High-Speed Digitizing of Repetitive Waveforms Using Accurate Interleaved Sampling

Random interleaved sampling has become a widespread operating mode for digital storage oscilloscopes. Different repetitions of (notionally) the same waveform are recorded at random time shifts and are interleaved in memory, resulting in an increase of the equivalent sampling frequency. This procedure requires substantial time, particularly if further averaging is required. In this paper, an approach that ensures accurate time shifts is presented for repeated waveform measurements. Operating two independent oscillators with related frequencies forms the accurate shifts. One of these is used to excite a waveform of interest repeatedly, and the other clocks the analog-to-digital converter (ADC). This architecture was implemented using a commercial "off-the-shelf" field programmable gate array. Examples of experimental waveforms, which are sampled at 2160 MHz using an ADC that is clocked at 80 MHz, are presented. They are compared with the simulated and independently measured waveforms where appropriate.