A phase-interpolation direct digital synthesizer with an adaptive integrator

A phase-interpolation direct digital synthesizer (DDS) with an adaptive int egrator is described in this paper. Unlike a conventional DDS, it does not use ROM or a D/A converter. Therefore, less power is dissipated and the max imum speed is increased. The delay time for phase interpolation is generate d by the adaptive integrator, which is composed of a capacitance switch arr ay and current switch array, and by a comparator with constant threshold vo ltage. The DDS was fabricated on 0.5-mu m CMOS process technology. The spur ious level is lower than -50 dBc and the power dissipation is 60 mW at a cl ock frequency of 40 MHz and output frequency of about 19 MHz.