Direct digital frequency synthesizer using sigma-delta techniques

A modulator for modulating a carrier signal with a baseband signal, comprising:

• means for receiving a stream of complex data values that represent the baseband signal;
• means for generating a sequence of n-bit phase signals representing phase of the carrier signal, wherein n is an integer greater than zero, and each n-bit phase signal comprises a phase estimate signal and a phase error signal, the phase estimate signal comprising a most-significant m bits of the n-bit quantity, wherein m is an integer greater than zero and less than n, and the phase-error signal comprising a least-significant n-m bits of the n-bit quantity;
• a sigma-delta modulator for generating a compensation signal from the phase error signals, wherein the sigma-delta modulator performs at least second order sigma-delta modulation of the phase error signals;
• means for adding the phase estimate signal to the compensation signal and producing therefrom a compensated phase signal;
• means, coupled to the adding means, for providing a carrier signal sample in correspondence with the compensated phase signal;
• and
• means for performing a complex multiplication between the carrier signal sample and one of the baseband signal complex data values, and generating therefrom a modulated carrier signal sample.

A method for generating a waveform, comprising the steps of:

• generating a sequence of n-bit phase signals representing phase of the waveform, wherein n is an integer greater than zero, and each n-bit phase signal comprises a phase estimate signal and a phase error signal, the phase estimate signal comprising a most-significant m bits of the n-bit quantity, wherein m is an integer greater than zero and less than n, and the phase-error signal comprising a least-significant n-m bits of the n-bit quantity;
• using sigma-delta modulation to generate a compensation signal from the phase error signals, wherein the sigma-delta modulation is at least second order sigma-delta modulation;
• adding the phase estimate signal to the compensation signal and producing therefrom a compensated phase signal;
• and
• using the compensated phase signal to generate a waveform sample.

A method for modulating a carrier signal with a baseband signal, comprising the steps of:

• receiving a stream of complex data values that represent the baseband signal;
• generating a sequence of n-bit phase signals representing phase of the carrier signal, wherein n is an integer greater than zero, and each n-bit phase signal comprises a phase estimate signal and a phase error signal, the phase estimate signal comprising a most-significant m bits of the n-bit quantity, wherein m is an integer greater than zero and less than n, and the phase-error signal comprising a least-significant n-m bits of the n-bit quantity;
• using sigma-delta modulation to generate a compensation signal from the phase error signals, wherein the sigma-delta modulation is at least second order sigma-delta modulation;
• adding the phase estimate signal to the compensation signal and producing therefrom a compensated phase signal;
• using the compensated phase signal to generate a carrier signal sample;
• and
• performing a complex multiplication between the carrier signal sample and one of the baseband signal complex data values, and generating therefrom a modulated carrier signal sample.