In wireless communications devices using radio waves, it is necessary for the device to comply with communication standards in order to efficiently utilize radio waves while preventing interference with the other devices. For example, in mobile phones, it is necessary for the mobile phone to control its transmission power at a specified value, using a power detector that detects transmission power.
In order to accurately detect transmission power for diversified communication standards, it is demanded to provide a wide detectable power range (dynamic range). Moreover, in order to accurately detect transmission power for highly sophisticated, diversified modulation modes, a root-mean-square detector formed of bipolar transistors or the like is used.