Digital I/Q imbalance compensation

In a communications terminal having an image reject mixing arrangement a compensation system for providing compensation for phase and amplitude imbalances caused by a demodulating local oscillator employed in the communications terminal, said compensation system comprising:

• a radio-frequency (RF) mixing stage including an in-phase and a quadrature phase branch, configured to receive a radio frequency signal and down convert said radio frequency signal to in-phase and quadrature phase intermediate frequency (IF) signals;
• a phase splitter unit coupled to said radio-frequency (RF) mixing stage and configured to provide an in-phase local oscillator signal and a quadrature phase local oscillator signal to said RF mixing stage, said phase splitter causing an amplitude imbalance signal Δ and a phase imbalance signal φ to be generated in said in-phase and quadrature phase branch of said RF mixing stage;
• a processing circuit coupled to said RF mixing stage and configured to measure a first value associated with said amplitude imbalance and a second value associated with said phase imbalance;
• a phase splitter compensation unit coupled to said RF mixing stage and configured to multiply said in-phase and quadrature phase signals provided by said RF mixing stage by a predetermined compensation factor associated with said measured first and second values:
• an intermediate frequency (IF) mixing stage coupled to said radio-frequency mixing stage via said phase splitter compensation unit, said IF mixing stage configured to convert said intermediate signals received from said RF mixing stage to base band frequency region;
• and
• a transmitter stage coupled to said RF mixing stage and configured to provide a test tone signal to said RF mixing stage.

In a communications terminal employing an image-rejection system a method for compensating image signals caused by local oscillator of said communications terminal comprising the steps of:

• receiving a radio frequency signal and down converting said radio frequency signal in a radio-frequency (RF) mixing stage so as to provide in-phase and quadrature phase intermediate frequency (IF) signals;
• providing an in-phase local oscillator signal and a quadrature phase local oscillator signal to said RF mixing stage via a phase splitter that causes said image signals that are compensated, said phase splitter causing an amplitude imbalance signal Δ and a phase imbalance signal φ;
• measuring, via a processing circuit coupled to said RF mixing stage, a first value associated with said amplitude imbalance and a second value associated with said phase imbalance;
• multiplying said in-phase and quadrature phase signals provided by said RF mixing stage by a predetermined compensation factor associated with said measured first and second values;
• and
• converting said intermediate signals received from said RF mixing stage to base band frequency region via an intermediate frequency (IF) mixing stage coupled to said radio-frequency mixing stage.