basic questions in digital layout

I just started reading jan rabaey digital integrated book. Here my question is about digital layout.


I heard digital layout is mostly done by CAD tools. So i am wondering why we
have to study all the indepth deatils of basics from the book. I know that we need foundation in basics. Can't the CAD tools take care everything in the floor planning and layout stage.

-novice

Hi,

Prety good question as a bigner.. When I was in your place (near bout 6-7 year before) even I was thinking in the similar way.
Its very difficult to clearify this thing here becuase you are new in this field, you can come to know by experience that why reading is important. But still Let me try.

You are right that Most of the thing is done by the CAD tools.. But you urself use one thing "MOSTLY".. means there are lots of other things which CAD tools can't do. And the worst part is that as a designer you dnt know what rest you have to do yourself.So you should know every thing about the VLSI to solve that thing.

Another thing.. as we know that not a single tool(software ) is 100% error free, there are lots of bugs and lots of area of improvement. But in the chip designing you can't take a risk of even 1%. Because if it will happen then may be the Chip fitted in your laptop/mobile suddenly stop working and then you will complaint to the provider. So every design company have their internal test case to verigy the CAD tools and the team who is developing those test case should have understanding of every thing. Not only basic but they should be updated for this.

Similar things happen in the development center of CAD tools. If they dnt know about the VLSI properly then how will they develop those tools.

For designer team perspective... Some time because of some special specification/non avaliablity of any feature in the CAD tool , they have to debug a lot of things in the design and find out the root cause of problem and then has to solve them. For that they should have sound knowledge of VLSI.

So in short , I can say that 90% of the design can be done by CAD tools, but for a chip this 90% is not that important but rest 10% is important. So you wana be a VLSI engg then remember that you will work in the 10% of design , rest 90% anyone can do it. nad that's the reason you can see a lot of Computer Science student in VLSI domain, but those are in the CAD tool development not in the design side of Chip. (exception is every where).

Hope this will clerify your doubt.

Keep posted your question .....
Thanks-
Birdy-

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Yes Novice,

The CAD tools can take care of the algorithms and stuff like that. But each command for a tool will have several options...these options will make a difference how the tool perceives a task. At the end of the day a tool needs to be told what it must do...thats where we designers come to picture. To guide the tool and tell it in which manner it has to approach and which optimizations need to be performed on our design.
Another thing is, once the tool generates a report there will be several results which need tweaking, because there are bound to be violations. And for each violations there might be several ways of correcting.

So how can a designer take those decisions for the tool? Only when we know the intricacies of the technology we are working on and at the same time we need to know how the tool approaches each task. So your knowledge on the basics combined with the tool exposure will help you get the best out of your design.


I think it is pretty clear to you now...

Thank you birdy,phoenixpavan. Could you suggest some books for layout basics and also projects for learning. I want to put those projects in resume and try for job. Any help is really appreciated.

Novice

Hi Novice,

Rabaey is a very good book and you have already started it..so nice start.
Besides that, start going through CMOS VLSI by Weste..These two should serve your purpose. As a reference you may go through ASIC by Smith.

For projects, anything will be good enough..but understand the concepts behind each step you run through your design....in interviews you will be probed on why you have done a particular step rather than how you did it as you have several choices for performing a particular step. So the focus will be on why did make a particular choice and what was the outcome.

All the best.