For my analog project, I am trying to figure out how to handle the clamp signals

io_clamp_low[0:2]

and

io_clamp_high[0:2]

. The image below sums up my understanding of esd protection. Is this accurate for caravel? If so, where do these two signals lie on the diagram?

The power clamps in sky130 are built into the power pads (both power and ground) and are left unconnected and have to be connected with an "overlay" cell. All power and ground pads in caravel and caravan are wired up to power clamps under the pads. The caravan chip is slightly different in that the three pads on top that have the clamp connections do not have an overlay cell, so the clamps are free-floating. The intent is that if you need a special power supply (e.g., a high-current-capacity supply), you can use one of those pads for the supply, and probably another one for the (presumably equally high-current-capacity) ground return, and you would want to add a clamp to it by tying one (or both) of the clamps under the pads between your power and ground. If your circuit on caravan makes use of the

vdda1

or

vdda2

supplies (or, for that matter, the

vccd1

or

vccd2

1.8V supplies), then they are already clamped. You are also free to tie any of the three floating clamps to any of the power rails (preferably the 3.3V ones, since they are high-voltage clamps), although that would leave no short path for clamp current between power and ground, due to the lack of access from the analog user area to the padframe power rings, so that's probably not a good idea. Because the connections have to extend into the user area, it's not a great setup for ESD all around, but it's better than no ESD protection.