TRANSMISSION CIRCUIT BY POLAR MODULATION SYSTEM AND COMMUNICATION APPARATUS USING THE SAME

摘要

A transmission circuit for alleviating the frequency characteristics of the group delay and the attenuation amount in a transmission signal band and expanding the dynamic range to a high frequency band is provided. A ladder-type resistance-type attenuator includes switching elements (12-19), 2R resistor elements (20-28) and R resistor elements (29-35). The 2R and R resistor elements (20-28) and (29-35) are respectively connected to variable capacitor elements (CS1-CS8, CP1-CP8) in parallel. The variable attenuator having such a connection structure is connected to an amplitude modulation loop of the transmission circuit. By controlling the capacitance value of the variable capacitor elements (CS1-CS8, CP1-CP8) using the capacitance value control section (36) when the switching elements are ON/OFF switched based on the transmission power control signal, the influence of parasitic capacitances of the variable capacitor elements (CS1-CS8, CP1-CP8) is suppressed and the group delay between the amplitude modulation and the phase modulation is reduced.