Calibrating amplitude and phase imbalance and DC offset of an analog I/Q modulator in a high-frequency transmitter

A method of calibrating an analog I/Q modulator in a high-frequency transmitter, in which an input signal is weighted in an in-phase path and in a quadrature phase path by respectively a first and a second compensation coefficient prior to the I/Q modulation, and an output signal is produced, comprising:

• in a first method step, providing the high-frequency transmitter
• in a second method step, the first compensation coefficients CI, CQ (3), which affect the sideband suppression of the output signal, and the second compensation coefficients DI, DQ (3), which affect the carrier suppression of the output signal (12), are in each case set to a first predefined value CI,1, CQ,1, DI,1 and DQ,1, in that the input of the I/Q modulator (1) is supplied with an input signal which satisfies a rotating exponential function with the frequency f0, a first I/Q modulator output signal (12) is produced and fed to a first evaluation and the result of the first evaluation is stored, in that,
• in a third method step, the first and second compensation coefficients (3) are in each case set to a second defined value CI,2, DI,2 and DQ,2 and a second I/Q modulator output signal (12) is produced, fed to a second evaluation and the result of the second evaluation is stored, in that,
• in a fourth method step, the first and second compensation coefficients (3) are in each case set to a third defined value CI,3, DI,3 and DQ,3 and a third I/Q modulator output signal (12) is produced, fed to a third evaluation and the result of the third evaluation is stored, in that,
• in a fifth method step, improved compensation coefficients (3) which reduce at least one of an amplitude, a phase imbalance of the I/Q modulator (1) and an amplitude of the residual carrier are calculated for the first and second compensation coefficients (3) from the results stored in the second, third and fourth method steps, and
• wherein the second, third, fourth and fifth method steps are repeated using these improved compensation coefficients (3) until at least one of the error of the amplitude and a phase response of the I/Q modulator (1) lies below a defined threshold value or a defined number of run-throughs of the method is reached.