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Guild: wafer.space Community
Channel: ℹ️ - Information / general / Using gf180mcu_ocd_io in LibreLane
After: 2025-11-30 11:59 p.m.
Before: 2026-01-01 12:00 a.m.
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[2025-12-04 9:02 p.m.] 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.


[2025-12-04 9:04 p.m.] 246tnt
Violating rule is `ANT.16_i_ANT.3`


[2025-12-04 9:05 p.m.] 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.


[2025-12-04 9:14 p.m.] 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
```


[2025-12-04 9:15 p.m.] 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


[2025-12-04 9:32 p.m.] 246tnt
Ah ... the DRC rule only consider `nplus + COMP` to be diodes.


[2025-12-04 9:32 p.m.] 246tnt
But the IO have `pplus + COMP`


[2025-12-04 9:44 p.m.] 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.


[2025-12-04 9:44 p.m.] 246tnt
(cc @Leo Moser (mole99) )


[2025-12-05 7:40 a.m.] 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?


[2025-12-05 7:51 a.m.] 246tnt
TBH I would think `comp.and(nplus.or(pplus)`  would be enough.


[2025-12-05 7:52 a.m.] 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.


[2025-12-05 7:53 a.m.] 246tnt
But it's a rather weird case so the above would work just fine.


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