Digital I/Q imbalance compensation

摘要

In a communications terminal that has an image reject mixing arrangement, a compensation system provides compensation for phase and amplitude imbalances, which are caused by a demodulating local oscillator employed in the communications terminal. The image reject mixing arrangement comprises a radio-frequency (RF) mixing stage including an in-phase and a quadrature phase branch, which is configured to receive a radio frequency signal and down convert the radio frequency signal to in-phase and quadrature phase intermediate frequency (IF) signals. It also includes a phase splitter unit coupled to the radio-frequency (RF) mixing stage and configured to provide an in-phase local oscillator signal and a quadrature phase local oscillator signal to the RF mixing stage. The phase splitter causes an amplitude imbalance signal DELTA and a phase imbalance signal phi to be generated in the in-phase and quadrature phase branch of the RF mixing stage. A phase splitter compensation unit is coupled to the RF mixing stage and is configured to multiply the in-phase and quadrature phase signals provided by the RF mixing stage by a predetermined compensation factor. An intermediate frequency (IF) mixing stage is coupled to the radio-frequency mixing stage via the phase splitter compensation unit. The IF mixing stage is configured to convert the intermediate signals received from the RF mixing stage to base band frequency region.