Method in digital quadrature modulator and demodulator, and digital quadrature modulator and demodulator

A digital quadrature demodulator including a quadrature mixer for generating analog quadrature-phase I and Q output signals from a quadrature modulated input signal, the demodulator further comprising:

• means for taking momentary samples from the I and Q output signals of the quadrature mixer at a rate based on a symbol clock of the demodulator;
• means for calculating total amplitude samples of the output signal from I and Q samples as distances from the origin;
• means for classifying a direction angle of the symbol received at a particular time into a particular direction angle sector;
• means for linking the amplitude samples of the output signals of the quadrature mixer to a particular direction angle sector;
• means for comparing the amplitudes of the samples belonging to a particular direction angle sector with an ideal value or with other sectors, to determine, from the output signal of the quadrature mixer offset voltages, operation distortions including at least an amplitude imbalance between I and Q channels, a quadrature error between the I and Q channels and a total amplitude error;
• and
• means for correcting adjusting parameters of the demodulator in response to the operation distortions by generating feedback loops, which correct for all the operation distortions simultaneously in an iterative manner.