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 high-speed selectors and DACs. Therefore, the requirement for high-speed 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.