How to verify the waveform refresh rate of an oscilloscope

Many engineers often find such a problem: they did not find any abnormalities in the debugging process of the circuit board they made, but found various problems or failures soon after using it. The main reason is that the abnormal signal was not correctly captured during the debugging process, resulting in incorrect measurement results. So how can you see the abnormal signal at a glance during debugging? This actually tests the waveform refresh rate of the oscilloscope.

The waveform refresh rate, or waveform capture rate, refers to the number of waveforms captured per second, expressed as waveforms per second (wfms/s).

In fact, the process from acquiring signals to displaying waveforms on the screen consists of several capture cycles.

One capture cycle consists of sampling time and dead time.

Sampling time refers to the process of converting analog signals into digital signals and storing them.

Dead time refers to the process in which the oscilloscope measures, calculates, displays, and processes the sampled and stored digital signals. The oscilloscope does not collect data during the dead time.

It can be seen that the size of the dead time will affect the length of the capture cycle and thus affect the waveform refresh rate. As shown in the following figure:

Figure 1 The impact of different refresh rates on dead time

As can be seen from the figure, an oscilloscope with a higher waveform refresh rate has a shorter dead time, which means it has a higher chance of capturing low-probability abnormal signals in the waveform. However, an oscilloscope with a low refresh rate takes a long time to capture low-probability abnormal signals due to its longer dead time. This is why sometimes the circuit is obviously faulty but the waveform on the oscilloscope looks completely normal. We can look at a comparison chart, as shown below:

Figure 2 Dynamic diagram of 5kwfms/s signal with glitches

Figure 3 Dynamic diagram of a 330k wfms/s signal with glitches

The advantages of high waveform refresh rate can be clearly seen from the two dynamic comparison charts. Therefore, when users buy oscilloscopes, waveform refresh rate is an important factor that you must consider. Under certain conditions, the higher the waveform refresh rate, the better. Especially when doing signal integrity analysis, if the abnormal signal is not captured, it will affect your test results. The ZDS2000 series oscilloscope can reach a maximum waveform refresh rate of 330kwfms/s, the highest in the industry.

Through the above understanding of the waveform refresh rate, we can verify the waveform refresh rate. Take the ZDS2022 oscilloscope as an example. First, connect a 1M square wave signal, capture the normal waveform with one click, click [Display] to change the display type to point display, adjust the time base gear to 50ns/div, and let the full screen capture 700ns; click [Measure], open the measurement statistics, click the trigger counter in the measurement option, that is, the number of times the waveform is triggered per second. Similarly, the waveform refresh rate of 330kwfms/s can be measured. As shown in the figure below:

Figure 4 Verifying the maximum waveform refresh rate of the oscilloscope

The waveform refresh rate is related to the time base, and different models of oscilloscopes have different time bases for measuring the maximum waveform refresh rate. For example, the DPO2000 series manual of T company nominally has a maximum waveform refresh rate of 5.5kwfms/s. When verifying the maximum waveform refresh rate, adjust the time base to 200ns/div.

In summary, you should have a certain understanding of the waveform refresh rate of the oscilloscope. The ZDS2000 series oscilloscopes of Guangzhou Zhiyuan Electronics use large-scale FPGA technology and full hardware accelerated parallel processing to create a new high in waveform refresh rate, up to 330,000 times per second, which is much higher than the same-level products of the same industry. The dead time is shorter and the probability of capturing abnormal signals is higher. You deserve it.