Patent ID: 8060038
Filing Date: 2011-11-15
Classification: H03F,H04B

Abstract:
1. A radio transmitter using a Cartesian loop comprising: a combiner which combines input I/Q signals to be transmitted with feedback I/Q signals to generate combined I/Q signals; a quadrature modulator which performs quadrature modulation on the combined I/Q signals to generate a quadrature modulated signal; a power amplifier which amplifies the quadrature modulated signal to output a transmission RF signal; a quadrature demodulator which performs quadrature demodulation, by using a local signal, on a feedback RF signal branched from the transmit RF signal to generate the feedback I/Q signals; a detector which detects each amplitude difference and each phase difference between the input I/Q signals and the feedback I/Q signals; a switch to turn on and off input of the feedback I/Q signals to the combiner; a power setting unit which sets transmission power of the transmit RF signal; a control signal generator to generate at least one amplitude control signal which minimizes the amplitude difference and at least one phase control signal which minimizes the phase difference, in a state where the transmission power is set, during for a period during which the switch is turned off; a memory which stores the amplitude control signal and the phase control signal; an amplitude adjuster which adjusts an amplitude of the feedback RF signal in accordance with the amplitude control signal stored in the memory, during for a period during which the switch is turned on; a phase adjuster which adjusts a phase of the local signal in accordance with the phase control signal stored in the memory, during for the period during which the switch is turned on; and a gain setting unit which sets a first loop gain for the Cartesian loop when the switch is turned off, and sets a second loop gain higher than the first loop gain for the Cartesian loop when the switch is changed from an off state to an on state.