Abstract: An improved circuit and technique for obtaining phase-coherent synthesis using a direct digital synthesizer (DDS). In the phase-coherent frequency synthesis device of the invention, a computational engine constructed from a large programmable gate array, a digital signal processing microprocessor, or a number of discrete digital logic blocks generates information sent to the DDS for generating an output frequency, .function..sub.out, which is in phase with all previous outputs of the device at the same frequency.