How to choose digital oscilloscope?
How to choose oscilloscope reasonably as the price difference of oscilloscope nearly 50 times between low-grade with high-grade.
The relationship between the bandwidth selection and the highest signal frequency to be measured is needed if accurate measurements are required. Let’s check below example, there is one pulse signal with 50 MHZ, to ensure scope of signal and accuracy of rising delay, the bandwidth of oscilloscope should be 3-5 times of measured signal’s frequency and the accurate measurement should be 8-10 times or more.
Sine wave: as usual, need more than 5 sampling sites during one period as the waveform will be more close to the actual one with more sampling sites.
Pulse wave: rising delay should be more than 5 sampling sites.
Accurate measurement rising delay should be more than 10 sampling sites.
3. Record length: record length=sample*scanning speed*10, it could also be called waveform observation time.
4. Trigger function: ensure that the measured signal can be captured and synchronized to facilitate the observation and analysis of the measured waveform
Trigger methods: automatic trigger, normal trigger and single trigger
Two kinds of trigger function
1) Edge trigger: all digital oscilloscopes have this function, It refers to positive edge, negative edge trigger, window trigger, before trigger and after trigger.
2）Smart trigger：This is considered perfectly in high-grade oscilloscopes. currently there are: delay trigger, sequence trigger, burr trigger, interval trigger, leakage logic surface trigger, TV trigger, this trigger......
5. Analysis function: Should have very strong automatic processing, computation, test and analysis ability of signal
1）Shape and parameters pass/fail automatic test function
2) Advanced function processing: average, differential, polar, exponential, logarithm, power, square root, envelope, high score system, etc.
3）FFT spectrum operation function from 10k-4m point, with power spectrum, power density, phase vector, imaginary part, real part and other measurements;
4）The direct square analysis can be used for the stability calculation of the direct square test signal from 500 points to 8M points according to various parameters
5）Waveform parameter Trend analysis function, Jitter and time analysis;
6) Could open 2-8 windows to observe original waveform and processed waveform simultaneously.
X-Y display and X-Y+X-T and Y-T display are provided, can also carry on the vernier measurement makes it specially suitable for vector diagram analysis of digital communication signals.
6. Record and print signal
1) Can be stored in a test line on a floppy and hard disk, and can be read on a PC. Some digital oscilloscopes are equipped with built-in, convenient to print and analyze long time signal;
2) Some oscilloscopes also provide VGA interface.
Under what circumstances should oscilloscope consider the sampling rate?
The bandwidth is dependent on the object under test. You want the minimum sampling interval (the inverse of the sampling rate) to capture the signal details you need, provided the bandwidth is satisfied. There are some empirical formulas about sampling rate in the industry, but basically they are all based on oscilloscope bandwidth, in practical application, it is best not to use oscilloscope to measure the same frequency signal. When selecting the type, the bandwidth of the oscilloscope should be more than 3 times that of the measured sinusoidal signal, and the sampling rate should be 4 to 5 times that of the bandwidth, which is actually 12 to 15 times that of the signal.For other waveforms, ensure that the sampling rate is sufficient to capture signal details. If you are using an oscilloscope, you can verify that the sampling rate is sufficient by stopping the waveform, amplifying the waveform, and if there is any change in the waveform (such as some amplitude), the sampling rate is insufficient, otherwise it will be ok. Point displays can also be used to analyze the adequacy of the sampling rate.
DPO and development of oscilloscope technology
The application of digital fluorescence display technology enables DPO to simultaneously display multiple images of signals in different shades or colors. DPO clock can record 200,000 waveforms per second, and its signal data is 1000 times more than ordinary DSO, and each time can capture 500,000 waveforms. This fast waveform acquisition rate combined with excellent display ability enables DPO to analyze any detail of the signal.
Usually DSO for processing display data in the display between two waveforms have 8 ms dead time, even if the sampling technologies adopted instavuTM DSO this time also can reduce to 1.7 mu s, ART cannot capture the waveform oscilloscope in flyback time information and DPO can always at the highest sampling rate of continuous sampling of hundreds of thousands of waveforms, overcome the other between stagnation into the problems of the oscilloscope. The sampling rate of DPO generally has several 109 times per second, which allows oscilloscope to have larger bandwidth.