Nonlinearity calibration scheme for a frequency modulation transmitter

A frequency modulation transmitter comprising:

• a frequency synthesizer for generating a frequency modulated signal of a digitally encoded audio signal, wherein the frequency synthesizer further comprises a digitally controlled oscillator having a variable capacitor array that receives a calibrated fine code for tuning the variable capacitor array to generate the frequency modulated signal with a modulation frequency;
• a nonlinearity estimator for generating an approximation of an integral nonlinearity associated with processing of a fine code for tuning the variable capacitor array to the modulation frequency;
• and
• a subtractor for subtracting the fine code with the approximation of the integral nonlinearity to generate the calibrated fine code.

A method for compensating an integral nonlinearity of a digitally controlled oscillator in a direct modulation type frequency modulation transmitter, comprising:

• receiving a fine code for tuning a variable capacitor array of a digitally controlled oscillator of a direct modulation frequency modulation transmitter to generate a frequency modulated transmit signal of a digitally encoded audio signal;
• determining an integral nonlinearity associated with processing of the fine code using the variable capacitor array;
• generating a calibrated fine code based on the integral nonlinearity;
• and
• forwarding the calibrated fine code to the variable capacitor array to generate the frequency modulated transmit signal.