Author: Huang Gang, a member of Yibo Technology Expressway Media
In traditional cognition, the main function of an oscilloscope is to test an input waveform, play the role of a passive input waveform and measure and show it to us. If you really think so, your pattern may be too small!
I believe everyone already knows that Mr. Gaosuo’s team has a very high-end oscilloscope this year, with a bandwidth of 59G, which is specially used for the design verification of high-speed signals for customers and ourselves. Since we have this artifact, many customers have come here with their developed high-speed boards, hoping to solve various high-speed signal problems with our artifact.
One day, an old customer who has cooperated with us for many years came to our laboratory with one of their high-speed communication boards, hoping that we could help with some tests and guidance! This time, the customer needs to test the QSFP28 optical module with a rate of about 25Gbps, the link from the PHY chip to the optical module. As you all know, Mr. Gaosuo has been committed to the research and development of various standard universal fixtures since last year, including different types of optical module fixtures. This time we used the QSFP HCB fixture to test the customer's host motherboard, and the signal from the PHY chip was transmitted to the optical module through the PCB link, and then led to our fixture, and finally connected to our oscilloscope through our coaxial connector to view the eye diagram.
After we connect the fixture and the oscilloscope port, we can select the test suite in the oscilloscope software configuration. The interface is as follows. The suite specifies the protocol we choose, including the specified code type, hardware connection method and other test contents.
Then, after setting up step by step according to the setup steps, you can start testing! In the first test, no emphasis equalization parameters are turned on on the PHY chip. At this time, we can see that the eye diagram we tested is very small and there is no margin.
When we open the automatically generated test report, we can see that the eye height of this eye diagram is indeed very small and does not meet the requirements of the protocol.
At this point, do you feel that the function of the oscilloscope is limited to this, and then you have to manually configure different emphasis and equalization parameters for the PHY chip, and then keep trying various configurations to find an eye diagram that meets the requirements?
Yes, generally speaking, as hardware debuggers, they can only use this method to keep trying emphasis and equalization parameters. For example, for the taps of the usual 3 taps, there are about 16 to 24 values for each tap. In this case, if you want to try, theoretically you may have to try 24*24*24 combinations to find the best configuration. This feels like an impossible task.
At this time, we are back to what we said before. Do you think that the oscilloscope can only test passively? If I tell you that the oscilloscope can also automatically help us to select the best emphasis and equalization configuration, do you believe it? It is already very powerful to help us select, and the key is that it can be automatic, which is simply amazing!
Yes, our oscilloscope can really do it. We can first input the number of taps of this PHY chip into our oscilloscope, and then there is a function on the oscilloscope that can automatically adjust the input taps. The software automatically calculates the best configuration parameters, just like below!
Then we can regress and convert to the configuration of the PHY chip according to this set of software parameters, that is, configure the PHY chip according to this set of parameters. At this time, we will perform eye diagram test, and the result will have a very obvious optimization effect!
This means that the oscilloscope successfully helped us select the best emphasis and equalization parameters for the PHY chip!
提升卡
变色卡
千斤顶
京公网安备 11010802033920号
