Digital oscilloscope should have analog function
Analog oscilloscope waveform with a cathode ray tube display, the bandwidth of the oscilloscope tube the same as the analog oscilloscope, i.e. oscilloscope tube electronic speed is proportional to the signal frequency, signal frequency, the higher the faster the electrons, oscilloscope tube screen brightness is inversely proportional to the speed of electron beam, low frequency waveform of high brightness, high frequency waveform of the low brightness. The third dimension information of the signal can be easily obtained by using the brightness or grayscale of the fluorescent screen. If the vertical axis of the screen represents the amplitude and the horizontal axis represents the time, the screen brightness can represent the change of the signal amplitude with the time distribution. This time-related fluorescence afterglow (gray scale scaling) effect is very effective for the observation of mixed waveform and occasional waveform. The analog storage oscilloscope is the representative product of this special oscilloscope, with the highest performance up to 800MHz bandwidth, and can record the rapid transient accidental events around 1ns.
Digital oscilloscope lack of afterglow display function, because it is digital processing, only two states, either high or low, in principle waveform is "there" and "no" two display. In order to achieve the multi-layer luminescence change like the analog oscilloscope, special image processing chip must be used. For example, TEK company adopts DPX processor chip, which has many functions such as data acquisition, image processing and storage. DPX chip is composed of 1.3 million transistors and adopts 0.65 micron CMOS process. It is not only a data acquisition chip, but also a grating scanner. It simulates the luminescence characteristics of the oscillotube screen fluorescent body, USES 16 levels of brightness classification, and stores the waveform on the 500×200 pixel LCD monochrome or color display screen, updated every 1/30 seconds. Since analog storage oscilloscope can only rely on photographic film to record waveform, it is not convenient for data preservation, while digital fluorescence oscilloscope is the display of digital processing, data recording, processing and preservation are very convenient. For example, red represents the highest probability of waveform, blue represents the lowest probability of waveform, to be clear at a glance. Because the digital oscilloscope has reached the level of bandwidth above 4GHz, combined with the fluorescence display characteristics, the overall performance is better than the analog storage oscilloscope.