Patent ID: 6744825
Filing Date: 2004-06-01
Classification: H03M,H04L

Abstract:
A method of quadrature modulation and digital-to-analog conversion, comprising the steps of:sampling a digitally represented input complex baseband signal, represented by an in-phase (I) component and a quadrature-phase (Q) component, at a sampling rate to achieve a desired noise shaping; separately quantizing the in-phase component and the quadrature-phase component to a number of bits per sample to produce quantized versions of the in-phase and quadrature-phase components, the quantizing step introducing quantization noise that is shaped spectrally to have energy falling largely outside the frequency band of the input complex baseband signal; quadrature modulating the quantized versions of the in-phase and quadrature-phase components to a quadrature modulated signal at a carrier frequency equal to a quadrature modulated signal exactly one quarter of a sampling rate fs to obtain a quadrature modulated signal with repeated spectra of the modulated signal being found around all odd multiples of the carrier frequency; converting the quadrature modulated signal to an analog form signal through a digital-to-analog converter; and eliminating unwanted energy outside a frequency band used for a target channel by passing the analog form signal through a bandpass filter wherein, said quantizing step uses sigma-delta quantization, and subsequent to said quantizing step and prior to the quadrature modulating step, there is a further step of separately rate-converting the quantized versions of the in-phase and quadrature-phase components by a factor {fraction (1/2)}M, where M is a selected positive integer, to a sampling rate fs=2fc/(2kâˆ’1) by repetition of each quantized sample a total of {fraction (1/2)}M times if M is an even number greater than 2, by no rate-conversion if M=2, and by omission of an in-phase component sample at every second point of time and omission of a quadrature-phase component at all points of time other than every second point of time if M=1, where k is a selected positive integer and fc is the carrier frequency to which the input complex baseband signal is to be modulated.