| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide an IIR type digital filter which can secure desired filter characteristics and also can secure satisfactory filter characteristics even in a low level input mode by applying an arithmetic operation to the digital input data based on a filter coefficient that is previously set. SOLUTION: The N-bit input and output data are referred to as X and Y with the N-bit filter coefficients referred to as a0, a1, a2, -b1 and -b2 and the data of lower N bits on the multiplication result of feedback terms referred to as Z respectively. Then the filter characteristics are secured in an n-sample mode by a differential equation, i.e., Y (n)=a0*X(n)+a1*X(n-1)+a2*X (n-2)-b1* Y(n-1)+Z(n-1)}-b2* Y(n-2)+Z(n-2)}. The multiplication of the data on Z(n-1) and Z(n-2) are carried out by the multipliers 16 and 17. In other words, the lower 1-word data 18 of the output data Y (n) are sent to a delay unit 14, and the higher 1-word data 19 are sent to a delay unit 5 respectively.</p> |
