Methods and apparatus for image rejection calibration

An apparatus comprising:

• a transmit signal processing path comprising:
• an image rejection circuit to perform image rejection on a baseband signal, the image rejection circuit comprising at least one gain correction element to be controlled based on a gain compensation value and at least one phase correction element to be controlled based on a phase compensation value;
• a modulator coupled to the image rejection circuit to modulate the baseband signal into a modulated baseband signal;
• a first switch to couple the modulated baseband signal to a first digital-to-analog converter (DAC) of an in-phase path, the first DAC to convert the modulated baseband signal to a first analog signal;
• a second switch to couple the modulated baseband signal to a second DAC of a quadrature path, the second DAC to convert the modulated baseband signal to a second analog signal;
• a first complex mixer coupled to the first DAC and the second DAC, the first complex mixer to upconvert the first analog signal to a first radio frequency (RF) signal and to upconvert the second analog signal to a second RF signal;
• and
• a combiner to combine the first RF signal and the second RF signal into a complex RF signal;
• a receive signal processing path comprising:
• a second complex mixer to downconvert the complex RF signal into a first loopback analog signal and a second loopback analog signal;
• a digitizer to convert the first loopback analog signal to a first loopback digital signal and to convert the second loopback analog signal to a second loopback digital signal;
• and
• at least one digital circuit coupled to the digitizer, the at least one digital circuit to generate a digital value based on the first loopback digital signal and the second loopback digital signal;
• and
• a controller coupled to the transmit signal processing path and the receive signal processing path, wherein the controller, during an image rejection calibration routine, is to cause the second switch to disconnect the quadrature path and cause the at least one digital circuit to measure a first plurality of digital values based on the digital value.

A computer-readable storage medium comprising instructions that when executed by at least one processor of a wireless device cause the wireless device to perform a method comprising:

• injecting, into a transmit signal processing path of the wireless device, a tone signal, the transmit signal processing path comprising an image rejection circuit;
• looping back the tone signal, from the transmit signal processing path to a receive signal processing path of the wireless device, and measuring a first plurality of digital values from the looped back tone signal while a quadrature portion of the transmit signal processing path is disconnected;
• looping back the tone signal, from the transmit signal processing path to the receive signal processing path, and measuring a second plurality of digital values from the looped back tone signal while an in-phase portion of the transmit signal processing path is disconnected;
• determining a gain calibration value for the image rejection circuit based at least in part on the first plurality of digital values and the second plurality of digital values;
• determining a phase calibration value for the image rejection circuit;
• and
• storing the gain calibration value and the phase calibration value in a storage of the wireless device.