==============================================================
Guild: wafer.space Community
Channel: Information / general / Using gf180mcu_ocd_io in LibreLane
After: 11/30/2025 23:59
Before: 01/01/2026 00:00
==============================================================

[12/04/2025 21:02] 246tnt
Mmm, I'm having an antenna violations when connecting to the `SEL` signal of the `ocd` IO but I don't see how that would be possible.


[12/04/2025 21:04] 246tnt
Violating rule is `ANT.16_i_ANT.3`


[12/04/2025 21:05] 246tnt
But (1) the `Metal2` line that connects to that pin is really not that long, like 90 um or so. And (2) there is AFAICT an antenna diode on that input.


[12/04/2025 21:14] 246tnt
The detail on the error is :
```
ametal_eff: 202.5162
ratio: 401.817857143
agate: 0.504
max_ratio: 400
pmetal_factor: 0.54
adiodes: (0)
diode_factors: (800)
pmetal: 375.03
```


[12/04/2025 21:15] 246tnt
And indeed the gate area is 0.504.  But there is an 1 um x 1 um diode on the same node, so the effective area should be 0.504 + 2 * 1 = 2.504 and thus the ratio is 80 which is _way_ below the 400 threshold


[12/04/2025 21:32] 246tnt
Ah ... the DRC rule only consider `nplus + COMP` to be diodes.


[12/04/2025 21:32] 246tnt
But the IO have `pplus + COMP`


[12/04/2025 21:44] 246tnt
Looking at the doc : 
"""This comp area contained the protection diode and any other drain or source junction connected to this node."""

so `pplus + COMP` is perfectly valid and should be included in the `diodes` so I'm pretty sure that KLayout deck is wrong.


[12/04/2025 21:44] 246tnt
(cc @Leo Moser (mole99) )


[12/05/2025 07:40] mole99
Thanks @tnt for the hint!

From the DRM:

> 1. Possible repairs to metal antenna nodes, which have a high via count or antenna ratio.
>   a. Add an NCOMP/Substrate diode for NMOS gate, PCOMP/Nwell diode for PMOS gate.
>   b. Break the metal close to the gate and jog the metal to an upper metal level.

So instead of:

```
diode      = nplus.and(comp)
```

I would do:

```
n_diode    = nplus.and(comp).not(nwell)
p_diode    = pplus.and(comp).and(nwell)
diodes     = n_diode || n_diode
```

(deep nwell not considered.)

Does that look reasonable to you?


[12/05/2025 07:51] 246tnt
TBH I would think `comp.and(nplus.or(pplus)`  would be enough.


[12/05/2025 07:52] 246tnt
Technically if a signal is connected to what's basically a tap, that's also a diffusion that will dissipate charge I would think.


[12/05/2025 07:53] 246tnt
But it's a rather weird case so the above would work just fine.


==============================================================
Exported 13 message(s)
==============================================================