What is a Power Delivery Network (PDN) in an ASIC?

The PDN is what provides power for all the macros in your design. It is a structured network of metal rails that carries supply voltages and ground to every cell across the chip.

How does LibreLane build the PDN for a Tiny Tapeout shuttle submission?

LibreLane creates a PDN that supplies the 4 rails available to the user project area — two 3.3V analog supplies, two analog grounds, two 1.8V digital supplies, and two digital grounds. Metal 4 is used for vertical lines and Metal 5 routes over everything, dropping vias to connect macros.

What is a common PDN failure with LibreLane for small designs?

A common failure for small designs is that the die area is not large enough for the PDN to be created. A simple fix is setting the absolute die size to ensure it is big enough.

PDN

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February 7, 2021

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.

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.

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The Zero to ASIC course was great! Through this course I became more proficient with Verilog and started to not just appreciate, but actually enjoy the design verification! It offers the glimpse at the superpower too - seeing the traces of the original design in what used to be just squiggly lines of the masks before. Plus, I am getting my own piece of a silicon 🙂

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