Master shows: the process of making an oscilloscope with high refresh rate!

Many oscilloscope users are all concerned about the refresh rate indicator of the oscilloscope. In fact, the refresh rate indicator of the oscilloscope is very important! The refresh rate of the oscilloscope directly determines the ability to capture abnormal glitches. Only by truly mastering the essence of the refresh rate can we correctly understand the refresh rate indicator of the oscilloscope. Many oscilloscope users are all concerned about the refresh rate indicator of the oscilloscope. Recently, when our FAE communicated with customers, many customers were very interested in the high refresh rate of 330,000 frames/second of the ZDS2022 oscilloscope. How is such a high refresh rate made?  What is the waveform refresh rate? The waveform refresh rate is also called the waveform capture rate, which refers to the number of waveform refreshes per second, expressed as waveforms per second (wfms/s). In fact, the process of the oscilloscope from acquiring the signal to displaying the signal waveform on the screen is composed of several capture cycles. A capture cycle includes sampling time and dead time. The analog signal is sampled and quantized by the ADC and converted into a digital signal and stored at the same time. The time of the entire sampling and storage process is called the sampling time. The oscilloscope must perform measurement, calculation, display and other processing on the stored data before starting the next sampling. This period of time is called the dead time. During the dead time, the oscilloscope does not perform waveform acquisition. When one capture cycle is completed, it will enter the next capture cycle. The reciprocal of the capture cycle is the waveform refresh rate, as shown in Figure 1.1, the waveform refresh rate = 1/(Tacq + Tdeat).   
Figure 1.1 Schematic diagram of the oscilloscope sampling process What are the factors that affect the waveform refresh rate? Sampling time and dead time As shown in Figure 1.1, the waveform refresh rate is the reciprocal of Tacq (sampling time) and Tdeat (dead time), where the sampling time is determined by the sampling window of the oscilloscope screen, which is multiplied by the horizontal base gear by the number of horizontal grids. When the horizontal time base is determined, the sampling time will be fixed. The dead time is determined by the processing power of the oscilloscope. When the oscilloscope's data processing capacity is insufficient, the collected big data cannot be processed in time, the dead time will become longer, and the refresh rate will be reduced; when the oscilloscope's data processing capacity is very strong, the dead time will become shorter, and the corresponding refresh rate will be very high. Therefore, the dead time is an important factor affecting the refresh rate. Increasing the trigger holdoff time is equivalent to increasing the dead time in disguise, because during the holdoff period, the trigger circuit is closed and the trigger function is suspended. Even if there is a signal waveform that meets the trigger conditions, the oscilloscope will not trigger, so it will also affect the refresh rate. But the trigger holdoff time does not refer to the dead time.
When triggering a large-cycle repetitive waveform, the trigger waveform is unstable because there are many waveform points in the waveform that meet the trigger conditions. In order to obtain a stable triggered waveform, we can set the trigger holdoff time so that the waveform is triggered at the same point each time and the triggered waveform is displayed stably. As shown in Figure 1.2, the holdoff time can be set to a value >200ns but <600ns.   
Figure 1.2 Trigger holdoff time
How to calculate the dead time?

How is the dead time, which has an important impact on the refresh rate, calculated? When capturing an abnormal pulse with a pulse width of 40ns~60ns, the appropriate horizontal time base gear can be set at 50ns/grid. At this time, the ZDS2022 oscilloscope has a waveform refresh rate of 330,000 frames/second, which means that the total capture time occupied by each trigger sampling is T＝1s/330KHz=3.03us, and the effective sampling time is 50ns/divX14 (ZDS2022 oscilloscope has 14 grids in the horizontal direction) = 700ns. Then the dead time percentage is (3030-700)/3030=76.89%. To capture the same abnormal pulse, at the same time base position, if the T oscilloscope has a refresh rate of 50K frames/second, it means that the total time occupied by each trigger sampling is T=1S/50KHz=20us, and the effective sampling time is 50ns/divX10 (the oscilloscope has 10 grids in the horizontal direction) = 500ns, then the percentage of dead time is (20000-500)/20000=97.5%. The longer the dead time, the lower the probability of capturing occasional signals. When a small probability abnormal waveform appears in the dead time, the oscilloscope will not capture the abnormality, which will have a great impact on the debugging of the signal. How can the ZDS2022 oscilloscope achieve a high refresh rate
? So why can the ZDS2022 oscilloscope achieve a refresh rate of up to 330,000 frames/second? The dead time is as low as 76.89%, which is 21.13% lower than the 97.5% dead time of ordinary oscilloscopes!   
Figure 1.3 Waveform synthesizer block diagram The ZDS2022 oscilloscope uses ultra-large-scale FPGA for waveform synthesis, which is all hardware accelerated processing; The ZDS2022 oscilloscope uses ultra-large-scale FPGA integrated waveform display memory, high bus bandwidth, which greatly reduces data processing time, and adopts multi-threaded parallel processing; The waveform synthesis of the ZDS2022 oscilloscope is all processed by optimized algorithms. The ZDS2022 oscilloscope has a refresh rate of 330,000 frames/second, which can quickly capture waveform anomalies, efficient and practical! No matter how much you say, it is better to test it yourself!