In caravel analog example why those io clamps are conected t

Question

In caravel analog example why those io clamps are conected to metal3 rmetal3 metal3 and connected to the vssa1 And what the importance of rmetal

Weston Braun · Answer

Rmetal is the easiest way to do a net tie As spice magic can have issues when two ports are connected directly

Weston Braun · Answer

Rmetal for any given layer is the same material as metal but it is extracted as a resistor so the two sides are on different nets

Weston Braun · Answer

Here it is used to connect the IO clamp to vssa while having it still be a separate net

Hugo Dias · Answer

If i dont use any analog pins with clamps do i need to connect clamps on vssa

Weston Braun · Answer

You are using the caravan harness right A few of the analog pins are more designed as power pins and thus they have the clamps

Weston Braun · Answer

I forgot the exact structure this may be a question for < U016EM8L91B> But you should be able to leave them floating

Weston Braun · Answer

You also probably want some ESD protection structure though This analog pins don t have any protection beyond the clamp And even then I don t think the clamp is suitable for all cases

Hugo Dias · Answer

In my case i have 4 pins in digital vdd power vss ground out analog of GHz values I think i dont neet those analog pins with clamps or am i wrong

Tim Edwards · Answer

`vdd` should be connected to a clamp unless you are getting it from one of the standard supplies on Caravel Caravan vdda1 or vdda2 if it s 3 3V or vccd1 or vccd2 if it s 1 8V

Tim Edwards · Answer

To get GHz output you may want to forego ESD protection on the output line but then your chip will be extremely ESD sensitive Anything you can add reverse biased diode series resistance that you can get away without compromising your bandwidth will be helpful

Hugo Dias · Answer

If i use rmetal it will change just the extraction In real life rmetalX=metalX

Tim Edwards · Answer

Yes rmetal is the same as metal except that it will break the metal line into two different nets in the extracted netlist connected by a resistor When doing LVS you will need to represent the metal resistor as a device in the schematic netlist

Hugo Dias · Answer

Can i let io clamps floating if i dont use them If dont should i conect them on vssa like example

Tim Edwards · Answer

Yes you can leave them floating