How do I measure the refresh rate of an oscilloscope?

Preparation tools: oscilloscope under test, measuring instruments (oscilloscope, logic analyzer, MHz signal source.

The oscilloscope outputs a pulse signal at the trig out for each waveform sampled, and this trig out interface is usually on the back of the oscilloscope, so we can measure the trig out signal to measure the waveform refresh rate of the oscilloscope. We want to measure the waveform refresh rate of the ZDS4000 oscilloscope this time, and use the ZDS1000 as the measuring instrument, where the ZDS4000 is connected to the 20MHz signal source, and the ZDS1000 is connected to the ZDS4000 trig out signal.

Oscilloscope settings.

The nominal waveform refresh rate of an oscilloscope is usually the maximum, but in fact the refresh rate of the base gear is inconsistent for each level, and we need to find the time base stop with the largest refresh rate. First of all, the ZDS4000 display type is set to a point, the ZDS1000 turns on the hardware frequency meter, measures the TRIG OUT signal frequency of the ZDS4000 in real time, and then rotates the ZDS4000 horizontal time base from the minimum gear 500PS to the large, observes the TRIG OUT frequency, and finds the maximum value.

Refresh rate calculations.

Many people directly use the trig out frequency as the waveform refresh rate, which is actually inaccurate, because the waveform refresh rate refers to the number of waveform captures per second, and some oscilloscopes trig out are intermittent and some are continuous, and the best way is to count the number of pulses in a second of trig out to be the accurate waveform refresh rate. Turn on the ZDS1000 statistical measurement function, set the horizontal time base to 100ms gear, and the total sampling time is RiseCount rising edge counter, which is equivalent to about 1s, indicating that the maximum refresh rate of ZDS4000 oscilloscope is.

Pick up the oscilloscope in your hand and test it, the higher the waveform refresh rate, the shorter the dead time.

The refresh rate of the waveform is related to the sampling time and dead time, as well as the trigger release time, the dead time is the key factor to determine the refresh rate, and the dead time is related to the data processing ability of the oscilloscope itself.

How to measure the waveform capture rate of an oscilloscope.

The oscilloscope collects signals and displays them on the screen, while the signals he collects are dotted one by one. The number of points that can be installed on a screen of the oscilloscope is the storage depth of the oscilloscope. So how many points per second can an oscilloscope collect? This is the sample rate of the oscilloscope.

Since: storage depth = sampling rate * waveform duration, it can be seen that the sampling rate changes with the waveform duration in real time (the storage depth is fixed).

Generally, the current storage depth and sample rate of the oscilloscope will also be displayed on the oscilloscope. The unit of sampling rate is sa s, and sa is the abbreviation of sample, which is actually the meaning of sampling point.

In most cases, the higher the refresh rate, the better, but also consider the depth of storage. The following ** is a comparison of refresh rates at home and abroad**.

a. Traditional oscilloscope waveform synthesizer scheme.

Disadvantages: Limited by asynchronous bus bandwidth and DSP processing power, the waveform refresh rate is low, typically less than 5,000 frames per second.

b. Domestic brand oscilloscope waveform synthesizer scheme.

Disadvantages: The video memory uses external SSRAM, the bus bandwidth is limited, and the waveform refresh rate is difficult to break through, usually less than 200,000 frames per second.

c. International brand oscilloscope waveform synthesizer scheme.

Advantages: use of dedicated ASIC, integrated waveform memory, high bus bandwidth, high refresh rate. Disadvantages: The sampling memory is limited by the ASIC area, and the storage capacity is small, so it cannot be stored deeply. •

d. Zhiyuan electronic oscilloscope waveform synthesizer scheme.

Advantages: Large-scale FPGA multi-threaded parallel processing, integrated waveform memory, high bus bandwidth, refresh rate up to 330,000 frames per second; External large-capacity DDR3 memory for deep storage.

The waveform refresh rate is an important technical indicator of the oscilloscope, which directly reflects the oscilloscope's ability to capture waveform details. The higher the waveform refresh rate, the shorter the dead time, and the higher the probability of catching abnormal signals. The figure below shows that the ZDS2022 desktop oscilloscope of Zhiyuan Electronics captures an abnormal signal with a low probability of occurrence, as shown by the dim waveform in the figure, and it is difficult for the oscilloscope with low refresh rate to capture such signals.

Hope it helps.

The waveform refresh rate is an important indicator of the oscilloscope, which together with the sampling rate directly reflects the oscilloscope's ability to capture the details of the waveform, and the mainstream oscilloscopes on the market are more than 10000wfms s (typical value). However, this metric is generally given by oscilloscope manufacturers, and few articles mention how to test this indicator, resulting in users not being able to really measure it. In this article, we'll introduce a simple method for getting a rough estimate of the oscilloscope's refresh rate. Reference.