| 摘要 |
PURPOSE:To reduce memory capacity for coefficient storage in a digital filter device which is variable in cut-off frequency, by approximating at least one of coefficients of a transfer function to a straight line, polygonal line or curved line. CONSTITUTION:Coefficient b1 supplied to multiplier 4 is -2+fcX2<-2> (where fc is a cut-off frequency). Logic circuit 10 is provided to multiplier 4. Here, frequency fc is 14-bit data consisting of four bits above the decimal point and ten bits below the decimal point, and its unit is ''kHz''. Therefore, frequency fc is 16kHz at a maximum and the minimum range of frequency fc is 2<-10>kHz. For the arithmetic, 14-bits data is shifted to right by two bits and [-2] is added. On the other hand, ROM6' is stored with coefficient b2 to multiplier 8 and coefficient (k) of multiplier 9. |
