Patent ID: 7450660

Claim:
A digital modulation apparatus for subjecting in-phase component data and quadrature component data to quadrature modulation and producing output with a predetermined output frequency, the apparatus comprising: a first filter for performing bandwidth limitation on the in-phase component data using a first sampling frequency, which is an integral multiple of a symbol frequency of the in-phase component data; a second filter for performing oversampling on data outputted from the first filter using a second sampling frequency, which is an integral multiple of the first sampling frequency; a first interpolation section for interpolating data outputted from the second filter so that resulting data will have the predetermined output frequency; a third filter for performing bandwidth limitation on the quadrature component data using the first sampling frequency, which is an integral multiple of a symbol frequency of the quadrature component data; a fourth filter for performing oversampling on data outputted from the third filter using the second sampling frequency, which is an integral multiple of the first sampling frequency; a second interpolation section for interpolating data outputted from the fourth filter so that resulting data will have the predetermined output frequency; and a quadrature modulation section for subjecting data outputted from the first interpolation section and data outputted from the second interpolation section to digital quadrature modulation, and outputting resulting data, wherein each of the first sampling frequency and the second sampling frequency is at least a sampling frequency derived from the predetermined output frequency by performing digital frequency division in a regular or irregular manner, and using a frequency ratio or frequency dividing ratio between the second sampling frequency and the predetermined output frequency, a number of samples between a sampling stop point in the second sampling frequency as compared to the predetermined output frequency and a next sampling stop point, and a position relative to the sampling stop point, each of the first interpolation section and the second interpolation section converts the second sampling frequency to the predetermined output frequency, and produces interpolated output based on the predetermined output frequency.