Apparatus, and a related method, for converting digital signals directly
to radio-frequency (RF) analog signals. The apparatus includes a single
high-speed delta-sigma modulator and an integrated upsampler that
increases the data rate of digital input samples by a selected factor,
such as nine times. The delta-sigma modulator is configured to include a
feedback multiplier coefficients that are selected to greatly facilitate
operation of associated adders. At least one critical adder includes a
carry-select adder modification that further speeds up the add operation
and ensures that the apparatus operates at desirably high frequencies.