19 issues to pay attention to when using an oscilloscope

1. Is there any fixed relationship between bandwidth and sampling frequency?

The sampling rate should theoretically meet the sampling law of Nongxiaoxiang, that is, each cycle of the highest frequency signal of the measured signal should theoretically have at least 2 points, otherwise it will cause aliasing. But in reality, it also depends on many other factors, such as the waveform reconstruction algorithm. The Siglent series oscilloscope adopts advanced waveform reconstruction algorithm and is equipped with interpolation algorithm to accurately reconstruct the waveform. Generally speaking, the sampling rate is 4-5 times of the bandwidth to reproduce the waveform more accurately.

2. How to understand the bandwidth in oscilloscope indicators?

Bandwidth is a basic indicator of an oscilloscope. It is the same as the definition of amplifier bandwidth, which is the so-called -3dB point, that is, the frequency point when the amplitude of the oscilloscope is attenuated to 70.7% of the actual amplitude when a sine wave is added to the input of the oscilloscope is called bandwidth. In other words, using an oscilloscope with a bandwidth of 100MHz to measure a 1V, 100MHz sine wave, the amplitude obtained is only 0.707V. This is only the case of a sine wave. Therefore, when we choose an oscilloscope, in order to achieve a certain measurement accuracy, we should choose a bandwidth that is 5 times the highest frequency of the signal. Siglent's ADS1000CE oscilloscope provides a bandwidth of 300MHz and a real-time sampling rate of 2GSa/a, leading the domestic peer level.

3. Under the condition of a certain bandwidth, is it meaningless to have a too high sampling frequency?

Bandwidth is the basic condition for limiting the capture of high-frequency components of the measured signal. Since Siglent oscilloscopes use advanced waveform reconstruction algorithms and are equipped with interpolation algorithm displays, while providing a minimum real-time sampling rate of 500MS/s, it ensures perfect capture and true quantification of the trigger signal, and ultimately accurately reproduces the acquired signal.

4. What are the factors that affect the operating speed of an oscilloscope?

Simply put, the principles of oscilloscopes are similar. The front end is a data acquisition system, and the back end is computer processing. There are two main factors that affect the speed of the oscilloscope. One is the data transmission from the front end data acquisition to the back end processing, which is generally transmitted by bus, and the other is the back end processing method. Siglent oscilloscopes use mature high-speed hardware architecture, combined with DSP digital processing, which can effectively solve these bottlenecks and greatly improve the performance of the oscilloscope.

5. How to eliminate glitches when using an oscilloscope?

If the burr is inherent in the signal itself, and you want to use edge triggering to synchronize the signal (such as a sine signal), you can use the high-frequency suppression trigger mode, which can usually synchronize the signal. If the signal itself has burrs, but you want the oscilloscope to remove the burrs and not display the burrs, it is usually difficult to do so. You can try to use the bandwidth limitation method, but if you are not careful, you may also filter out part of the signal itself.

6. When choosing an oscilloscope, bandwidth is usually the most important consideration. So, under what circumstances should the sampling rate be considered?

It depends on the object to be measured. Under the premise of satisfying the bandwidth, it is hoped that the minimum sampling interval (the inverse of the sampling rate) can capture the signal details you need. There are also some empirical formulas for sampling rate in the industry, but they are basically derived for the bandwidth of the oscilloscope. In practical applications, it is best not to use an oscilloscope to measure the signal with bandwidth frequency. If you are selecting a model, for a sine wave, choose an oscilloscope with a bandwidth that is more than 3 times the frequency of the sine signal to be measured, and a sampling rate that is 4 to 5 times the bandwidth, which is actually 12 to 15 times the signal. For other waveforms, ensure that the sampling rate is sufficient to capture the signal details. If you are using an oscilloscope, you can verify whether the sampling rate is sufficient by the following method: stop the waveform, enlarge the waveform, and if you find that the waveform has changed (such as certain amplitudes), the sampling rate is not enough, otherwise it will not meet the measurement accuracy. You can also use point display to analyze whether the sampling rate is sufficient. The professional Siglent series oscilloscopes have solved the problem of bandwidth and sampling rate very well.

