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

A method for measuring imperfections in the operation of a digital quadrature demodulator when an output signal of a quadrature mixer of the demodulator comprises quadrature-phase I and Q channels, whereby during a normal operation of the demodulator from the output signal of the quadrature mixer of the demodulator is determined offset voltages, an imbalance in the amplitudes of the I and Q channels, a quadrature error between the I and Q channels and a total amplitude error, characterized in that the method comprises steps in which

• from the amplitude of the output signal of the demodulator quadrature mixer, i.e. from the amplitude of a vector formed by the I and Q channels, are taken numerous momentary samples at a rate based on a symbol clock of the demodulator;
• a direction angle of the demodulator output signal vector corresponding to the samples is divided, on the basis of the voltages of the I and Q channels, into different direction angle sectors;
• and
• from the amplitude sample deviations between the different direction angle sectors or from a nominal value are calculated the magnitudes of the distortions in the demodulator operation.

A digital quadrature modulator comprising means (11) for modulating quadrature-phase I and Q input signals to generate an output signal comprising quadrature-phase I and Q components, characterized in that the modulator further comprises

• means (12) for taking momentary amplitude samples from the output signal of the modulator (11), at a rate based on a symbol clock (SCLK) of the modulator;
• means (13) for classifying a symbol to be modulated at a particular time into a particular direction angle sector;
• means (13) for linking the amplitude samples of the output signal to the direction angle sector corresponding to the symbol to be transmitted at a particular time;
• and
• means (13) for comparing the amplitudes of the samples belonging to a particular direction angle sector with other direction angle sectors or with an ideal value, for determining from the output signal of the modulator a local oscillator carrier wave leak, an amplitude imbalance between I and Q channels, a quadrature error between the I and Q channels and an amplitude error.

A digital quadrature demodulator comprising a quadrature mixer (21) for generating analog quadrature-phase I and Q output signals from a quadrature modulated input signal, characterized in that the demodulator comprises

• means (22) for taking momentary samples from the I and Q output signals of the quadrature mixer (21) at a rate based on a symbol clock (MCLK) of the demodulator;
• means (22) for calculating total amplitude samples of the output signal from I and Q samples;
• means (22) for classifying a direction angle of the symbol received at a particular time into a particular direction angle sector;
• means (23) for linking the amplitude samples of the output signal of the quadrature mixer (21) to a particular direction angle sector;
• and
• means (23) for comparing the amplitudes of the samples belonging to a particular direction angle sector with an ideal value or with other sectors, for determining from the output signal of the quadrature mixer offset voltages, an amplitude imbalance between I and Q channels, a quadrature error between the I and Q channels and a total amplitude error.