Patent ID: 7504976

Claim:
An apparatus for generating radio-frequency signals directly from digital signals representing the instantaneous amplitude of the desired radio-frequency signals, said apparatus comprising: a sigma-delta encoder coupled to receive said digital signals, for generating sigma-delta encoded digital signals; a tapped digital shift register including an input port coupled to receive said sigma-delta encoded digital signals and also including a plurality of output ports at which delayed digital signals appear; a set of DAC cells, each cell of said set of DAC cells being coupled for receiving one of said delayed digital signals from said tapped digital shift register, for converting the corresponding tapped digital signal into a current, thereby generating a set of currents; a combiner coupled to said set of DAC cells, for combining said set of currents into a combined current representing reconstructed signal, said combiner comprising a first transmission line for receiving said set of currents, and at least a second transmission line having similar phase progression for delaying clock signals applied to said tapped digital shift register; and a set of static digital drivers and a set of digital control sources are coupled to said set of DAC cells, for weighting the individual currents of said set of currents so that said radio frequency signals are reconstructed within a finite passband.