Study About The Method Of Improving Sampling Rate Of Arbitrary Waveform Generator

Signal source is widely used in the field of electronic measurements, such as voltage source, multimeter and oscilloscope, etc. Arbitrary waveform generator based on direct digital synthesis technology has been largely replacing the traditional signal source, because of its high frequency resolution, high frequency stability, fast frequency switching, and continuous output phase when switching, etc. As the test system is gradually more complicated, higher requirements for signal source have been put forward, such as, a higher output frequency, more kinds of waveform and channels, and other special indexes. So it is of great significance to studies how to improve the sampling rate of arbitrary waveform generator effectively, on the premise of reducing the cost.Focusing on how to improve the sampling rate of arbitrary waveform synthesis, this paper introduces the split-phase storage, interpolation and pseudo interpolation methods, and makes a comparison of their own strengths and weaknesses. Combined with the actual project application, this paper uses the split-phase storage technology to solve the limit of the phase accumulator and waveform memory speed in the DDS system. The sampling rate of arbitrary waveform synthesis has been improved effectively, and the 500MSa/s waveform synthesis design is realized finally.At first, this paper introduces the working principle of DDS technology, analyzes the advantages and disadvantages of using a dedicated DDS chip and FPGA implement waveform synthesis, and choose the FPGA implement waveform synthesis program with great flexibility and portaility.Then it gives the basic structure of DDS technology based on the split-phase storage, and the DDS firmware logic module inside the FPGA which is designed by programming. The DDS firmware logic module mainly includes address assignments and decoding module, high-speed phase accumulator, precisely adjustable dual-channel phase difference module and parallel-serial conversion module, etc. According to the indexes of system, this paper designs the system hardware circuits which mainly includes the external clock module, FPGA module, DAC module, channel output module and power module. The system is a high-speed digital-analog mixing system, so it designs the high-speed PCB according to the circuit principle diagram, and researches the signal integrity of the circuit board. Several methods are conduted, such as standard layout and route, reasonable PCB, controllable transmission lines and reduce the system noise to make the system work more stably.Finally, this paper tests the circuit board which has been debug completely. The test results are as follows:the system sampling rate is 500MSa/s, maximum output frequency is 160MHz, the output signal amplitude range 4mVpp to 20Vpp. Besides the circuit board can output various kinds of conventional waveform, modulation waveform and arbitrary waveform. Test results prove that the DDS technology based on the split-phase storage can improve the sampling rate of arbitrary waveform synthesis effectively.