A gain/phase mismatch calibration procedure for RF I/Q downconverters

We propose a calibration procedure to compensate for gain and phase mismatch errors in RF I/Q downconversion stages requiring neither external reference signals nor adaptive techniques. The proposed indirect compensation technique is based on the use of the local oscillator (LO) signal as the reference for error measurements. A number of mismatch parameters are first estimated by an algorithm running in the DSP after the analog-to-digital (A/D) converter and then used to correct the downconverted signal digitally during normal operation. A test circuit has been designed in 0.13 μm CMOS technology and it is under fabrication. Circuit simulations exhibit an image-rejection ratio, IRR, of about 60 dB for a LO 1% amplitude and 3° phase mismatch.