US Patent 7747230 Transmission modulation apparatus

A transmission modulation apparatus capable of dealing with characteristic variations of a high-frequency power amplifier without always forming an amplitude loop. Transmission modulation apparatus 100 is configured with level detector 140 that receives input of a level detection control signal and detects the output signal of high-frequency power amplifier 130, and offset voltage correcting section 150 that corrects an offset voltage using collinear approximation including a first point where the relationship between the power supply voltage value and the output voltage starts to shift from linear to non-linear based on an output signal of level detector 140 and a second point where output voltage is a minimum. Offset voltage correction is adaptively executed, and linearity between the voltage value of the baseband amplitude signal and the output voltage of high-frequency power amplifier 130 when the voltage value of the baseband amplitude signal is low is compensated.