| 摘要 |
PURPOSE:To reduce the operation speed of a circuit composing a digital filter and to integrate the circuit with high economization by using the digital filter of which amplitude characteristic and frequency characteristic are symmetically situated by setting the 1/4 point of sampling frequency as the center. CONSTITUTION:A digital FM modulator 105 which modulates a first signal and outputs a first FM signal, a first digital filter 106 which makes the first FM signal as input, reduces the frequency band of a second signal and of which amplitude characteristic and frequency characteristic are symmetically situated by setting the 1/4 point of the sampling frequency as the center, a digital mixer 107 which adds and mixes the output of the first FM signal and the second signal with a prescribed mixture ratio and outputs a third signal, a DA converting means 108 which converts the digital quantity of a third signal to analogue quantity and a recording means 109 which records the signal from the DA converting means on a recording medium are provided. Therefore, are the digital filter is used as a feedback loop more than two order, the completion of the arithmetic operation within a sample clock term is satisfactory. Thus the operation speed can be sharply reduced.
|
