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.
Are the different oscilloscope probes interchangeable?
It's interchangeable as long as it's the same interface
Note, however, that the matching capacitance of the probe matches that of the oscilloscope
So maybe it needs to be adjusted
The other is impedance matching of the probe.The impedance matching part of the probe should be adjusted prior to use.Usually there is an adjustable capacitance at one end of the probe near the oscilloscope, and some probes are near
The probe also has an adjustable capacitance at one end.They are used to adjust the impedance matching of the oscilloscope probe.If the impedance does not match, the measured waveform will be distorted. The method of adjusting the impedance matching of oscilloscope probe is as follows: firstly, the input selection of oscilloscope is played on GND, and then the Y-axis displacement knob is adjusted to make the scan line appear in the middle of the oscilloscope. Check if the scan line is horizontal (i.e., if it coincides with the horizontal center line of the oscilloscope), if not, adjust the horizontal balance knob (usually the analog oscilloscope has this adjustment terminal, in the hole, need to use a screwdriver into the adjustment.Digital oscilloscope need not be adjusted).
Then, the input selection of the oscilloscope is connected to the dc coupling, and the oscilloscope probe is connected to the test signal output end of the oscilloscope (generally, the oscilloscope has this output terminal, usually the square wave signal of 1KHz), and then the scanning time knob is adjusted to make the waveform display for about 2 cycles. Adjust the Y-axis gain knob so that the peak - peak of the waveform is about 1/2 screen width.Then look at the top and bottom sides of the square wave to see if they are horizontal.If the phenomenon of overshoot and tilt occurs, it means that the matching capacitance on the probe needs to be adjusted.Adjust it with a small screwdriver until the waveform on both sides is level and there is no overshot.Of course, due to the quality of the oscilloscope probe, may not be adjusted completely without distortion effect, then can only be adjusted to the best effect.
High precision dither test of digital oscilloscope
Jitter can be described as the periodic change of edge period or phase of adjacent pulse edge or even non-adjacent pulse edge. These indicators are suitable for measuring long-term and short-term clock and data stability.The data transmission performance of complex system is predicted by analyzing the jitter index and using the jitter test results.
Periodic jitter is used to measure edge - to - edge timing of clock or data cycle samples. For example, by measuring the time between the rising edges of 1,000 clock cycles, you can sample the statistical cycles that will tell you the quality of the signal.The standard deviation becomes RMS periodic jitter, the maximum period minus the minimum period, to get peak to peak period jitter.The precision of each measurement period determines the precision of jitter measurement.
Phase jitter is used to measure the time deviation between the edge of the measured signal and the edge of a reference signal so that any change in the signal phase can be detected.This indicator is different from periodic measurement in many ways. First, it USES each edge alone, without saying "period" or "cycle."Second, it can measure large time shifts.The edge phase can be deviated by hundreds or thousands of degrees, but can still be measured with very high precision (360 degrees equals one cycle or cycle time). The commonly used measure of phase error is the time interval error (TIE), and the measurement results are expressed in seconds relative to degrees.TIE matches the signal edges to the reference edges, and sums up the differences between the edges.After comparing a large number of edges, a sample set can be provided for analysis.As with the above periodic measurements, the standard deviation becomes RMS TIE, the maximum time minus the minimum time to get peak to peak TIE and so on.