Patent ID: 7406301

Claim:
A modulation-demodulation apparatus comprising: a transmitting circuit including a modulator for modulating a transmission signal; a transmission local oscillator for use with said transmitting circuit; a first frequency divider; connected to the transmission local oscillator and to the modulator, for converting an oscillation frequency of said transmission local oscillator to provide a transmission frequency to the modulator; a receiving circuit including a demodulator for demodulating a reception signal; a reception local oscillator for use with said receiving circuit; and a second frequency divider, connected to the reception local oscillator and to the demodulator, for converting an oscillation frequency of said reception local oscillator to provide a reception frequency to the demodulator, wherein a frequency-dividing ratio of said first frequency divider and a frequency-dividing ratio of said second frequency divider are made different from each other, and wherein local oscillation frequencies of said transmission local oscillator and said reception local oscillator are determined based upon said transmission frequency, said reception frequency and said respective frequency-dividing ratios, wherein a signal corresponding to the transmitting frequency band is not generated in the frequency component of the reception signal leaked into the receiving signal when the reception local oscillation signal is leaked into the transmission local oscillation signal, and wherein said receiving circuit is a direct conversion type and said transmitting circuit is a single conversion type.