A 3-V programmable clock generator with a built-in phase interpolator

A fully digital DDS type clock generator with good frequency resolution and sub-ns phase jitter is described. Its operation is based on a time-to-digital converter that is used to interpolate the zero crossing time inside the system clock cycle. A prototype circuit with 24 bit NCO and 32 tap phase interpolator has been designed for 2.8 V power supply and 40 MHz clock frequency, which results in 225 ps(rms) and 780 ps(p-p) phase jitter 40 dBc spurious-free dynamic range, and tuning range from 0 up to the 40 MHz clock frequency. The prototype is not functioning completely but it proves the concept.