An Ultra-High Timing Resolution Waveform Generator Based on Real-Time Computation and DDS

Direct digital synthesis (DDS) technology is widely used in test and measurement instruments, and DDS technology can easily synthesize various types of waveforms with high frequency switching speed, flexible waveform editing, and high frequency resolution. However, the internal timing characteristics of the waveform, such as pulse edge time, pulse width, and ramp symmetry, need the waveform samples rewritten into the waveform memory to achieve changes. The timing resolution of the waveform is also limited by the capacity of the waveform memory and the waveform sample rate, which is difficult to further improve. In this paper, we proposes a method for synthesizing pulses, squares and ramps with high timing resolution based on a combination of real-time computation and DDS. The timing resolution of the synthesized waveform is no longer limited by the waveform memory capacity and waveform sample rate. And the timing resolution of the waveform can be hundreds or thousands of times of the sampling period. Also, since the waveform samples are calculated in real time based on waveform parameters, it is easy to realize various modulations such as pulse width modulation (PWM), frequency modulation (FM), and amplitude modulation (AM). In the case of multi-channel output, high-resolution interchannel delay control can be achieved by precisely adjusting the waveform phases. A experimental prototype based on this method was designed. The prototype has four waveform output channels, each with a 2.5 GSPS waveform sample rate, and realizes a variety of waveform synthesis and modulation including pulse, square and ramp. The timing resolution can reach 0.1 ps, including interchannel delay, pulse edge time, pulse width, duty cycle and ramp symmetry.