Quadrature demodulator and method for quadrature demodulation

A quadrature demodulator, comprising:

• a first A/D converter for digitizing in-phase components of a quadrature modulation signal;
• a second A/D converter for digitizing quadrature components of the quadrature modulation signal;
• a complex multiplier for complex multiplying the outputs from the first and the second A/D converters with a cosine wave component and a sine wave component to produce demodulated in-phase and quadrature components;
• a phase detector for detecting a phase angle of a residual carrier in the demodulated signal based on the constellation symbols of the demodulated in-phase and quadrature components;
• an error detector for detecting the error components of the phase angle of the output of the phase detector;
• a low pass filter for smoothing the error output received from the error detector;
• a first numerical control oscillator for generating a local main-carrier in accordance with the error signal output of the low pass filter;
• a cosine converter for converting the local main-carrier output from the first numerical control oscillator into a cosine wave component;
• a sine converter for converting the local main-carrier output from the first numerical control oscillator into a sine wave component;
• a second numerical control oscillator for generating a local sub-carrier in accordance with the output of the low pass filter;
• a first gate for allowing or blocking the transmission of the output signal supplied from the low pass filter to the first numerical control oscillator;
• and
• a second gate for allowing or blocking the transmission of the output signal supplied from the low pass filter to the error detector to the second numerical control oscillator.

A method for demodulating quadrature modulation signal, comprising the steps of:

• receiving a quadrature modulated signal;
• generating a local carrier;
• demodulating a quadrature modulation signal by complex-multiplying the quadrature modulated signal with the local carrier generated in the local oscillator;
• detecting a symbol error between the carrier of the modulated signal and the local carrier from the signal demodulated at the complex-multiplier;
• feeding back to control the local carrier generated at the local oscillator by feeding back the symbol error detected at the symbol error detector to the local oscillator;
• generating a recovered phase signal under the control of the symbol error branched from the feedback loop;
• and
• compensating the local carrier to reduce the symbol error according to the recovered phase signal.

A method for demodulating quadrature modulation signal, comprising the steps of:

• digitizing the incoming in-phase components;
• digitizing the incoming quadrature component;
• complex multiplying the digitized in-phase and quadrature components with a cosine wave component and a sine wave component to demodulate baseband in-phase and quadrature components;
• detecting the phase angle from the constellation symbols of the demodulated in-phase and quadrature components in the phase detector;
• detecting the error based upon the phase angle;
• adjusting the gain of the error of the phase angle by a predetermined level;
• smoothing out the gain of the error;
• generating a local main-carrier at the first numerical control oscillator in accordance with the output of the smoothed signal;
• converting the phase angle outputted from the first numerical control oscillator to the cosine wave component;
• converting the phase angle outputted from the first numerical control oscillator to the sine wave component;
• oscillating the frequency in the second numerical control oscillator based upon the output of the smoothed signal;
• allowing or blocking the transmission of the smoothed signal to the first numerical control oscillator;
• and
• allowing or blocking the transmission of the oscillation signal of the second numerical control oscillator to the differentiator.