The low-pass filter is an electron filtering device that allows signals below the cut-off frequency to pass through, but higher than the cut-off frequency of the signal can not pass.
For different filters, the intensity of each signal is different. When used in audio applications, it is sometimes referred to as a high frequency shear filter, or a treble cancellation filter.
The low-pass filter concept has many different forms, including electronic circuits (such as the hiss filter used in audio equipment), digital algorithms for smoothing data, acoustic barriers, blurring of images, etc. Both tools are By removing short-term fluctuations, retaining long-term trends provides a smooth form of the signal.
The role of low-pass filters in signal processing is equivalent to the role of other areas such as moving average in the financial sector;
There are many kinds of low-pass filter, of which the most common is the Butterworth filter and Chebyshev filter.
The Butterworth filter is a design classification of the filter, which uses a Butterworth transfer function, such as high pass, low pass, bandpass, band impedance and other filter types.
The Butterworth filter has a smooth amplitude-frequency characteristic both inside and outside the passband, but with a longer transition zone, it is easy to cause distortion in the transition zone.
Chebyshev filter is a design classification of the filter, which uses the Chebyshev transfer function, but also high-pass, low-pass, band pass, high impedance, band resistance and other filter types.
The low-pass filter allows signals from DC to a cutoff frequency (fCUTOFF) to pass through. The high-pass and band-pass coefficients of the second-order transfer function of the general filter are set to zero, that is, a second-order low-pass filter transfer formula is obtained:
For frequencies above f0, the signal drops at the square of the frequency. At the frequency f0, the damping value attenuates the output signal. You can cascade multiple of these filters to get a higher order (more steep) filter. Assume that the design requires a four-order Bessel low-pass filter with a cutoff frequency of 10 kHz. According to reference 1, the frequency of each part is 16.13 and 18.19 kHz, respectively, and the damping values are 1.775 and 0.821 respectively, and the high pass, bandpass and low pass coefficients of the two filter divisions are 0, 0 and 1 respectively. You can use these two filter sections with the above parameters to implement the required filter. The cutoff frequency is the frequency point at which the output signal attenuates by 3 dB.
Wave circuit is to allow a certain frequency range of the signal through, and to prevent or weaken the other frequency range of the signal. The active filter circuit consists of resistors, capacitors, and integrated operational amplifiers, also known as active filters. Active filter can filter at the same time can also play a role in the signal, which is passive filtering can not do. According to the filter circuit through or to prevent the signal frequency range is different, the filter circuit can be divided into low-pass, high-pass, band-pass with resistance circuit. This article discusses the design and simulation of active low-pass filter circuits. The active low-pass filter circuit can suppress or attenuate high-frequency signals through low-frequency signals.