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Published: Sunday, 12 July 2020 14:43

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DFT: Design for Testatbility

Any chip that is fabricated is going to have some defects during fabrication, which will cause some of the transistors or wires on the chip to not function properly. This may cause the chip to fail. One way to check if the chip manufactured is good or not, is to run thru the same functional patterns on the chip pins that the chip is going to go thru when it's in operation.

For small chips this method may work, but for large chips, it's practically not feasible for 2 reasons. First, there may be billions of such possible patterns on chip pins that we may have to aplly, which is time prohibitive. Secondly, it may still not find out all bad devices or bad connections in chip, since those patterns may not target 100% of the chip devices.

Without having 100% check to test each and every transistor and each and every connection, we can never be sure if the chip being shipped is 100% functional or not. This is where DFT comes. DFT simply means adding extra logic on chip so as to allow us to test the whole chip. DFT is a broad field by itself, an you will usually see thousands of job postings just for DFT engineers.

In this section, we will go thru the basics of DFT,