Digital filter design method and device, digital filter design program, and digital filter

Abstract

For example, more than one FIR-type basic filters having a symmetric sequence of numbers having a predetermined characteristic as a filter coefficient are combined and connected in longitudinal connection. The filter coefficient is calculated and for the y-bit data of the calculated filter coefficient, the lower bit is cut off for rounding so as to obtain a filter coefficient of x-bit (x < y). Thus, it is possible to significantly reduce an unnecessary filter coefficient without performing the conventional window multiplication. Moreover, it is possible to realize a digital filter having a desired frequency characteristic with a small circuit size and with a high accuracy without causing a truncation error attributed to window multiplication in the frequency characteristic.

Description

technical field [0001] The present invention relates to a design method and device of a digital filter, a program for designing a digital filter, and a digital filter, in particular to a tapped delay formed by a plurality of delayers, and the output signals of each tap are respectively digitalized. The FIR filter and its design method are the type of FIR filter and its design method that are output by adding their multiplication results after being multiplied. Background technique [0002] In various electronic machines provided in various technical fields, some kind of digital signal processing is usually carried out inside them. Among the most important basic operations of digital signal processing, there is filtering processing to extract only signals in a necessary frequency band from an input signal mixed with various signals or noise. Therefore, digital filters are often used in electronic equipment that performs digital signal processing. [0003] Most digital filte...

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Problems solved by technology

[0006] However, since the frequency characteristics of the FIR filter obtained by conventional design methods depend on window functions and approximate expressions, unless these are properly set, the desired good frequency characteristics cannot be obtained.

However, in general, it is difficult to properly set the window function or approximation

In addition, when windowing is performed to reduce the number of filter coefficients, the frequency characteristic will produce a truncation error

Therefore, there is a problem that it is very difficult to achieve the desired frequency characteristics with conventional filter design methods.

[0007] In addition, in order to design an FIR filter that achieves the desired frequency characteristics as precisely as possible, the number of filter coefficients reduced by window selection is very limited

Therefore, the number of taps of the designed FIR filter is very large, and the filter coefficient values ​​are very complex and random

Therefore, there is a problem that a large-scale circuit structure (adder, multiplier) is required to realize the number of taps and filter coefficient values.

Therefore, in the past, it took time and effort for skilled engineers to design, and there was a problem that it was not easy to design an FIR filter with desired characteristics.

However, even if any of these methods is used, the passband of the filter can only be narrowed, and it is impossible to precisely realize frequency characteristics of an arbitrary shape with a small number of taps.

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