Design and implementation of a ultra-high timing resolution pulse generator based on real-time computation

Abstract

In the field of automatic test systems, direct digital synthesis (DDS) technology plays a crucial role with features such as fast frequency switching speed, high-frequency resolution, and flexible waveforms. However, the timing resolution of the pulse waveform generated by DDS technology is limited by the storage depth of waveform memory and sampling rate. DDS generates a maximum 1 clock cycle jitter in the pulse waveform as the frequency tune word (FTW) changes driven by the sampling clock, and the pulse width modulation (PWM) of the pulse waveform is not possible with DDS technology. In this paper, a parallel pulse waveform synthesis method based on real-time computation is proposed. The pulse waveform generated by this method has a timing resolution that far exceeds the sampling period including rising time resolution, falling time resolution, pulse width resolution, and delay resolution. Since the pulse parameters such as rising time, falling time, and pulse width can be independently adjusted with phase continuity, and the waveform samples are generated by real-time computation, the method can easily implement PWM and various modulations. The waveform samples computed in real-time correspond precisely to their theoretical phases with extremely low phase truncation error, thus jitter is greatly reduced and the timing resolution can be significantly improved. In this paper, based on the real-time computation of waveform samples, the sampling rate is increased eight times by parallelizing the computation. Each computing channel is run at 156.25 MHz, and the sampling rate of 1.25 GSPS waveform samples is achieved by running in parallel with eight channels. Finally, the pulse waveform is generated with a timing resolution of 0.2 ps, which theoretically requires a sampling rate of 5 TSPS to achieve.