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Liquan Fang (promotion date: 28 may 2003)

System level testing of embedded analogue cores in SOC


Promotion date: 28 May 2003

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I tested the integrated circuit by applying the special test input signals to the circuit under test and comparing the output signals to the expected signals. If they match, that means that the circuit under test is good; if it doesn’t there are some defects or faults.

To develop a methodology to select the special test input signals means developing testing patterns. For a small circuit that is not too difficult, but for complicated chips, for instance SoC (System-on-a-Chip), it is very difficult indeed.

Could you tell us something about your research?
I tested the integrated circuit by applying the special test input signals to the circuit under test and comparing the output signals to the expected signals. If they match, that means that the circuit under test is good; if it doesn’t there are some defects or faults.

To develop a methodology to select the special test input signals means developing testing patterns. For a small circuit that is not too difficult, but for complicated chips, for instance SoC (System-on-a-Chip), it is very difficult indeed. So we divide up the chip into small blocks, which are called cores in SoC. At the first step we generate the test patterns for those relatively small cores. That is what we call the hierarchy strategy. Then I had to find out how to translate the signals to the system level. This is quite a new way of testing. Only two groups are working on this world wide: out group and the other one is in the United States. They also adhere to the hierarchy approach, but the translation of the different layers is different.

Did work together with this other group

No, there was no direct collaboration, but we met in conferences. There is a bit of a competition between the two groups; when they publish a paper we carefully look at what they are doing and I know that they are very eager to know what we are doing.

On some points we are ahead: some test patterns cannot be translated to the system level and we provided an extra strategy for test access. We are the first with this architecture.

So chip manufacturing companies would welcome you with open arms?

Yes, that is exactly why I already have this job with Philips. There are not many job opportunities when you are in semiconductors, but I have been lucky.

I had some network contacts because I had a 4 months internship with Philips during which I solved some problems for them. So they know I am of use in that respect. One year on probation and then I get a permanent contract.

Where are you from?

I am from eastern part of China. I had my education there and after that I went to Singapore to research in wireless communication. I worked with chips of course and I was curious how little thing like that could have such a complicated function.

So I looked on the internet for a PhD study I could do on this particular subject, and applied for the position at MESA+.

Are you never homesick?

No not really. My wife also works at the university here and we go for a visit to China every on or two years.

What did you like best about your study?

Before I came here, I only knew a little of the Netherlands. Everybody knows about the United States from Hollywood movies, but I had hardly any information about the Netherlands. The same applied to my friends in Singapore, they thought I was crazy to go to the Netherlands. We all expected a basically agricultural society, with cows and tulips. So I was in for a surprise. And I like the openness and friendliness of the people.

And about my research: I look forward to my promotion (12 June 2003). I published some papers, but they only deal with part of the problem. The PhD is the ultimate reward of the work.

What was the most difficult thing?

In my case a problem was that we did not get much support from industry. It would have worked much more efficiently if there had been less secrecy. Only when you become part of the company are they willing to reveal that there are in fact problems that need to be solved.

Are you still in research a Philips?

Well, at the moment I am working for production. But in the near future I will work partially for production and partially for research.

It is very different working in a company if you compare it with university work. In a company you have to carefully plan and then stick to your planning. You have less freedom, for when you change something it effects the work of others as well.

But I like it.

For the summary of the thesis, click here. (English)