Signal integrity testing means there are a lot of, some of the main means to have a waveform testing, eye diagram test, jitter test, etc., the signal integrity testing method is applied more widely should be waveform test, namely, using the oscilloscope test waveform amplitude, edge and burr, etc., through the test of waveform parameters, amplitude, the edge of time as you can see whether meet the requirements of the device interface level, is there such as signal burr.
The testing methods of signal integrity can be divided into three categories. Some explanations of these methods are given below.
Jitter test
Jitter testing is getting more and more attention now, because special jitter testing instruments, such as TIA (time interval analyzer) and SIA3000, are very expensive and rarely used. The most used is oscilloscope plus software processing, such as TEK's TDSJIT3 software. The software processes the components, such as RJ and DJ, and the components in DJ. For this test, the selected oscilloscope, long storage and high speed sampling are necessary conditions, such as memory more than 2M and a sampling rate of 20GSa/s. So far, however, the results of jitter testing vary considerably from company to company, and no one is an authority or industry standard.
Waveform test
The first requirement is that the host and probe together constitute enough bandwidth. Basically, the bandwidth of the test system is more than 3 times the bandwidth of the test signal. In practice, some engineers randomly find some probes to test, or even plug the probe of Company A into the oscilloscope of Company B, which makes it difficult to get accurate results.
Waveform test is the most commonly used means in signal integrity test, which is generally carried out by using oscilloscope, mainly to test waveform amplitude, edge and burr, etc. Through the parameters of waveform test, it can be seen whether amplitude and edge time meet the requirements of interface level of devices and whether there is signal burr, etc. Since the oscilloscope is a very general instrument, almost all hardware engineers can use it, but it does not mean that everyone can use it well. Waveform testing should also follow some requirements in order to get an accurate signal.
Second, pay attention to detail. For example, the test point is usually placed on the pin of the receiving device. If the condition limit cannot be placed on the pin, such as the BGA encapsulated device, it can be placed on the PCB routing line or hole closest to the pin. Too far away from the pins of the receiving device, because of signal reflection, the test results may be quite different from the actual signals. The ground wire of the probe should be as short as possible.
Finally, you need to pay attention to the matching. This is mainly for the use of coaxial cable to test the situation, coaxial directly connected to the oscilloscope, the load is usually 50 ohms, and dc coupling, and for some circuits, dc bias, directly connected to the test system will affect the working state of the circuit, so the test cannot be normal waveform.
Eye diagram test
Eye chart test is a common test method, especially for interfaces with specification requirements, such as E1 / T1, USB, 10/100base-T, and optical interface. Eye map testing of these standard interface signals is mainly performed with MASK oscilloscopes, including universal oscilloscopes, sampling oscilloscopes, or signal analyzers. These oscilloscopes have built-in clock extraction function to display the eye map, and for oscilloscopes without a MASK, an external clock can be used for triggering. Use eye diagram test function, need to pay attention to the number of test waveforms, especially for judging interface eye diagram is in line with the specifications, quantity too little, a shaking of the waveform is small, it may be a violation, such as the waveform into a certain part of the MASK, may collect less than, error by, the number is too much, will cause the entire test time is too long, efficiency is not high, usually, the test waveform amount not less than 2000, around 3000 as appropriate.
With the analysis software, you can view the details of the irregularities in the eye chart. For example, in the MASK, some sample points were dropped which were unknown before, because all the sample points are added up, the total effect looks like the long afterglow display. The new instrument, taking advantage of its long storage, collects the waveform and displays it, so every detail of the waveform can be retained. Therefore, it can check the irregularities of the waveform, such as whether the waveform is 000010 or 101010. This function can help the hardware engineer to find the root of the problem.
