DVD - Lecture 3d: LEF

[@bhargavisetlem]

Nice explaintions sir.... Thank you 😊

[@AdiTeman]

Thank you!

[@hansyu1688]

Dear Dr Teman, your slide webpage is not loading, could you check it please. I really enjoy your teaching and I learned so much from your course.

[@AdiTeman]

I checked and it is working now. I'm not sure why you couldn't access it before.

[@analprakashsharma3026]

Its not opening now also.@@AdiTeman

[@nidhiupadhyay357]

Hi I want to know why we are using implant layer in OBS??

[@AdiTeman]

Hi, I'm not sure what you are asking - is it something from the slides I showed in my lecture or is this a question from something you have run into at your work? If it is from the slides, I probably got the image from something I found on the internet and can't vouch for the exact example. If it is something from "real life" then I can try and guess the following explanation. There is no 100% accurate standard or way to make library files and therefore you get different things from different vendors (and different products). Most of the time (yes, for almost every library or IP you get) there are things that don't exactly "fit" and you often need to "fidget" with them. This usually doesn't make it to the level of the design engineer, but is taken care of by the CAD team that makes sure that the entire flow works with the tools the company uses and the processes they are using. But believe me - there is a lot of adaptation of LEFs and LIBs from what you get from the foundry/vendor. With that, I can tell you that extra information is not detrimental; so you have OBS on an active layer - it's not going to do anything bad, just make the LEF file a few KB bigger. In a certain techfile, possibly the router could (strangely...) consider such a layer as a routing layer and then the LEF would need to add the diffusion as an obstruction. But this is not the standard way things are done, and it could lead to other not so nice consequences. But that may be the reason you see this...

[@HusnaRukhsar-f9t]

Can you explain why the tech lef file is required when we have tech file?

[@AdiTeman]

Yes. Basically these are from "two different worlds". The techfile is (traditionally) part of the PDK. In other words, it comes from the custom design (analog) world, used by programs, such as Virtuoso. The tech lef is for the backend (digital) world, used by programs, such as Innovus and ICC. There have been attempts by the various vendors to combine the two - this is basically what Cadence OA databases are doing (in at least one respect). But this hasn't been adopted too widely, so usually we provide a tech lef for the backend flow and a techfile for the circuit design flow.