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I once met a person who told me as a part of his work he was testing and characterizing analog chips which include all sorts of components like ADCs, DACs, regulators ect. embedded in one chip. But he said he doesn't know how to design such a chip not at all about VLSI design.

How come such complex transistor level circuit functionality is understood by a person who wants to test it? Do they provide extra diagrams? And lets say if one wants to check only the ADC components how is that possible in such a complex system?

floppy380
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    Do you need to to know how a car engine, transmission, or suspension works in order to determine how it behaves when driving it? – DKNguyen May 19 '20 at 23:49
  • Yes thats my point but there must be some sort of diágram to be provided to the person who drive it instead of the transistor level schematics. What is such an easy to read diagram called in that discipline? – floppy380 May 19 '20 at 23:52
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    That's not what you actually asked – Scott Seidman May 19 '20 at 23:59
  • Even the people on the chip design team don't know how it all works, unless it is a very simple chip. – Justin May 20 '20 at 15:28
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    Video game testers don't know how to program the game - they just have to play it and make sure it works. Food testers don't need to know how to cook - they just have to eat and decide how it tastes. Sound testers don't need to design and build amplifiers or speakers, they just need to connect them and test that sound is produced correctly. Testers, generally, don't need to know anything about the internal design or implementation details of whatever it is that they're testing. All they need to do is to be able to follow a testing procedure and record the results. – J... May 20 '20 at 16:32
  • @J... They need to know enough to be able to *design* a testing procedure and ensure that the results aren't worthless, but actually applicable to the test goal. – Bergi May 20 '20 at 19:01
  • @Bergi Unless you're a startup, the people designing the tests will almost certainly not be the people carrying them out. – J... May 20 '20 at 19:21

1 Answers1

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All chips, from the very simple to insanely complex, have functional specifications. These describe what the chip does. The IC designer will make a circuit to implement that functional spec, while a validation engineer or test engineer will develop a set of tests to check the implemented chip against the same functional spec.

It's not necessary for a test engineer or validation person to know 'what's inside'. In fact, good practice avoids having these folks know the implementation details, lest any design assumptions creep into their tests.

In some very limited circumstances a test engineer may need to know a low-level detail, such as an I/O pad structure, to test it properly. They may also need to know about a larger block, like an A/D or D/A converter, in order to access its design-for-test capabilities. But otherwise they treat the chip as if it were a black box.

hacktastical
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  • So the term is called " functional spec"? Is there any electronics filed once learns how to read such a functional spec? Is that a diagramlike spec? Sorry for the ignorant question. Im planning to learn how to interpret such spec. – floppy380 May 20 '20 at 00:19
  • A functional spec describes the chip architecture, its I/O structure, its programmer's model (if applicable), its electrical characteristics and other details relating to how the device is used in a system. This spec is the source material that also produces the data sheet, programmer's guide and other reference materials. – hacktastical May 20 '20 at 00:24
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    Datasheets are a good place to start reading. Look at some datasheets for simple voltage regulators like the 7805 and the 317. They describe the functionality of the IC, what the key parameters are, and how they're tested. Often there will be block diagrams. – Adam Haun May 20 '20 at 01:29
  • For a simple device the data sheet *is* the functional spec. For anything more complex, there will be internal documentation describing functions in more detail that may not be included in customer-facing docs (for example, a complex IP block licensed from a third party.) – hacktastical May 20 '20 at 01:36
  • Regarding the "functional spec". is it the "Block Diagram" in Figure 1 here??: http://ee-classes.usc.edu/ee459/library/datasheets/LM7805.pdf – floppy380 May 20 '20 at 02:14
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    Everything *but* the block diagram describes that device as a functional spec. The block diagram is a hint at the theory of operation of the device, that is, *how it works* as opposed to *what it does*. – hacktastical May 20 '20 at 02:17
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    @floppy380 The functional spec is everything from page 3 to page 21. Pages 22 to 26 describe test configurations you can use to verify the functional spec (everything described in the tables). Page 27 is the mechanical spec. I would note though that reading documents such as this is not taught at college or really anywhere else to my knowledge. It's a skill you're supposed to develop on the job (I usually joke that they expect me to learn by osmosis). There are some youtube videos by good electronics engineers that show you how to read datasheets. I didn't have youtube when I started – slebetman May 20 '20 at 09:46
  • @AdamHaun It's not that hard to find datasheets of the 7805 and 317 that actually include full schematics. I've even seen datasheets of contemporary chips that include die photomicrographs, though I don't think I've seen that on a 78xx or 317. Might not be the best example to show someone the idea of working with *just* a functional spec. – Hearth May 20 '20 at 17:11
  • @Hearth, in the early days of ICs that was true, and the 7805 and LM317 date from that era. They basically were documenting what they built, and appended a set of characteristics and called it good. But that schematic isn’t a functional spec that a test engineer or a system designer would use. It’s a theory of operation, at best. – hacktastical May 20 '20 at 17:18
  • @hacktastical That's exactly my point. – Hearth May 20 '20 at 18:13