The Power Delivery Network is what provides power for all the macros in your design.

For the shuttle, LibreLane creates a PDN that supplies the 4 rails available to the user project area:

inout vdda1,    // User area 1 3.3V supply
inout vdda2,    // User area 2 3.3V supply
inout vssa1,    // User area 1 analog ground
inout vssa2,    // User area 2 analog ground
inout vccd1,    // User area 1 1.8V supply
inout vccd2,    // User area 2 1.8v supply
inout vssd1,    // User area 1 digital ground
inout vssd2,    // User area 2 digital ground

Metal 4 is used for vertical lines that are cut for the macros, and Metal 5 routes over the top of everything. When the metal 5 lines pass over the macro, vias are dropped to connect the macro’s internal PDN to the user project area’s PDN.

A common failure for small designs with the LibreLane tools is that there isn’t enough area for the PDN to get created. A simple fix is setting the absolute size of the die to make sure its large enough.

Course feedback

This course has fundamentally changed how I will teach VLSI in the future. Having used and taught the closed source tools, I am now a convert to the open-source tool chain. This course was the guiding force to get over the initial hump of the learning curve near painlessly.

Devin (analog course)