Study About Key Techniques Of Synthesizing High-speed Arbitrary Waveform

With the development of electronic technology, the frequency and complexity of system under test increase rapidly. Thus the higher requirments on bandwidth and variaty of stimulus signals are put forword. The method that is used to generate arbitrary waveform based on direct digital synthesis, which has outstanding advantages such as flexible waveform, high frequency resolution and fast frequency switching speed is applied in modern time-domain tests field widely.The development of arbitrary waveform synthesis that is the reverse process of signal acquisition is inseparable from the development of memory technology and signal sampling, mainly reflecting in high sampling rate, deep memory and excellent waveform performance, etc. In association with the relevant research projects during the Ph.D. study, subsequently, the key techniques of increasing sampling rate, improving output waveform quality, and allowing high-precision synchronization in arbitrary waveform synthesis were studied.1. The study of the arbitrary waveform synthesis based upon DDFS and DDWS. The principles, hardware structures, and their advantages and disadvantages of the two direct digital synthesis methods (DDFS and DDWS) were analyzed. The applications of the two methods to the arbitrary waveform synthesis were discussed. Based on the above, the DDS sampling model was built to analyze the characteristics of the frequency spectrum of their output signals.2. Increasing of the sampling rate of arbitrary waveform by means of parallel memory. The choke points of increasing the sampling rate in synthesizing high-speed arbitrary waveform were discussed. A method of increasing frequency of memory and accumulator with multi-memories in parallel was analyzed. The expressions of the frequency tunning word and frequency resolution in synthesizing were put forward.3. Enhancing the sampling rate of arbitrary waveform by means of multi-DDS parallel pseudo interleaving. For increasing the sampling rate of DAC, a method of arbitrary waveform synthesis by means of multi-DDS pseudo interleaving was proposed. And then the method was proven to be feasible in time domain and frequency domain. The limitation of DDS channels in pseudo interleaving parallel synthesis because of DAC hold characteristics was analyzed. The method on selecting DAC was discussed.4. Improving the quality of the output waveform with multi-DDS parallel pseudo interleaving. The errors of the multi-DDS parallel pseudo interleaving arbitrary waveform synthesis were researched and the error model was built. DAC hold characteristics error, phase truncation error, clock phase deviation error and amplitude quantization error were analyzed and discussed in details. Then some error correcting methods were proposed and were proven to be feasible in experiments.5. Developing precise phase adjustment and synchronization techniques. The structure of multi-channel arbitrary waveform generator was researched. The method, range and precision of the phase adjustment in synthesizing were discussed. The timing model of the sampling clock and synchronous trigger signal of each function module in precision synchronization was studied. The method of high-precision synchronization with embedded phase self-calibration module was put forward. And it was proven to be feasible in experiments.6. Presenting durable high-speed arbitrary waveform synthesis. The arbitrary waveform synthesis based upon SDRAM which meet the high-capacity memory requirement of arbitrary waveform was analyzed. The arbitrary waveform synthesis based upon sequence mode in term of the specific waveform with numerous repeated redundant samples was researched. A method of synthesizing durable high-speed arbitrary waveform was presented. The timing parameter was caculated and the design of high resolution clock generator was discussed.