understanding technology library files

[3wais]

I started to learn design compiler for a university project.

I'm supposed to use it with Nangate free cell 45nm library. However, I don't know anything about the library files. what they do, what they describe (the cells and attributes or whatever) . Is there anything I can learn that from ??

 

[hareeshravi]

Hi,
IC Fabrication requires use of pre-designed, tested and characterized set of gate designs. EDA tools convert our design to an implementable form by interconnecting the gate designs provided by the Fab. For e.g FAB1 may have 4 input OR (OR4) gate whereas FAB2 may not have a 4 input OR. If you are using FAB-2 library, the design tool will not use OR4. There are many more parameters like drive strength, Fan-in, Fan-out, e.t.c. which are crucial when selecting the gate. Each library element essentially contains Inputs/Outputs, Fan-in, Fan-out, delay, Cell Layout, parasitic R & C, e.t.c... Since cell characterization is required, the FABs have to roll out the libraries for each node.
So We give our design, tell the tool which library (collection of cells which we are using) to use and the tool does the selection. So if you are planning to give to FAB, be careful while selecting the libraries. If not, just glance through the library and understand many things.

 

[jrwebsterco]

What you are asking about is the "Liberty" modeling format, which is the ASCII source format that gets compiled into a binary DB file which is what Design Compiler (DC) uses for mapping a design to the final technology cells during synthesis.
Liberty files typically have a .lib extension, and DB files (as you already know) typically have a .db extension.

Synopsys separately sells its Library Compiler tool to compile a Liberty file into a DB file.
Synopsys used to own the Liberty format, but it was open-sourced years ago.

It seems likely that the Nangate distribution package included the .lib Liberty source files, and you could examine those in any text editor.
If you search for "liberty library cell" you will find links to the official open-source Liberty site and college lecture slides and so on, which should help introduce you to what all is going on.

BTW, most all cell libraries below 130nm are now using something called CCS (Composite Current Source) due to net-load versus cell-drive and other practical issues at the smaller technologies.
You might want to avoid the CCS concepts initially, to not get distracted with how complicated they can be.
NLDM (Non-Linear Delay Models) is the term used for the original approach, and is easier to get started with.
Note that CCS libraries (which is what you surely are getting for 45nm) sometimes also have the NLDM tables included them as well, so that humans can more easily follow trends as a helpful reference.