Calibrate output matching for correct output power

A calibration unit that separately calibrates real and imaginary parts of a load impedance of an on-chip differential power amplifier, the impedance matching network comprising:

• an adaptive impedance unit comprising:
• an on-chip balun having a first winding operatively connected between differential outputs of the differential power amplifier;
• a first variable impedance element operatively connected to the differential outputs in parallel with the first winding of the balun and configured to control the imaginary part of the load impedance;
• a second variable impedance element operatively connected in parallel with a second winding of the balun and configured to control the real part of the load impedance;
• a controller operatively connected to the adaptive impedance unit and the peak detector, said controller comprising an impedance selector configured to apply a plurality of first and second impedance values to the first and second variable impedance elements, respectively;
• and
• a voltage detector configured to measure an output voltage at the output of the power amplifier for one or more pairs of the first and second impedance values;
• wherein the impedance selector is further configured to calibrate the imaginary and real parts of the load impedance by selecting first and second calibration values from the plurality of first and second impedance values, respectively, based on a comparison between the measured output voltages and a reference voltage.

A method of separately calibrating real and imaginary parts of a load impedance of an on-chip differential power amplifier, the method comprising:

• connecting a first winding of an on-chip balun between differential outputs of the differential power amplifier;
• connecting a first variable impedance element to the differential outputs in parallel with the first winding of the balun;
• connecting a second variable impedance element in parallel with a second winding of the balun;
• calibrating the imaginary and real parts of the load impedance by:
• applying a plurality of first and second impedance values to the first and second variable impedance elements, respectively;
• measuring an output voltage at the output of the power amplifier for one or more pairs of the first and second impedance values;
• and
• selecting first and second calibration values for the first and second impedance elements from the plurality of first and second impedance values, respectively, based on a comparison between the measured output voltages and a reference voltage.