Oscilloscope Sample Rate and Storage Depth Explained
Sampling, Sampling Rate
We know that computers can only handle discrete digital signals. In the analogue voltage signal into the oscilloscope facing the first problem is the continuous signal digitization (analog / digital conversion) problem. Generally from the continuous signal to the discrete signal process called sampling (sampling). Continuous signals must be sampled and quantified to be processed by the computer, therefore, sampling is the basis of digital oscilloscopes for waveform operations and analysis. By measuring the voltage amplitude of the waveform at equal time intervals, and the voltage is converted to eight binary code to represent the digital information, which is the digital storage oscilloscope sampling. The smaller the time interval between sampled voltages, the closer the reconstructed waveform is to the original signal. The sampling rate (sampling rate) is the sampling interval. For example, if the sampling rate of an oscilloscope is 10G times per second (10GSa/s), this means that samples are taken every 100ps.
According to the Nyquist Sampling Theorem, when sampling a band-limited signal with a maximum frequency of f, the sampling frequency SF must be more than twice as large as f in order to ensure that the original signal is completely reconstructed from the sampled value. Here, f is called the Nyquist frequency and 2 f is the Nyquist sampling rate. For a sine wave, at least two samples per cycle are required to ensure that the digitised pulse train can be more accurately reconstructed from the original waveform. If the sampling rate is lower than the Nyquist sampling rate, it will lead to the phenomenon of Aliasing.
Sampling Mode
When the signal into the DSO, all input signals in its A/D conversion before the need for sampling, sampling technology is generally divided into two categories: real-time mode and equivalent time mode.
Real-time sampling (real-time sampling) mode is used to capture non-repetitive or one-shot signals, using fixed time intervals for sampling. After triggering once, the oscilloscope samples the voltage continuously and then reconstructs the signal waveform based on the sampling points.
Equivalent-time sampling (equivalent-time sampling), is to sample the periodic waveform in different cycles, and then the sampling points are spliced together to reconstruct the waveform, (https://www.dgzj.com/ Electrician's Home) in order to get enough sampling points, multiple triggers are needed. Equivalent time sampling also includes sequential sampling and random repetitive sampling. The use of equivalent time sampling mode must meet two prerequisites: 1. The waveform must be repeated; 2. It must be able to be triggered stably.
The bandwidth of the oscilloscope in real-time sampling mode depends on the maximum sampling rate of the A/D converter and the interpolation algorithm used. That is, the real-time bandwidth of the oscilloscope is related to the A/D and interpolation algorithm used by the DSO.
Here another reference to the concept of real-time bandwidth, real-time bandwidth is also known as the effective storage bandwidth, is a digital storage oscilloscope using real-time sampling method when the bandwidth. So many bandwidth concepts may have been to see you crazy, here to sum up: DSO bandwidth is divided into analogue bandwidth and storage bandwidth. Usually we often say that the bandwidth refers to the analogue bandwidth of the oscilloscope, that is, the bandwidth of the oscilloscope panel is generally labelled. The storage bandwidth is the theoretical digital bandwidth calculated according to Nyquist's theorem, which is only a theoretical value.
