How is the bandwidth?
Bandwidth is generally defined as the frequency when the amplitude of sinusoidal input signal attenuates to -3db, that is, 70.7%. Bandwidth determines the basic measuring ability of oscilloscope to signal. With the increase of the signal frequency, the oscilloscope's ability to display the signal accurately will decline, if there is not enough bandwidth, the oscilloscope will not be able to distinguish the high-frequency change. The amplitude will be distorted, the edges will disappear, and the details will be lost. Without sufficient bandwidth, all the properties of the signal obtained, such as ringing and singing, are meaningless.
A rule of thumb for determining the bandwidth effectiveness of the oscilloscope you need is the "5x rule"; Multiply the highest frequency component of the signal you want to measure by 5. This will give you an accuracy of more than 2% in your measurements
In some applications, you do not know the bandwidth of the signal you are interested in, but you know the fastest rise time, most digital oscilloscopes use the following formula to calculate the associated bandwidth and the rise time of the instrument: bandwidth = 0.35 ÷ the fastest rise time of the signal.
There are too kinds of bandwidths: repeat (or equivalent time) bandwidth and real time (or single time ) bandwidth. Repeat bandwidth is only applicable for repeat signals to display comes from sampling during multiple signal acquisition. Real-time bandwidth is the highest frequency that can be captured in a single sample of oscilloscope, and the requirements are quite demanding when the captured events do not often occur. Real-time bandwidth is associated with sampling rates.
Since wider bandwidth tends to mean higher prices, evaluate the frequency components of the signals you normally look at against your budget.
How is the sampling rate?
Defined as sampling times per second (Sa/s), the frequency of signal sampling by exponential oscilloscope. The higher the sampling rate of the oscilloscope, the higher the resolution and clarity of the waveform displayed, and the lower the probability of important information and events being lost.
The minimum sampling rate becomes important if the slow signal over a long time range is observed. In order to maintain a fixed waveform number in the displayed waveform record, the horizontal control button needs to be adjusted, and the displayed sampling rate will also change with the adjustment of the horizontal control button.
How to calculate sampling rate? Measuring method depends on the waveform measured and the signal reconstruction method adopted by oscilloscope.
To reproduce the signal accurately and avoid confusion, the Nyquist theorem states that the sampling rate of the signal must be no less than twice its highest frequency component. However, the premise of this theorem is based on infinitely long and continuous signals. Since no oscilloscope can provide a record length of infinite time and, by definition, low-frequency interference is discontinuous, sampling rates of twice the highest frequency components are usually insufficient.
In fact, the accurate reproduction of signal depends on its sampling rate and the interpolation method used in the gap of signal sampling points. Some oscilloscope will provide following choice to operator: sinusoidal interpolation method for measuring sinusoidal signal, and linear interpolation method for measuring rectangular wave, pulse and other signal types.
There is a useful rule of thumb for comparing sample rates and signal bandwidths: if the oscilloscope you are looking at has interpolation (filtered to regenerate between sampling points), the ratio (sampling rate/signal bandwidth) should be at least 4∶1. Without sine interpolation, the ratio of 10∶1 should be adopted.
How fast does the screen refresh?
All oscilloscopes flash. That is to say, the oscilloscope captures the signal at a certain number of times per second, and the measurement between these measuring points is no longer carried out. This is the waveform capture rate, also known as screen refresh rate, expressed as the number of waves per second (WFMS /s). Sampling rate represents the frequency of input signal sampled by oscilloscope in a waveform or period.Waveform acquisition rate refers to the oscilloscope acquisition waveform speed. Waveform acquisition rate depends on the type and performance level of oscilloscope, and has a large range of changes. The oscilloscope with high wave acquisition rate will provide more important signal characteristics and greatly increase the probability of the oscilloscope to quickly capture instantaneous abnormal conditions, such as jitter, short pulse, low frequency interference and instantaneous error.
Digital storage oscilloscope (DSO) can capture 10 to 5,000 waveforms per second using a serial processing structure. DPO digital fluorescence oscilloscope USES parallel processing structure, can provide higher waveform capture rate, some up to millions of waves per second, greatly improve the possibility of intermittent capture and difficult to capture events, and allow you to find the signal problems faster.