Design And Implementation Of The Arbitrary Waveform Generator Hardware System Based On FPGA

Signal generator is one of the general instruments that widely used in modern testing field, which broadly used in electronic circuits, automatic control and scientific experiment, etc. Along with the rapid development of current electronic technology, the kind of device under test is more and more abundant, excitation signal required by test is more and more complicated, so the traditional signal generators can not satisfy the requirements of these tests. The emergence of arbitrary waveform generator provides a new solution for modern electronic measurement. It can not only generate common standard waveforms, but also utilize the microprocessor and waveform editing software to generation arbitrary waveform signals required by system test. Its performance is obviously superior to the traditional signal generator, which can well meet the needs of modern electronic measurement. It represents development direction of the signal source.The rapid development of arbitrary waveform generator in modern electronic measurement field, the key is due to the proposal of direct digital frequency synthesis (DDS) technique. Direct digital frequency synthesis technology is an all-digital frequency synthesis technology proposed in the 1970s, which has such good characteristics:fast frequency conversion, high frequency resolution, low phase noise, variable frequency phase continuous, etc, and provides a good technical means for generating arbitrary waveform through the look-up table. In recent years, with the rapid development of modern electronic technology and VLSI technology, field programmable gates array (FPGA) resource capacity, working frequency and integration have been greatly raised, which provides favorable conditions for the realization of DDS circuit. It has the very good design flexibility through FPGA programming custom DDS circuit required by the system, not only reduces cost, but also improves the performance of arbitrary waveform generator, which is the main content of this research.This paper, based on the basic principle of DDS, systematically elaborated the waveform synthesis theory. This paper focuses on the detailed analysis of DDS output signal spectrum characteristics and spectrum stray through its mathematic comprehensive expression, and also studies the improvement methods of spectrum stray, which lays a solid foundation for DDS hardware circuit designing. After the comparative Analysis of two arbitrary waveform generator design method based on DDS technology, proposed a arbitrary waveform generator's overall design scheme based on double DDS circuit structure as core circuit within FPGA design, including the system function logic, system control module, bus interface circuit and filter circuits,etc, FPGA peripheral circuit design. While programming DDS waveform synthesis circuit, adopted pipelined approach to improve DDS circuit structure, which extended its output bandwidth. Based on deeply studying the principle of various modulation signals, realizing AM, FM, FSK, sweep frequency and burst,etc, modulation function modules, directly realizing the signal modulation output by using digital method. On this basis, through the design of bus interface circuit and system instruction set, it realized SOPC hardware system integration of the signal generator, and also finished system related test software design.After the test, it shows that the system output signal frequency resolution can achieve 30mHz, its highest output frequency can reach 30MHz under 125MHz data sampling rate of DAC, frequency accuracy is better than 0.1%. The output signal amplitude characteristic remains intact when connects 50Ωload at the output terminal. Output signal harmonic distortion reached-60dB when the output signal bellows 2MHz, while overall system output waveform harmonic distortion is better than-36dB, which can well meet the needs of system test.