Modulator and modulation method for orthogonally modulating digital baseband signals

摘要

PCT No. PCT/JP98/00657 Sec. 371 Date Sep. 28, 1998 Sec. 102(e) Date Sep. 28, 1998 PCT Filed Feb. 17, 1998 PCT Pub. No. WO98/38775 PCT Pub. Date Sep. 3, 1998A modulator and modulation method for orthogonally modulating digital baseband signals include interpolation filters that frequency convert the frequencies of an in-phase component and a quadrature phase component of a digital baseband signal to four times the frequency of an intermediate frequency. DELTA SIGMA modulation circuits are provided and DELTA SIGMA modulate the frequency converted signals. A low pass filter is provided to remove unnecessary components from the DELTA SIGMA modulated signals. A switching circuit selects a signal that has passed through the low pass filter according to an order of an in-phase component, a code inverted component of a quadrature phase component, a code inverted component of the in-phase component and the quadrature phase component, and outputs these signals as a digital orthogonal signal. An N bit D/A converter converts the digital orthogonal signals into analog orthogonal signals.