An oscilloscope is a graphic display device that describes the waveform curve of an electrical signal. This simple signal waveform can show many features: signal time and voltage, the frequency of the oscillation signal circuit, signal represents a specific part of the "change" in the signal frequency relative to other parts of the, if there is a fault components make signal distortion, the signal of DC component (DC) and AC components (AC) values of noise, signal and noise changing with time comparison, multiple wave signals, etc.
At the beginning, it was mainly an analog oscilloscope
The forties of the 20th century was the era of the rise of electronic oscilloscopes. The development of radar and television required waveform observation tools with good performance. Teck successfully developed a synchronous oscilloscope with a bandwidth of 10MHz, which was the basis of modern oscilloscopes. The advent of semiconductors and electronic computers in the 1950s boosted the bandwidth of electronic oscilloscopes to 100MHz. In the 1960s, the United States, Japan, the United Kingdom and France made different contributions to the development of electronic oscilloscopes, including a sampling oscilloscope with a bandwidth of 6GHz, a traveling wave oscilloscope with a bandwidth of 4GHz, and a storage oscilloscope with a bandwidth of 1GHz.Portable, plug-in type oscilloscope becomes a series of products. In the 1970s, the analog electronic oscilloscope reached its peak, the spectrum series was very complete, the 1GHz multi-function plug-in oscilloscope marked the high level of science and technology at that time, and added logic oscilloscope and digital waveform recorder for testing digital circuit.Analog oscilloscope has not made greater progress since then, began to give way to digital oscilloscope, the United Kingdom and France even withdrew from the oscilloscope market, technology to the United States leading, low - and medium-grade products produced by Japan.
In order to improve the bandwidth of analog oscilloscope, oscilloscope tube, vertical amplification and horizontal scanning are needed. To improve the bandwidth of digital oscilloscope, only the performance of the front-end A/D converter needs to be improved, and there are no special requirements for oscilloscope tube and scanning circuit. In addition, the digital oscilloscope tube can make full use of memory, storage and processing, as well as a variety of trigger and pre-trigger capabilities. In the 1980s, digital oscilloscope emerged as a new force and made a lot of achievements.
However, some characteristics of analog oscilloscope in the early stage of development are not possessed by digital oscilloscope. Operation is simple: all operations can be found on the panel, waveform response in a timely manner, digital oscilloscope is often a longer processing time.
High vertical resolution: continuous and infinite level, digital oscilloscope resolution is generally only 8 to 10 bits.
Data update fast: every second to capture hundreds of thousands of waveform, digital oscilloscope every second to capture dozens of waveform.
Real-time bandwidth and real-time display: the bandwidth of continuous waveform and single waveform is the same, the bandwidth of digital oscilloscope is closely related to the sampling rate, the sampling rate is not high need to use interpolation calculation, easy to confuse waveform.
In short, the analog oscilloscope provides the engineering and technical personnel with the waveform of seeing is believing. The visual nerve of the human eye is very sensitive in the five senses. The screen waveform is instantly reflected to the brain to make decisions, and subtle changes can be sensed.Therefore, the beginning of the analog oscilloscope by the user's welcome.
Medium - term digital oscilloscope leads the way
The digital oscilloscope in the 1980s is in the transformation stage, and there are still many places to improve, TEK and HP companies in the United States have contributed to the development of digital oscilloscope. They later discontinued analog oscilloscopes and produced only digital ones with good performance. Into the 1990s, digital oscilloscope in addition to improve the bandwidth to more than 1GHz, more importantly, its overall performance beyond the analog oscilloscope. Appear so - called digital oscilloscope simulation phenomenon, in other words, try to absorb the advantages of analog oscilloscope, make digital oscilloscope better use.
The sampling rate of digital oscilloscope is increased from the initial sampling rate equal to two times of bandwidth to five or even ten times, and the distortion of sinusoidal wave sampling is reduced from 100% to 3% or even 1%. The sampling rate for bandwidth of 1GHz is 5GHz/s, even 10GHz/s.
Secondly, the update rate of digital oscilloscope is improved to reach the same level as that of analog oscilloscope, with a maximum of 400,000 waveforms per second, greatly enhancing the ability of observing accidental signals and capturing burr pulses.
Thirdly, the use of multiprocessors to speed up the signal processing capacity, from the multimenu cumbersome measurement parameters adjustment, improved to a simple knob adjustment, or even fully automatic measurement, use and analog oscilloscope on the same convenient.
Finally, digital oscilloscope and analog oscilloscope have the same display mode of afterglow on the screen, which gives the three-dimensional state of wave shape, that is, the signal amplitude, time and amplitude distribution in time. The digital oscilloscope with this function is called digital fluorescence oscilloscope or digital afterglow oscilloscope.
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.