说明：  no intro
(The design is based on a digital frequency synthesis technology, to achieve wave synthesis by sine wave look-up tables. Direct Digital Synthesis Technology (DDS) is an advanced circuit structure, the output signal frequency is controlled precisely and rapidly in all-digital process, DDS technology has been applied in output signal frequency increment. DDS signals generated own high frequency resolution, frequency switching speed and continuous phase when frequency switching, low-output phase noise and can generate arbitrary waveform, and so on. Basic principles of the DDS is introduced in the paper, frequency form and stray inhabitation of the DDS is analyzed. Procedures designed with high-speed hardware description language VHDL describe DDS, and design a sine wave, triangle wave, square-wave signal generator by it.The hardware and software has been designed, prototype and circuit has been tested partly. )