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It is easy to achieve the lower decimation rate. L-1 when the decimation rate is N0, how can we obtain the filter coefficients when n is not equal to N0 through the set of reference coefficients H (n)? Assuming that the filter coefficients H (n), n = 0,1,2. It can be seen from section 2 that the down decimation rate n is inversely proportional to the filter cut-off frequency, directly proportional to the stopband attenuation and directly proportional to the filter length. Theoretically, variable parameter filters can not be realized with only one set of filter coefficients. Selecting a group of appropriate filter coefficients can complete the filtering of various lower decimation rates.įilter coefficients determine filter characteristics. The method used in this section avoids this situation. Due to the change of extraction rate, there will be many such tables, which will consume a lot of storage space.
#Low pass filter designer online Pc
The usual way is to calculate the coefficient on the PC and make it into a look-up table. If the filter coefficients are calculated after the cut-off frequency is obtained, it will bring a lot of computation, because IFFT (inverse Fourier transform) is performed for each group of filter coefficients. From the design flow of FIR filter, the filter coefficient will change with the change of cut-off frequency.
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When the decimation rate changes, the filter parameters will change, and the filter must be redesigned. It can be seen from section 2 that the filter characteristics in oversampling are determined by the resolution and down decimation rate of the ADC itself. The type of filter is FIR filter, and its order is directly proportional to the down decimation rate.ĭesign of variable parameter low pass filter Where, M is the oversampling rate, n is the down decimation rate, B is the original resolution of ADC, B0 is the improved resolution, n = 4B0, and usually there is. The filter parameters that the oversampling technology can perfectly achieve its goal meet: passband cut-off frequency, passband attenuation RC = - 3dB, stopband cut-off frequency, and stopband attenuation required to filter quantization noise is The low-pass filter of oversampling technology should complete the functions of quantization noise filtering and anti aliasing filtering during downsampling at the same time. Low pass filter in oversampling Technology
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Therefore, it is necessary to design a low-pass filter with variable parameters to meet this demand. However, in many applications, a variety of signals need to be measured, and the data acquisition part must have adaptive characteristics, that is, the lower decimation rate can be selected independently according to the frequency band of the input signal, and the characteristics of the low-pass filter should also change after oversampling. Without this filter, oversampling can not produce any effect. Ī key link of oversampling technology is the low pass filter (LPF) after sampling. Therefore, it is widely used in the field of measurement and control by digital signal processing practitioners. Oversampling technology not only does not add additional analog circuit, but also improves the effective resolution and simplifies the analog circuit, which is simple and easy. It improves the signal-to-noise ratio of ADC by reducing quantization noise. "Oversampling technology is one of the methods often used by digital signal processors to improve the performance of analog-to-digital converter (ADC).