7. When it comes to observing waveform details, which one is more advantageous, analog or digital oscilloscope?

The vertical accuracy of the analog oscilloscopes we used in the early days was generally +/-3%, while the vertical accuracy of the digital oscilloscope is as high as +/-1%. In this respect, the digital oscilloscope has a great advantage. At the same time, the Siglent digital oscilloscope has different levels of brightness selection, which is more convenient and intuitive for displaying signal details.

8. How to capture and reproduce instantaneous signals that disappear in a flash?

To capture instantaneous signals, you can refer to the following settings: select edge as the trigger type, set the trigger mode to single, set the signal to rising trigger, and adjust the trigger level to an appropriate value. In addition, the Siglent oscilloscope is equipped with EasyZoom window expansion technology, which means that you can zoom in on local details while observing the overall signal.

9. Which type of oscilloscope should I choose to effectively improve design efficiency?

With the development of oscilloscopes, data analysis and processing have been greatly improved. Using an oscilloscope is not only to observe waveforms during debugging, but more importantly, it can be used to find problems in the design, analyze and calculate device parameters, and help you optimize the design. The most suitable oscilloscope should be determined based on the signal you want to observe and analyze. Siglent high-performance oscilloscopes provide 25M-300M bandwidth and 500MSa/s---2GSa/s sampling rates to meet your different needs.

10. What should I pay attention to when using the probe with an oscilloscope?

The probe is often ignored in the use of oscilloscopes. Passive probes are widely used because of their wide measurement range, low price, and ability to meet most measurement requirements. The selection of passive probes should be consistent with the bandwidth of the oscilloscope used. When replacing probes or switching channels, probe compensation must be adjusted to match the input channel. The simplest and most intuitive way to adjust probe compensation is to use the probe waveform.

11. What is the real-time sampling rate of an oscilloscope?

Real-time sampling refers to sampling the waveform at equal time intervals, performing A/D conversion in the order of sampling and storing it in memory. Real-time sampling is the most obvious and intuitive sampling method. This type of sampling only requires simply distributing sampling points in time, and all sampling points are obtained in response to a trigger of the oscilloscope. Siglent high-performance oscilloscopes provide real-time sampling rates of 500MSa/s---2GSa/s.

12. What is the equivalent time sampling of an oscilloscope?

Equivalent time sampling means that the oscilloscope combines the waveforms collected by multiple acquisitions (multiple triggers) into one waveform. The sampling rate may be very slow each time, and there is a certain offset between the two acquisition trigger points. The inverse of the minimum sampling interval between the two points is called the equivalent sampling rate. Its index can reach very high, such as 1ps. Siglent high-performance oscilloscopes have an equivalent sampling rate of up to 50Sa/s

13. When viewing waveforms on an oscilloscope, what is the difference between using external triggering and self-triggering?

The usual trigger of the oscilloscope is edge triggering, which has two triggering conditions, trigger level and trigger edge; that is, when the rising edge (or falling edge) of the signal reaches a certain level (trigger level), the oscilloscope triggers. The oscilloscope will only use external triggering when there is a problem with the self-triggering of the signal. There is no question of which is better. In addition, the signal is relatively complex, and there are many points that meet the trigger conditions. It is impossible to trigger at the same position every time to obtain a stable display. At this time, an external trigger is needed. Siglent ADS1000 oscilloscope provides standard dual channels + one external trigger channel

14. How to obtain the total bandwidth of the measurement system?

When measuring digital signals, the rise time of the signal determines the total bandwidth of the system. The total bandwidth of the measurement system = 0.35/rise time

15. How to apply trigger holdoff in measurement? What is its function?

Trigger holdoff means temporarily closing the trigger circuit of the oscilloscope for a period of time (i.e., holdoff time). During this period of time, the oscilloscope will not trigger even if there are signal waveform points that meet the trigger conditions. The function of the trigger part of the oscilloscope is to display the waveform stably, and trigger holdoff is also a function set to display the waveform stably. It is mainly set specifically for large-cycle repetitions and there are many non-repeating waveform points that meet the trigger conditions in the large cycle. Siglent oscilloscopes provide an ultra-long trigger holdoff time of 100ns---1.5s.