process levels), all useful filters in engineering are lossy filters. Therefore, the minimum penetration attenuation within the passband should also be considered for these filters.

Modern filter planning is often accomplished through the use of filter conversion methods. The first step is to obtain a new policy filter by frequency conversion and impedance conversion of the low-pass prototype filter.