Sideband suppression method and apparatus for quadrature modulator using magnitude measurements

A method for correcting a gain imbalance and a phase imbalance in a quadrature modulator, comprising:

• applying a first voltage level to a first quadrature modulator channel and measuring a first output amplitude;
• applying a second voltage level to a second quadrature modulator channel and measuring a second output amplitude;
• determining a gain correction factor as a function of the first output amplitude and the second output amplitude;
• correcting the gain imbalance using said gain correction factor;
• applying a first phase and a third voltage level to the first quadrature modulator channel while applying the third voltage level to the second quadrature modulator channel and measuring a third output amplitude;
• applying the first phase and the third voltage level to the first quadrature modulator channel while applying a fourth voltage level to the second quadrature modulator channel and measuring a fourth output amplitude;
• applying a second phase and the third voltage level to the first quadrature modulator channel while applying the third voltage level to the second quadrature modulator channel and measuring a fifth output amplitude;
• applying the second phase and the third voltage level to the first quadrature modulator channel while applying the fourth voltage level to the second quadrature modulator channel and measuring a sixth output amplitude;
• determining a phase correction factor as a function of the third, fourth, fifth and sixth output amplitudes and the first phase;
• and
• correcting the phase imbalance using said phase correction factor.

A baseband correction unit for correcting a gain and a phase imbalance in a quadrature modulator, comprising:

• an error estimation circuit coupled to an output of the quadrature modulator via a detection circuit and to a pair of inputs to the quadrature modulator via a gain and phase compensating circuit, the error estimation circuit being operable to:
• apply at least one predetermined voltage at a predetermined phase to the pair of inputs to the quadrature modulator and to detect at least one amplitude of an output voltage of said quadrature modulator;
• calculate a gain and a phase imbalance as a function of said at least one detected amplitude, and to apply a gain and a phase correction to the pair of inputs to the quadrature modulator;
• the error estimation circuit comprising:
• a sideband suppression look-up table and control circuit coupled to the detection circuit, the sideband suppression look-up table being operable to map a detected magnitude to a phase offset;
• and
• a complex phase rotator coupled to the sideband suppression look-up table and control circuit and to the pair of inputs to the quadrature modulator, the complex phase rotator being operable to apply the phase offset to the pair of inputs to the quadrature modulator.

A baseband correction unit for correcting a phase imbalance in a quadrature modulator, comprising:

• an error estimation circuit coupled to the quadrature modulator for applying a voltage to the quadrature modulator, the error estimation circuit comprising:
• a sideband suppression look-up table and control circuit, the sideband suppression look-up table being operable to map a detected magnitude to a phase offset;
• and
• a complex phase rotator coupled to the sideband suppression look-up table and control circuit and to the quadrature modulator, the complex phase rotator being operable to apply the phase offset to the quadrature modulator.