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power routing for pads

gops
I intend to use0.18um TSMC library .When i choose the IO library i came to see that each IO cell need two VDD supply voltages one VDD(1.8V) and another VDDPST(3.3V). Also i found the VDDPAD and VSSPAD are provided for both core and IOs. I dont understand why we need VDD pad for IOs. Can anybody please tell me the reason in detail. Also please tell me reagrding power routing for IO cells.
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  •  I'm not sure I completely understand, and I'm not familiar with that particular library, but in general, there is a core VDD and an IO VDD. The core VDD I'm sure you're familiar with, and core-VDD IO cells feed the core grid. The power source coming into the chip connects to the pads of these IOs. The IO VDD is usually a ring that is connected by the IO cells abutting each other. These need a source from off-chip as well, which would be the pads of the io-VDD IO cells.

    Hope that makes sense,

     - Kari

Reply

  •  I'm not sure I completely understand, and I'm not familiar with that particular library, but in general, there is a core VDD and an IO VDD. The core VDD I'm sure you're familiar with, and core-VDD IO cells feed the core grid. The power source coming into the chip connects to the pads of these IOs. The IO VDD is usually a ring that is connected by the IO cells abutting each other. These need a source from off-chip as well, which would be the pads of the io-VDD IO cells.

    Hope that makes sense,

     - Kari

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