A METHOD AND SYSTEM FOR QUADRATURE MODULATION AND DIGITAL-TO-ANALOG CONVERSION

摘要

A method and system for quadrature modulation and digital-to-analog conversion of a sampled and digitally represented complex baseband signal which permits the use of simple, power-saving, accurate and effective digital signal processing up to a very high intermediate frequency. The invention requires an input signal in the form of an oversampled complex baseband signal. The in-phase (I) and quadrature-phase (Q) components of this signal are first quantized to preferably 1 bit per sample, e.g., with the aid of SIGMA DELTA modulation, so that the quantization noise is essentially forced outside the frequency band of the working signal. Then the smapling rate of the quantized versions of I and Q is converted to four times the desired carrier frequency, before the signal is quadrature modulated with a signal frequency exactly equal to one quarter of the final sampling rate. Finally the ready processed digital signal is converted to an analog quadrature modulated signal through a digital-to-analog converter followed by a bandpass filter.