DIGITAL SIGNAL PROCESSING-TYPE DIGITAL MODULATION DEVICE

摘要

PROBLEM TO BE SOLVED: To correspond to an arbitrary carrier frequency without the need of a high speed digital element by generating plural bands becoming high from a base band at every prescribed frequency, permitting a complex band pass filter to pass through only the band containing the desired carrier frequency and obtaining the analog signal of the desired carrier frequency. SOLUTION: The input signals of Ich and Qch are made to pass through the base band filters 122 and 125. A modulated frequency exp (jωct) and exp (jωct+jπ/2) are multiplied. The sum is enlarged to 120 MHz at every 20MHz in an interpolation IP130 and only the band near fif is selected by a complex coefficient BPF 131. The real part is changed to the analog signal in a D/A converter 133 and LPF 134 removes an image component and takes out the part of fif. A modulated frequency fc is fif-n.f symb and it is lower than f symb. Thus, the speed of a peripheral digital element can be slow and cost can be reduced.