A brief discussion on the differences between analog oscilloscopes and digital oscilloscopes
To increase the bandwidth of analog oscilloscopes, oscilloscope tubes, vertical amplification and horizontal scanning need to be fully promoted. To improve the bandwidth of a digital oscilloscope, you only need to improve the performance of the front-end A/D converter, and there are no special requirements for the oscilloscope tube and scanning circuit. Plus digital oscilloscopes can make full use of memory, storage and processing, as well as multiple triggering and advance triggering capabilities. In the 1980s, digital oscilloscopes suddenly emerged and achieved numerous results. They have the potential to completely replace analog oscilloscopes. Analog oscilloscopes have indeed retreated from the front desk to the background.
However, some features of analog oscilloscopes are not available in digital oscilloscopes: simple operation - all operations are on the panel, and waveform response is timely. Digital oscilloscopes often require a longer processing time. High vertical resolution - continuous and infinite. The resolution of digital oscilloscopes is generally only 8 to 10 bits. Data updates quickly - hundreds of thousands of waveforms are captured per second, and digital oscilloscopes capture dozens of waveforms per second. Real-time bandwidth and real-time display - the bandwidth of continuous waveforms is the same as that of single waveforms. The bandwidth of digital oscilloscopes is closely related to the sampling rate. When the sampling rate is not high, interpolation calculation is required, which may easily lead to confusing waveforms.
In short, analog oscilloscopes provide engineers with waveforms that they can see and believe, allowing them to test with confidence within a specified bandwidth. Among the human facial features, eye vision is very sensitive. The screen waveform is instantly reflected to the brain for judgment, and even subtle changes can be perceived. Therefore, analog oscilloscopes are very popular among users.
Digital oscilloscopes first increase the sampling rate, from the initial sampling rate equal to twice the bandwidth to five or even ten times, and the distortion introduced to sine wave sampling is also reduced from 100% to 3% or even 1%. The sampling rate of a bandwidth of 1GHz is 5GHz, or even 10GHz. Secondly, increase the update rate of digital oscilloscopes to the same level as analog oscilloscopes, up to 400,000 waveforms per second, which will be much more convenient for observing occasional signals and capturing glitch pulses.
Thirdly, multi-processors are used to speed up signal processing capabilities, and the cumbersome measurement parameter adjustment from multiple menus is improved to simple knob adjustment, or even fully automatic measurement, and is as convenient to use as an analog oscilloscope. Finally, the digital oscilloscope, like the analog oscilloscope, has a screen persistence mode display, which gives the waveform a three-dimensional state, that is, it displays the amplitude, time and distribution of the amplitude in time of the signal. Digital oscilloscopes with this function are called digital phosphor oscilloscopes or digital persistence oscilloscopes.
Analog oscilloscopes use cathode ray oscilloscopes to display waveforms. The bandwidth of the oscilloscope is the same as that of the analog oscilloscope, that is, the speed of electron movement in the oscilloscope is proportional to the signal frequency. The higher the signal frequency, the faster the electron speed. The oscilloscope screen The brightness is inversely proportional to the speed of the electron beam. The low-frequency waveform has a high height and the high-frequency waveform has a low height. It is easy to obtain the third-dimensional information of the signal by using the brightness or grayscale of the fluorescent screen. If the vertical axis of the screen is used to represent amplitude and the horizontal axis is time, then the screen brightness can represent the change in signal amplitude distribution over time. This time-dependent fluorescence afterglow (grayscale scaling) effect is useful for observing mixed and sporadic waveforms. The analog storage oscilloscope is a representative product of this kind of dedicated oscilloscope. The highest performance reaches 800MHz bandwidth and can record fast transient events of about 1ns.
The digital oscilloscope lacks the persistence display function because it is digital processing and has only two states, either high or low. In principle, the waveform also displays "yes" and "no". In order to achieve multi-level brightness changes like an analog oscilloscope, a dedicated image processing chip must be used. For example, TEK uses a DPX processor chip, which has multiple functions such as data acquisition, image processing and storage. The DPX chip is composed of 1.3 million transistors. It adopts 0.65um CMOS process, parallel pipeline structure, and sampling rate of 2GS/s.
It is both a data acquisition chip and a raster scanner, simulating the luminescence characteristics of the oscilloscope screen phosphor, using 16 brightness levels to store the waveform on a 500*200 pixel LCD monochrome or color display every 0.33 seconds Update once. Since analog storage oscilloscopes can only rely on photographic films to record waveforms, they are not very convenient for data storage. For example, red represents the waveform with the highest probability of occurrence, and blue represents the waveform with the lowest probability of occurrence, so that it is clear at a glance. Since digital oscilloscopes have reached the 1GHz bandwidth level and combined with fluorescent display characteristics, their overall performance is better than analog storage oscilloscopes.
