A ROM-Less DDS with High-Speed Selectors for Reduction in DAC Settling Time Requirements

This paper presents a new phase interpolation direct digital synthesizer (DDS) for reduction in digital-to-analog converter (DAC) performance requirements. The phase interpolator makes the accumulator overflow pulses line up at exactly equal intervals, so the DDS can output a square wave with high frequency purity. The newly proposed two-step integrator generates two-step ramp waves by combining highspeed selectors and DACs. Therefore, the requirement for highspeed settling time for the DAC, which was required in the conventional phase interpolation type DDS, is relaxed. As a result, the proposed DDS can achieve low power consumption, high-speed operation, and improved output frequency purity. The measured spurious free dynamic range of prototype DDS output is 53.7 dBc.