Oscilloscope can only measure waveform - the pattern is small

author ： Mr. Yibo hi tech, member of we media David

Under the traditional cognition , The main function of oscilloscope is to test an input waveform , Play a passive input waveform and measure it to show us . If you really think so , The pattern may be too small ！
 
I think you already know that , Mr. Gao's team has a high-end oscilloscope this year , The bandwidth reaches 59G, Specially designed to correspond to the design verification of customers and our own high-speed signals . Since this artifact , Many customers come here with their high-speed board , We hope to solve the problem of various high-speed signals through our artifact .
 
one day , We have an old customer who has cooperated for many years and brought their high-speed communication board to our laboratory , I hope we can help do some testing and guidance ！ What the customer needs to test this time is QSFP28 The optical module of , The rate is at 25Gbps about , from PHY Chip to optical module link . You know that , Since last year, Mr. Gao has been committed to developing general fixtures of various standards , It includes different kinds of optical module fixtures , This time we'll use QSFP Of HCB Fixture to test the customer's host a main board , hold PHY The signal from the chip goes through PCB Link to optical module , Then lead it into our fixture , Finally, check the eye diagram when it is connected to our oscilloscope through our coaxial connector .

After we connect the clamp and oscilloscope port , We can select the test suite in the software configuration of the oscilloscope , The interface is like this , The suite specifies the protocol we choose , Contains the specified code type , Hardware connection mode and other test contents .

Then set it step by step according to the setting steps , You can start testing ！ The first test ,PHY There are no weighting and equalization parameters on the chip , At this time, we can see that the eye diagram we tested is very small , There is no margin .

When we open the automatically generated test report, we can see , The eye height of this eye map is really small , Not meeting the requirements of the agreement .

At this time, do you feel that the function of the oscilloscope is only here , Then we have to do it manually PHY The chip is configured with different weighting and equalization parameters , Then constantly try various configurations to find an eye diagram that can meet the requirements ？
 
Yes , Generally speaking , As a hardware debugger , Indeed, they can only constantly try to increase the equilibrium parameters in this way , In general 3 individual tap Take the tap of , Every tap The value of is about 16 To 24 Kind of , In that case, try , In theory, the highest possibility is to try 24*24*24 So many combinations can find the best configuration , It feels like an impossible task .
 
At this time, we return to what we said earlier , Do you think the oscilloscope is really just for passive testing ？ If I told you , The oscilloscope can also automatically help us to select the best weighting and equalization configuration. Do you believe it ？ It's great to help us screen , The key is still automatic , It's just ！
 
Yes , Our oscilloscope can really do , We can start with this PHY The tap number of the chip is input into our oscilloscope , Then there is a function on the oscilloscope that can automatically adjust the input tap , The software automatically calculates an optimal configuration parameter , It looks like this ！

Then we can regress and convert to... According to this set of parameters of the software PHY Chip configuration , That is, according to this set of parameters in PHY Chip configuration , At this time, we will conduct eye chart test , The result is a very obvious optimization effect ！

In other words, the oscilloscope successfully helped us choose PHY The optimal weighting and equalization parameters of the chip ！