| 摘要 |
PURPOSE:To reduce the capacity of a storage circuit to half by storing only filter coefficients corresponding to a half of the impulse response sequence of a linear phase infinite impulse response digital filter by utilizing the symmetry of the impulse response sequence, and reading them by using a reversible counter. CONSTITUTION:The storage circuit 1 is stored with N pieces of input data X(0)...X(N-), which are ORed with coefficient data H(0)...H(M) in the storage circuit 2 by the time when next new input data are supplied. When a filter degree N is odd, the reversible counter 3 is set to the address A of the coefficient data H(0) and then counts up, one by one, in synchronism with the circulation of data in the storage circuit 1. Thus, the coefficient data H(0)...H(M) are read out successively in order. When the reversible counter 3 counts up to the address (A+M) of the coefficient data H(M), a control circuit 4 generates a specification output for down mode and then the reversible counter 3 begins to count down. Consequently, the coefficient data H(M-1)...H(0) are read out reversely in order. Thus, the coefficient data are supplied to a multiplier 5 in the order of H(0), H(1)...H(M-1), H(M), H(M-1)...H(0). |
