Research Of DDS Signal Generator Based On FPGA

DDS (Direct Digital Synthesizer) is a new theory of direct synthesis waveform from phase concept. In the recent30years,with the development of VLSI(Very Large Scale Integration),FPGA(Field Programmable Gate Array),CPLD(Complex Programmable Logic Device)and the further research of DDS theory, DDS technology has developed rapidly.Based on VHDL,FPGA chip and with the support of D/A converter,filter, high-speed amplitude amplifier and power amplifier, this system not only achieves the generating and switching of sine wave,square wave and triangle wave, but also realizes amplitude controlling, frequency controlling and displaying.This paper firstly introduces the current situation of the development of DDS technology, working principle, spectrum analysis and technical characteristics, and on this basis, proposes the overall plan of DDS signal generator system. The FPGA chip is used to control the4*4keyboard and LCD as a state machine, and to process the input data from the keyboard in order to get the frequency control word, and then through the DDS module such as quadrant mapping module, ROM table to generate sine wave, square wave and triangular wave with it’s internal logic resources, the frequency is determined by the input frequency from the keyboard. This system uses eight bits, high-speed D/A converter to convert digital signals from FPGA chip to analog signals. Spurious signals is filtered by the8-order butterworth passive low-pass filter to get smooth waveform. The amplitude of the output waveform is extended by high-speed amplitude amplifier, this system uses current feedback amplifier to achieve the broadband range magnitude of amplification, Finally through the power amplifier to output waveform.This system completes the hardware circuit and software design, and uses Protel DXP software to design PCB board. This design can achieve the desired requirements through repeatedly debugging, and the result shows that this design of the system is feasible and correct.