Detailed explanation of oscilloscope parameters

One 、 bandwidth
bandwidth ： The difference between the single frequency signal amplitude measured by the oscilloscope and the actual amplitude value is less than 3dB The frequency range of .
The figure below 1 The horizontal axis of is the ratio of the measured signal frequency to the oscilloscope bandwidth , The vertical axis is the percentage of the measured amplitude and the actual amplitude of the signal . When the frequency of single frequency signal is equal to the bandwidth ratio of oscilloscope , The measured amplitude value is lower than the actual value 3dB. As you can see from the diagram , The measured amplitude value is always smaller than the actual amplitude value , To reduce the amplitude error , The ratio of signal frequency to oscilloscope bandwidth should be small enough .

Two 、 Sampling rate
Sampling rate ： Number of sampling points per unit time
We often see marks like this on the oscilloscope ：500MHz,4GSa/s. What is the relationship between sampling rate and bandwidth ？ The classical sampling theorem expresses such a meaning ： The original signal can be reconstructed only when the sampling rate is at least twice the maximum frequency of the signal . In other words, the sampling rate should be at least twice the bandwidth . If the bandwidth and sampling rate are not enough , You will not be able to catch very short spikes , Here's the picture 2：

3、 ... and 、 Storage depth
Storage depth ： The maximum number of sample points that can be stored , It depends on the storage capacity of the oscilloscope . Storage depth and recording time , The relationship between sampling rate is as follows ：
Storage depth = Capture time length × Current sampling rate
for instance ： The horizontal scale of the oscilloscope is adjusted to 100ms/div, The horizontal direction is 10 grid , The storage depth is 10M, The maximum sampling rate is 4G. The horizontal recording time is 100ms×10=1s, Sampling rate ×1s=10M, The sampling rate will be limited to 10M. Usually, the oscilloscope will automatically adjust the sampling rate .
Four 、 Waveform capture rate
Waveform capture rate ： The number of waveform refreshes per unit time .
As mentioned earlier , The sampling of oscilloscope is not continuous , But after sampling for a period of time , The collected data needs to be processed , Only after processing can we sample again . The time for the oscilloscope to capture a waveform includes data acquisition time and data processing time . In data processing time , The oscilloscope is “ Close eyes ” state , This period of time is called dead time . therefore , The digital oscilloscope can only measure part of the snapshot of the signal . Pictured 3

Compared with the waveform capture rate , The percentage of dead time in the acquisition cycle time is more important . In reality, most circuit faults occur with a very small probability , And the oscilloscope can only capture a small part of the signal , Most of the signals have been missed , The fault signal has a high probability of appearing in the missing signal . This brings us great difficulties in finding the fault . chart 4 It can help understand the influence of dead time .