In caravel analog example, why those io_clamps are...
# sky130h
Hugo Dias
02/22/2022, 6:10 PMIn caravel analog example, why those io_clamps are "conected" to metal3-rmetal3-metal3 and connected to the vssa1? And what the importance of rmetal?
w
Weston Braun
02/22/2022, 6:14 PMRmetal is the easiest way to do a net-tie. As spice / magic can have issues when two ports are connected directly
Weston Braun
02/22/2022, 6:14 PMRmetal 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
02/22/2022, 6:15 PMHere it is used to connect the IO clamp to vssa while having it still be a separate net.
h
Hugo Dias
02/22/2022, 6:16 PMIf i dont use any analog pins with clamps, do i need to connect clamps on vssa?
w
Weston Braun
02/22/2022, 6:18 PMYou are using the caravan harness, right? A few of the analog pins are more designed as power pins and thus they have the clamps.
🌍 1
Weston Braun
02/22/2022, 6:19 PMI forgot the exact structure, this may be a question for @User . But you should be able to leave them floating.
Weston Braun
02/22/2022, 6:20 PMYou 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
h
Hugo Dias
02/22/2022, 6:25 PMIn 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?
t
Tim Edwards
02/22/2022, 6:33 PMvddTim Edwards
02/22/2022, 6:35 PMTo 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.
h
Hugo Dias
02/22/2022, 6:55 PMIf i use rmetal, it will change just the extraction? In real life, rmetalX=metalX?
t
Tim Edwards
02/22/2022, 6:57 PMYes, 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.
h
Hugo Dias
02/22/2022, 7:27 PMCan i let io_clamps floating (if i dont use them)? If dont, should i conect them on vssa like example?
t
Tim Edwards
02/23/2022, 2:40 PMYes, you can leave them floating.
2 Views