| 摘要 |
PURPOSE:To make it possible to vary continuously he Q and gain of a filter by determining the Q so that real-axis and immaginary-axis projection values at two zero points satisfy a specific value and by determining the gain at the center frequency of filter characteristics on the basis of the ratio of both the projection values. CONSTITUTION:With regard to the digital filter, the pole and zero point of Laplace transform type biquadratic transfer function Hs are positioned at the same circle in plane S and the radius of the circle is determined as the central angular frequency of filter characteristics. Then, the real-axis projection value and immaginary-axis projection parts as to two poles in plane S are denoted as sigma1 and omega1, and real- axis projection value and immaginary-axis projection value at two zero points as sigma2 and omega2. In this case, Q of filter characteristics is so determined that while (i) is made equal to one or two, sigma1=omega1/2Qi.omegai=(omegai/2Qi)<2>-omegai<2>]<1/2>. From ratio sigma<2>/sigma1 of real-axis projection value sigma1 of the pole in plane S to real-axis projection value sigma2 at the zero point, the gain at the center frequency of filter characteristics is determined to constitute the filter of fixed characteristics. |
