Patent ID: 8055215

Claim:
A transmission circuit comprising: a signal converting section for converting input signals into an amplitude signal and a phase signal, respectively, and outputting the amplitude signal and the phase signal; an AM variable fc filter for removing a high frequency component from the amplitude signal by using an AM cutoff frequency; an amplifier for outputting an amplitude component signal which is obtained by amplifying the amplitude signal outputted from the AM variable fc filter; a PM variable fc filter for removing a high frequency component from the phase signal by using a PM cutoff frequency; a phase modulator for phase-modulating the phase signal outputted from the PM variable fc filter so as to output a high-frequency phase-modulated signal; a power amplifier for amplifying the high-frequency phase-modulated signal by using the amplitude component signal outputted from the amplifier, and outputting a resultant signal as a transmission signal; wherein the AM variable fc filter is configured to lower the AM cutoff frequency when a power level signal indicating an output power level of the transmission signal is large, and is configured to increase the AM cutoff frequency when the power level signal is small; wherein the PM variable fc filter is configured to lower the PM cutoff frequency when the power level signal indicating the output power level of the transmission signal is large, and is configured to increase the PM cutoff frequency when the power level signal is small.