JPS5720012A - Band-pass filter - Google Patents

Abstract

PURPOSE:To obtain resonance characterisitcs of a BPF, obtained by connecting an LPF and an HPF, without increasing the capacity of an ROM by giving amplitude characteristics a peak by increasing or decreasing some of coefficients of a transfer function. CONSTITUTION:In the ROMs 6' and 16' of an LPF and an HPF, coefficients b1 and b2 which correspond to cutoff frequencies are stored. A coefficient KL to be supplied to multipliers 9 and 19 is calculated by arithmetic circuits 10a and 10b by using output coefficients b2n and b2m of arithmetic circuits 10a and 10b. The circuits 20a and 20b calculate the coefficients b2n and b2m by the coefficient b2. In the LPF, adders 1 and 2 subtract and add coefficients from and to an input signal, and the multiplier 9 multiplies the result by KL to send an output to the HPF. In the HPF, adders 11 and 12 subtract and add coefficients from and to the output of the LPF, and the multiplier 19 multiplies the result by KL to obtain an output signal from the BPF. According to combinations of logical levels of control signals (n) and (m) supplied to the circuits 20a and 20b, the depth of the resonance level of the BPF is controlled.