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How to check an oscilloscope without a graphic function
Knowledge Base + 2023.12.12

The function of nowadays oscillograph is more and more powerful, oscillograph just already did not see weaveform simply, a lot of clients want to survey a plan with oscillograph recently, but the budget is limited, at hand does not have high-end oscillograph (for example DPO7354C) , so how to survey a plan?

Want to understand above all, What is a graph.

     "The eye pursues even if resemble an eye the graph of same figure. " eye graph is the bit that accumulates overlay to show the serial signal that collects with twilight means result, the graphical figure after overlay looks and eye very picture, friend name eye pursues. What show normally on eye graph is the time window of 1.25UI. The appearance of the eye is various, the appearance that the eye pursues is various also. The appearance characteristic that pursues through the eye is OK the quality of apace judgement signal.

The bit that because eye graph is to use a piece of figure,complete the earth's surface collected serial signal information, it is the most important to became those who judge signal quality so tool, eye graph is measured accession cries " signal quality checks (Signal Quality Test, SQ Test) " . In addition, the outcome that eye graph measures is eligible unqualified still, its judge a basis is opposite normally at " pattern plate (Mask) " . Pattern plate provided serial signal " 1 " the tolerance of n, "0 " the tolerance of n, the tolerance of rise time, decay time. So eye graph is measured accession is called again " pattern plate checks (Mask Test) " .

The appearance of pattern plate is various also, normally if the pattern plate of NRZ signal pursues 5 with the graph place of 8 blue part is shown. The different node that be defeated is passed in serial data, the pattern plate that the eye pursues is different, should notice when choosing pattern plate so specific child pattern plate type. If use the pattern plate that sends end to regard sink eye as graph pattern plate, may touch pattern plate all the time. But the signal that resembles aether net signal, E1/T1, not be NRZ code form, its pattern plate is more special. Should have bit when coming up against pattern plate, we think signal quality is bad, need debugs circuit. Some products ask 100% cannot touch pattern plate, some products are the probability less than with allow to touch the frequency of pattern plate to be in certain.

Falling without the good case that faze and noise string together between the code, weaveform is not had lack fidelity, every code yuan be together jackknife, what see finally on oscillograph is trace fine clear " eye " , "Eye " open is gotten the biggest. Should have when faze is being strung together between the code, undee and lack fidelity, pile up yuan of not complete coincide, the trace that the eye pursues is met unsharpness, cause " eye " the part closes. Be like the influence plus noise, make the line of a graph becomes ambiguous, "Eye " open is gotten small, accordingly, "Eye " patulous size showed lack fidelity rate, mirrorred what faze strings together between the code is strong weak. From this knowable, eye graph strings together the influence of faze and noise between can intuitionistic upper plain code, can evaluate a base band to transmit the actor bad of systematic performance. The character that also can use this graph butt joint to receive filter additionally tries to adjust, faze and the transmission that improve a system are strung together in order to reduce between the code function.

WithOscillograph checks a graph to have 3 kinds of methods, will divide according to testing the effect and the requirement to oscillograph, following:

1, oscillograph contains a graph to measure a function.

Below this kind of circumstance, open a function directly, the instrument checks automatically, restore clock automatically and the test goes out stretch degree, shake wait for parameter, the effect is best, and it is mensurable test.

2, oscillograph does not take a graph to measure a function, the signal of the test includes data line and clock line.

Can use clock signal to regard as at this moment spark the eye graph that signal will come to to check data signal. This kind of method is very good also, can compare see eye logo state well and truly, the error is small, the operation is simple.

3, oscillograph does not take a graph to measure a function, signal has line of a data only.

This time cannot make a graph check, if must be measured also can qualitative test, the method is: Ascendant edge touchs use oscillograph signal, will spark the dot is migratory to cannot move till, spark oscillograph, open weaveform to maintain, the eye that can see signal roughly pursues, but the result is met preference, shake at least can slant small.

If at hand does not have high-end oscillograph, need to observe on oscillograph the eye pursues however, understand signal roughly circumstance, undertake simple measurement, so use peaceful overcomes DPO2000B, MSO2000B, MDO3000, DPO4000B, MSO4000B, on the economy such as MDO4000B series oscillograph, can realize a graph to measure through simple setting, Specific setting is as follows:

1, the signal that arrives with the observation when edge sparks;

2, the choice sparks means is litre / fall time, slope instead rises or fall;

3, will spark n of threshold value discretion adjusts the position that fit, best low cost is in 10% - 20% the left and right sides, high cost is in 80 - near 90 , will express to rise fall the threshold value limits that time sparks;

4, the basis is measured signal (estimation comes out) ascendant decay time about size, the choice sparks time is less than this time;

5, if the weaveform that sees after the setting is good pursues, do not have accumulative effect right now;

6, the function that opens Yu Hui, and increase undee brightness, can observation arrives to whether unusual signal happens;