Digital electronic oscilloscope circuit application and design solutions
Electronic oscilloscopes are instruments widely used by engineers in laboratories, factories and on-site. In fact, electronic oscilloscopes are also the products with the largest sales volume and the highest sales volume among electronic test and measurement instruments. From the late 1930s to the early 1940s, driven by the rapidly developing markets of television broadcasting and radar ranging, the analog electronic oscilloscope was basically finalized and divided into four parts: vertical amplification, horizontal scanning, trigger synchronization and oscilloscope tube (CRT) display. . The real-time bandwidth of analog electronic oscilloscopes reached a peak of 1000MHz in the 1970s. With the emergence of digital technology and integrated circuits, analog electronic oscilloscopes dominated by vacuum tubes and broadband amplifier circuits were gradually replaced by digital electronic oscilloscopes starting in the 1980s. With the explosive development of information technology and digital communication markets, the real-time bandwidth of digital electronic oscilloscopes exceeded 1GHz in the 1990s. In the 2010s of the 21st century, digital electronic oscilloscopes have also made a leap forward, with real-time bandwidth exceeding 10GHz and equivalent sampling bandwidth reaching 100GHz.
The circuit structure of a digital electronic oscilloscope is simpler than that of an analog electronic oscilloscope. It mainly consists of four parts: analog/digital converter (ADC), waveform storage/processor, digital/analog converter (DAC) and liquid crystal (LCD) waveform display. Analog electronic oscilloscopes need to have a broadband response from the signal input front end to the waveform display back end. However, digital electronic oscilloscopes only need the front-end analog/digital converter to have the same broadband response as the input signal, and then the frequency response of various circuits is reduced accordingly. According to the sampling principle, under optimal conditions, the sampling frequency is equal to 2 times the highest frequency of the input analog signal. After the ADC output digital information is filtered and processed by the DAC, the waveform of the input signal can be reproduced. Obviously, the DAC clock frequency can be much lower than the ADC sampling frequency. In addition, in order to reduce aliasing signals caused by signal filtering and processing, the actual sampling frequency used by the ADC of the digital electronic oscilloscope is 4 times rather than 2 times the highest frequency of the analog input signal.
Currently, the highest level ADC sampling frequency reaches 20GHz and resolution is 8 bits. If two ADCs with a sampling frequency of 20GHz are used and superimposed on the time axis, an equivalent ADC function with a resolution of 8 bits and a sampling frequency of 40GHz will be obtained. In other words, with an ADC with a sampling frequency of 20GHz, an implementation bandwidth of 10GHz can be achieved, but the resolution is only 8 bits. If the sampling rate of the ADC is allowed to be reduced, it is not difficult to increase the resolution of the ADC. For example, an ADC with a 1MHz sampling rate can achieve 28-bit resolution. Digital electronic oscilloscopes with a real-time bandwidth of more than 100MHz fully adopt 8-bit resolution. In order to improve the resolution, multiple samplings can be averaged, but the measurement time also increases accordingly. Digital electronic oscilloscopes with a real-time bandwidth of less than 100MHz can provide products with resolutions of 8-bit, 10-bit, and 16-bit or more.
