07_22_2010 IR drop / power structure study

Both GC and ISP have M7 on top, but you can't expect this all the time, it is a bonus and keep changing. M7 is just for vcc_block.

Both GC and ISP are in the switching power domain, this means they have always on and switching power. vcc_m1 ( always on ) and vcc_block.  The role of vcc_m1 is to supply the power to the always on power part and the power switch cell. vcc_m1 is relative straight forward. vcc_block is tricky.

GC, power distribution structure:

           M6, M4 vertical straps.  M6 strap width is 5um, M4 strap width is 0.4um.

           There are twice M4 straps than M6 straps. half of the M4 straps are in between M6 vcc_gc and vss straps. The structure is solid. M4 straps are connected to M1, M6 is connected to M4. For the in between M6 strap M4s, the power is solid. For the "floating" M4s, they connected to the power network through M1 ( what a shame ).

           For the macro region, M5 horizontal straps are added. Macro picked up the power through M4 pins, then M5 horizontal straps, then M6 the main power straps. The power is ok or solid for macro.

  note for GC: there is a weak spot for a small area between marcos. IR drop is big, reason, there are M4 straps but it is not connected to M6 directly, the connection is like this:  M4 picked up the power from M1 and distributed to other M1 ( stdcell ),  I guess Da Xia made some last minute fix, he extended M5 straps of Macro to connect these M4s.

ISP power structure:

          Three layer power network. M6 and M2 are vertical ones. M5 is the horizontal. It is a three layer power mesh. M2 is not needed to align with M6. It is a very solid three layer power network. No special treatment is needed for macros.

    note for ISP: need to make sure there are Power Switch cell in between macros ( both horizontally and vertically , Ki-Tae only guaranteed horizontal switch cells, I think the IR will be better with switch cells vertically in between macros ). need to make sure at least a pair of M2 straps in between macros.

So Jeffrey's power mesh

1. Three layers M2, M5, M6 
2. I will use less dense M6 then ISP to give back M6 routing resource.
3. Make sure the gap between macros is wide enough for one row of switch cell
4. Make sure the gap between macros is wide enough for one column of switch cell
5. Make sure the gap between macros is wide enough for one pair of M2 straps
6. Make sure the gap between cell and boundary is wide enough for power switch cell
7. Add vcc_block, vss ring around the block.