| 摘要 |
A transmission circuit alleviates the frequency characteristics of a group delay and an attenuation amount in a transmission signal band and expands a dynamic range to a high frequency band. A ladder-type resistance-type attenuator includes switching elements, 2R resistor elements and R resistor elements. The 2R and R resistor elements are respectively connected to variable capacitor elements 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 using the capacitance value control section 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 is suppressed and the group delay between the amplitude modulation and the phase modulation is reduced.
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