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An oscilloscope is a widely used electronic measuring instrument. As the saying goes, electricity is invisible and intangible. However, an oscilloscope can help us “see” electrical signals, making it easier for people to study the changes in various electrical phenomena. Thus, the core function of an oscilloscope, as its name suggests, is to be an instrument that displays the waveform of electrical signals, allowing engineers to identify problems or assess system performance, among other things. There are also various definitions of waveforms, such as those in the time domain or frequency domain. For oscilloscopes, what is measured most often is the variation of voltage over time, that is, the waveform in the time domain. Therefore, the oscilloscope can analyze the voltage changes at the point under test, which enables its widespread use in various electronics industries and fields. In our industry, oscilloscopes are generally classified as either analog or digital oscilloscopes. Some manufacturers may give them other names in order to highlight a particular feature of their oscilloscopes, such as digital fluorescent oscilloscopes. Yet its fundamental principles still fall within these two main categories of oscilloscopes. An analog oscilloscope is a type of early oscilloscope that relies on an electron beam emitted by a cathode ray tube (also known as a picture tube, which was widely used in early televisions and monitors). This electron beam is directed at the fluorescent material on the screen through horizontal and vertical deflection systems, thereby displaying waveforms. However, at this point, the only advantage that analog oscilloscopes seem to have left is their price. It lacks the capability to store data and analyze waveforms; its triggering functions are limited as well, and it is unable to capture single or sporadic signals. Moreover, due to the use of numerous analog components within it, these components change over time as a result of temperature variations, which leads to unstable performance. Analog oscilloscopes have been almost completely phased out in modern electronic measurement, so what we will be discussing today are digital oscilloscopes. Early digital oscilloscopes, due to limitations in display technology, still used the CRT (Cathode Ray Tube) screens found in analog oscilloscopes. The main difference between digital oscilloscopes and analog oscilloscopes is that the input signal is not displayed directly on the screen; instead, it is sampled and digitized by an ADC (Analog to Digital Converter), stored in a cache, and then the data is retrieved through signal processing circuits. Since early digital oscilloscopes used CRT displays, it was also necessary to use a DAC digital-to-analog converter to convert digital signals into analog signals for display on the CRT screen. Modern digital oscilloscopes no longer use CRT displays in most cases; instead, they employ LCD screens. This not only reduces their size significantly, but some of them also offer more user-friendly touch controls. Moreover, there is no longer any need to convert digital sample points into analog signals. Since there is no fundamental difference between the two in terms of functional structure, the industry generally does not use terms such as CRT oscilloscope and LCD oscilloscope. Digital oscilloscopes are often referred to as digital storage oscilloscopes, as an important function of these devices is to store the data collected by the ADC. We can gain an intuitive understanding of the main process by which modern digital oscilloscopes collect data through the motherboard of this Mackox STO1104C intelligent oscilloscope: ① The signal is attenuated to an appropriate level by the probe and then sent to the front end of the oscilloscope. The maximum voltage that an oscilloscope can measure generally depends on the probe, which can reduce voltage signals of tens of thousands of volts to dozens of volts through attenuation. ②The signal reaches the front-end attenuator and amplifier through coupling circuits; on the oscilloscope software, this is achieved by adjusting the vertical scale so that the waveform fills the entire screen as much as possible, thereby improving vertical accuracy and leading to more precise measurements. The front-end section largely determines the first key parameter of an oscilloscope: bandwidth. ③The ARM processor controls the FPGA to adjust the sampling rate of the ADC converter; this is reflected in the oscilloscope software as a change in the time base. Since the storage depth is a fixed value, the sampling rate = storage depth ÷ waveform recording duration. Typically, changes to the time base are achieved by adjusting the sampling rate. Therefore, the sampling rate specified by the manufacturer is usually valid only under a specific time base setting; at larger time bases, due to the impact of the storage depth, the sampling rate has to be reduced. The ADC analog-to-digital converter and the RAM high-speed memory affect two other key parameters of an oscilloscope: the sampling rate and the storage depth. ④Next, the FPGA drives the ADC to perform synchronous sampling; the ADC then converts the collected data into binary form and writes it to the cache. The memory cache is what is referred to as the storage depth; generally, the size of the memory is four times that indicated by the oscilloscope for the storage depth. Since the FPGA cannot control the triggering of the oscilloscope, the signals collected are first twice the size of the indicated storage depth, and then a portion of this waveform is selected based on the triggering criteria. As a result, the oscilloscope can display the waveform prior to the triggering point. Furthermore, when the oscilloscope collects waveforms prior to filtering, the collection process must not be stopped, otherwise the waveform capture rate will be too low; therefore, it is also necessary to continue collecting sample points of the same length. Repeating this process results in a fourfold increase. ⑤Upon receiving the trigger command, the memory passes the data to the ARM processor for processing⑥. The ARM processor processes the data and then outputs it through the display interface to the screen for the user to see. Through calculations, the oscilloscope can also emulate multi-level brightness displays similar to those of analog oscilloscopes, as well as the color temperature display effect and afterglow effect unique to digital oscilloscopes. ⑦After processing the data, an oscilloscope can save the current waveform image or data to memory. It should be noted that this type of storage is completely different from the high-speed cache used for storing depth information; most oscilloscopes use external storage devices such as USB drives, SD cards, or computers. Some modern oscilloscopes come equipped with large built-in storage capacities, allowing data to be saved directly within the oscilloscope itself. In this process, ②③④ are all processed in parallel. Due to the processing speed limitations of digital oscilloscopes, it is not possible to ensure that the waveform of the signal being measured is displayed continuously in real time on the screen; data related to the waveform is lost between two consecutive displays, which is what is known as dead time. This is also the biggest drawback of digital oscilloscopes compared to analog oscilloscopes. However, as the computing power of oscilloscopes improves and the waveform capture rate increases, this drawback is gradually being addressed.