Method and system for calibrating quadrature modulators

A calibration method for reducing modulation errors in a telecommunication transmitter apparatus, the calibration method including the steps of:

• providing a pair of test signals, the test signals being substantially in quadrature to each other;
• iterating an estimation loop including:
• generating a modulated signal by modulating the test signals, the modulation introducing a modulation error;
• obtaining a squared signal corresponding to the square of the modulated signal;
• calculating a transformed signal corresponding to the squared signal in the frequency domain;
• calculating an error indicator according to the modulus of the transformed signal, the error indicator being indicative of the modulation error;
• calculating a compensation, to be applied to the test signals for counterbalancing the modulation error, according to the error indicator, and
• applying said compensation to the test signals,
• until the error indicator reaches a threshold, and
• storing an indication of the compensation resulting from a last iteration of the estimation loop for the application of the compensation to each pair of operative signals managed by the telecommunication transmitter apparatus during operation thereof, wherein the modulation error includes a phase error and a gain error, the step of calculating the compensation including:
• calculating a phase compensation to be applied to the test signals for counterbalancing the phase error and a gain compensation to be applied to the test signals for counterbalancing the gain error.

A computer program product including a computer-usable medium embodying a computer program, the computer program when executed on a calibration system causing the system to perform a calibration method for reducing modulation errors in a telecommunication transmitter apparatus, wherein the method includes the steps of:

• providing a pair of test signals, the test signals being substantially in quadrature to each other;
• iterating an estimation loop including:
• generating a modulated signal by modulating the test signals, the modulation introducing a modulation error;
• obtaining a squared signal corresponding to the square of the modulated signal;
• calculating a transformed signal corresponding to the squared signal in the frequency domain;
• calculating an error indicator according to the modulus of the transformed signal, the error indicator being indicative of the modulation error;
• calculating a compensation, to be applied to the test signals for counterbalancing the modulation error, according to the error indicator, and
• applying said compensation to the test signals,
• until the error indicator reaches a threshold, and
• storing an indication of the compensation resulting from a last iteration of the estimation loop for the application of the compensation to each pair of operative signals managed by the telecommunication transmitter apparatus during operation thereof.

A calibration system for reducing modulation errors in a telecommunication transmitter apparatus, the calibration system including:

• means for providing a pair of test signals, the test signals being substantially in quadrature to each other;
• means for generating a modulated signal by modulating the test signals, the modulation introducing a modulation error;
• means for obtaining a squared signal corresponding to the square of the modulated signal;
• means for calculating a transformed signal corresponding to the squared signal in the frequency domain;
• means for calculating an error indicator corresponding to the modulus of the transformed signal, the error indicator being indicative of the modulation error;
• means for calculating a compensation, to be applied to the test signals for counterbalancing the modulation error, according to the error indicator,
• means for applying said compensation to the test signals, and
• means for storing an indication of the compensation for the application of the compensation to each pair of operative signals managed by the telecommunication transmitter apparatus during operation thereof.

A calibration system for reducing modulation errors in a telecommunication transmitter apparatus, the calibration system including:

• a test generator for generating a pair of test signals, the test signal being substantially in quadrature to each other;
• a modulator for generating a modulated signal by modulating the test signals, the modulation introducing a modulation error;
• a non-linear quadratic block for obtaining a squared signal corresponding to the square of the modulated signal;
• an estimator for calculating:
• a transformed signal corresponding to the squared signal in the frequency domain,
• an error indicator corresponding to the modulus of the transformed signal, the error indicator being indicative of the modulation error, and
• a compensation, to be applied to the test signals for counterbalancing the modulation error, according to the error indication;
• a compensator for applying said compensation to the test signals, and
• a memory for storing an indication of the compensation for the application of the compensation to each pair of operative signals managed by the telecommunication transmitter apparatus during operation thereof.

A transmitter apparatus including a calibration system for reducing modulation errors, the calibration system including:

• means for providing a pair of test signals, the test signals being substantially in quadrature to each other;
• means for generating a modulated signal by modulating the test signals, the modulation introducing a modulation error;
• means for obtaining a squared signal corresponding to the square of the modulated signal;
• means for calculating a transformed signal corresponding to the squared signal in the frequency domain;
• means for calculating an error indicator corresponding to the modulus of the transformed signal, the error indicator being indicative of the modulation error;
• means for calculating a compensation, to be applied to the test signals for counterbalancing the modulation error, according to the error indicator,
• means for applying said compensation to the test signals, and
• means for storing an indication of the compensation for the application of the compensation to each pair of two operative signals managed by the telecommunication transmitter apparatus during operation thereof.

A transmitter apparatus including a calibration system for reducing modulation errors, the calibration system including:

• a test generator for generating a pair of test signals, the test signal being substantially in quadrature to each other;
• a modulator for generating a modulated signal by modulating the test signals, the modulation introducing a modulation error;
• a non-linear quadratic block for obtaining a squared signal corresponding to the square of the modulated signal;
• an estimator for calculating:
• a transformed signal corresponding to the squared signal in the frequency domain,
• an error indicator corresponding to the modulus of the transformed signal, the error indicator being indicative of the modulation error, and
• a compensation, to be applied to the test signals for counterbalancing the modulation error, according to the error indication;
• a compensator for applying said compensation to the test signals, and
• a memory for storing an indication of the compensation for the application of the compensation to each pair of operative signals managed by the telecommunication transmitter apparatus during operation thereof.