| 摘要 |
PURPOSE:To realize a low pass filter whose characteristic is a rising characteristic nearly at f0/2 and attenuated steeply at f0/2 or over through simple element constitution by constituting the titled filter for decoding a D/A-converted signal and acting at a frequency twice the sampling frequency f0 by means of a special function. CONSTITUTION:The filter is constituted by using a function tn=Xn+(xn-1+xn+1) sin(pi/2)/(pi/2)+SIGMAxksin[pi(n-k)/2]/[pi2<n-k-1>]+SIGMAxksin[pi(k-n) /2]/[2<k-n-1>-], where Xk is an input signal tn is an output signal, n is an integer, k is a frequency being 1/2 of the sampling angular frequency, and two summations are adopted for k=n-2, n-3..., n-m and k=n+2, n+3,..., n+m respectively. In case of 16 bits, 31 stages of registers retarding the time corresponding to one angular frequency are enough and they are represented in captions R in figure. A multi plier (caption M) is connected respectively to an odd number order register. Each multiplier has a magnifying power corresponding to each coefficient of the said function. Thus, in inputting the output of each multiplier to an adder A and extracting its output, the filter of the above constitution is realized.
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