the width of guardring

Hi,
To reudece the latch-up issue and to increae the isolation of the cross talk between the ditiatal and analog part. The dual guardring is put arounfd the ditital part. I want to know if the wider of the guardring, the better for the above two goals?Asume the die area is not a concern.

Thanks

chang830 said:

Hi,
To reudece the latch-up issue and to increae the isolation of the cross talk between the ditiatal and analog part. The dual guardring is put arounfd the ditital part. I want to know if the wider of the guardring, the better for the above two goals?Asume the die area is not a concern.

Thanks

Click to expand...

i think so.however,if u cannot measure it out.

chang830 said:

Hi,
To reudece the latch-up issue and to increae the isolation of the cross talk between the ditiatal and analog part. The dual guardring is put arounfd the ditital part. I want to know if the wider of the guardring, the better for the above two goals?Asume the die area is not a concern.

Thanks

Click to expand...

I don't think the wider the ring, the better for the mentioned problems. What is important is that the depth of the ring which is controlled by process.... well, maybe wider ring help a bit. But the depth of the ring is much more important.....

Big width of the guardring is helpful. But beyond some limit (e.g. 50um), further widening cannot increase more latch-up immunity.

HI ,
By incresing width of guardring latch-up immunity will increse , and isolation b/w digital & analog also increase but we can't measure how much isolation (if there is no area constraint we can keep more width).

By guardring I assume you mean P+ diff. connected to GND and N+diff connected to VDD. This way you will trap carriers what will help with latchup. Also good substrate contacting arround your devices is important.
For crosstalk between the digital and analog portions I would recommend space of min 50um (best would be space equal to thickness of the EPI), trench, deep Nwell or atleas nwell - which will create deeper barrier.
Wider guardring will not help much since you effectively short the area - high impedance is better for crosstalk

chang830 said:

Hi,
To reudece the latch-up issue and to increae the isolation of the cross talk between the ditiatal and analog part. The dual guardring is put arounfd the ditital part. I want to know if the wider of the guardring, the better for the above two goals?Asume the die area is not a concern.

Thanks

Click to expand...

Yes, I think so
But some time we will use different guard rings. N-well, P+, and P-well etc.
and the metal connected guard ring should be large enough.

I agree with one of the very first posts... Except on very particular cases, the width of the guard ring is not important, the most important thing would be to have it there and having the correct depth and functionality.

What I mean with this is that, usually, rings are there just to collect some noisy or undesired signal components, but minor ones, that's why (I said) it's not important the width (you shouldn't drive a lot of current there).

One particular case (as I mentioned before) would be a substrate contacts ring around an ESD protection structure, in that case I would yes recommend having a wider enough ring.