Digital Calibration of I/Q Mismatches

In wireless receivers that employ analog quadrature demodulation, analog quadrature sampling or double quadrature sampling schemes as described in the previous chapter, gain and phase imbalances between I and Q channels always exist. The I/Q mismatch will produce the so-called “self-image” problem, that is, the folding of the positive frequency components of the received signal to the negative frequency range and vice versa. In a receiver which receives only one radio channel signal, the impact of the self-image is the lowering of the signal-to-noise ratio [1]. If I/Q mismatches are not severe, say, amplitude mismatch below 1 dB and phase error below 5°, the self-image is usually tolerable in such a single channel receiver.