I/O layout in comparison with Analog layout???

[lohitha]

can anyone tell me some highlights about I/O layout in comparison with Analog layout???
As i have worked on analog layout design(floorpln, routng,verfctn,etc...)

 

[erikl]

Your main concern will change from fighting against mismatch to fighting against ESD & latchUp.

 

[dgnani]

Usually the dominating concern with I/O are very large currents to be dealt with in very small times. This requires very low access resistance to your devices and attention to current crowding effects. All devices dealing directly with ESD discharge path will be very large, split in several fingers and occasionally shaped to minimize edge effects (avoiding 90deg angles in metal and diffusion).
In addition latch up requirements will basically force you to isolate all these devices with single or double rings (following foundry dependent rules).
In some technologies there will be a significant weight in terms of annotation layers or labels required to identify the devices or even part of the devices that will be directly connected to the pad.
Other concerns come from the necessity of modularity (creation of rails by abutment) and mechanical toughness:
- large metal might have to be slotted or split
- there will be special rules for the region of the I/O under the bonding pads themselves (because of the mechanical pressure they will be subject to) with limited or no active devices allowed.
The layout of the bonding pads themselves require special rules usually well detailed by foundry manuals