Patent ID: 8442153

Claim:
A transmission circuit that amplifies a power of an input transmission signal by switching an operation mode of the transmission circuit between a polar modulation mode and a quadrature modulation mode, the transmission circuit comprising: a radio frequency integrated circuit that controls the operation mode of the transmission circuit on the basis of the input transmission signal, generates an amplitude-modulated signal and a phase-modulated signal in the polar modulation mode, and generates a quadrature-modulated signal in the quadrature modulation mode; an envelope management integrated circuit that generates a control voltage on the basis of the amplitude-modulated signal from the radio frequency integrated circuit or a power supply voltage; and a power amplifier that amplifies a power of the phase-modulated signal or the quadrature-modulated signal from the radio frequency integrated circuit on the basis of the control voltage from the envelope management integrated circuit, the envelope management integrated circuit including: a DC-DC converter that outputs the power supply voltage for the polar modulation mode or the quadrature modulation mode on the basis of the control of the operation mode by the radio frequency integrated circuit; a transistor whose source is connected to an output of the DC-DC converter and whose drain is connected to a power supply terminal of the power amplifier; a regulator having an input terminal to which the amplitude-modulated signal from the radio frequency integrated circuit is input, and a common terminal which is connected to the drain of the transistor and to which the power supply voltage for the polar modulation mode or the quadrature modulation mode from the DC-DC converter is input; and a regulator output selector switch that, on the basis of the control of the operation mode by the radio frequency integrated circuit, connects a gate of the transistor to an output terminal of the regulator while the operation mode of the transmission circuit is the polar modulation mode, and, when the operation mode of the transmission circuit has switched from the polar modulation mode to the quadrature modulation mode, switches a connection destination of the gate of the transistor to a fixed potential after an elapse of a predetermined time until the power supply voltage for the quadrature modulation mode output from the DC-DC converter stabilizes at a desired value.