Patent ID: 8890634

Claim:
An apparatus comprising: a modulator to generate a baseband digital signal from an information-bearing digital signal, the baseband signal having a time-varying phase and an amplitude defined by a sequence of complex data words, each complex data word having an in-phase (I) data word and a quadrature (Q) data word; a noise-shaping modulator to generate a noise-shaped digital signal from the baseband digital signal such that quantization noise is attenuated by a spectral null of a noise transfer function characterizing the noise-shaping modulator, the spectral null being selected by a noise-shaping parameter corresponding to a selected one of a plurality of output frequencies; and a signal converter to generate an analog signal conveying the information of the information-bearing digital signal on an analog carrier signal having the selected output frequency, wherein the noise-shaping modulator comprises: a quantizer to generate a quantized digital word and a quantization error word for each I data word and for each Q data word of the baseband digital signal; a variable multiplier to multiply the quantization error word of the I data word and the Q data word by a value selected in accordance with the noise-shaping parameter such that quantization noise generated by the quantization of the quantizer is attenuated by the spectral null of the noise transfer function characterizing the noise-shaping modulator; and an adder to add the multiplied quantization error word of the I data word and the Q data word to a corresponding subsequent I data word and Q data word of the baseband digital signal, wherein the quantizer comprises: a multi-conductor bus of conductors by which a number of upper bits of the I data word and the Q data word of the modulated digital signal are directed in respective circuit paths out of the noise-shaping modulator as the noise-shaped digital signal, and a number of lower bits of the I data word and the Q data word of the modulated digital signal are directed to the variable multiplier of the noise-shaping modulator as the quantization error word of the I data word and the Q data word, wherein the noise-shaping modulator comprises an I sigma-delta modulator for the I data word and a Q sigma-delta modulator for the Q data word, the apparatus further comprising a frequency zero selection unit to generate the noise-shaping parameter in accordance with the selected output frequency.