Patent ID: 7616702

Claim:
A transmission circuit for controlling an output power of a transmission signal based on transmission power information, comprising: a modulated signal generating section for modulating input data using a predetermined modulation method to generate a modulated signal; a modulation method changing section for changing a modulation method of the modulated signal generating section; at least one output adjusting section for adjusting an output of the modulated signal; a plurality of amplification sections for amplifying the modulated signal input via the output adjusting section; at least one switching section for switching an amplification section to be operated of the plurality of amplification sections; a switching control section for controlling the switching operation of the switching section based on the transmission power information; an output terminal for outputting the modulated signal amplified by the amplification section as the transmission signal; a level detecting section for detecting a level of the transmission signal; a smoothing circuit for smoothing the level of the transmission signal detected by the level detecting section; and an output adjustment control section for controlling the output adjusting section based on the smoothed level of the transmission signal to adjust the output of the modulated signal, wherein the switching control section controls the modulation method changing section to change the modulation method of the modulated signal generating section to a modulation method having a dynamic range narrower than that of the predetermined modulation method, before controlling the switching section to switch the plurality of amplification sections, the switching control section controls the modulation method changing section to change the modulation method of the modulated signal generating section back to the predetermined modulation method after the switching of the plurality of amplification sections is completed, and the output adjustment control section controls the output adjusting section so that a difference in level between the transmission signal which is smoothed by the smoothing circuit and is before the amplification sections are switched, and the transmission signal which is after the amplification sections are switched, is caused to be smaller than a predetermined difference threshold value, when the modulated signal generating section operates in the modulation method having the narrow dynamic range.