How to enable antenna DRC on Cadence?

[lbh00]

Hello all,

I got few questions concerning antenna design rules....
the problem that i have is that Diva rules that i have do not check for antenna errors and i see on Cadence site that Diva does support antenna checking through the command drcAntenna, but I am not sure how can i enable it for my designs?
is it through the .rul files ? can anyone give me a working example?

In addition to that I am not sure i do understand the antenna problem.... I asked colleagues around and they said all u have to do is to chop the long metal connected to the gate and bridge both parts with an upper layer metal.... If the problem is due to Ion etching and the accumulation of charges on the large piece of metal, then how bridging the two pieces with another metal prevents the accumulation of the charges on both metals now? aren't the two metals connected with vias which should conduct and hence let the charges also accumulate on all the pieces of metal ?
I am sure i am missing something over here but i dunno what can someone pls clarify this point for me ?

thanks in advance
lbh00

 

[Japp]

drc for anntena

Regarding your second question; Yes, the etching of long metal lines accumulate large charges on the metal, and when it has no discharge path it might break down the gate oxide.
So if you intend to use a long metal1 line connected to the gate then this will accumulate charges. If you instead make a bridge (i.e. cut this metal1 line close to the gate and use a via to go up to metal2 and down again on the next metal1 line) then the metal1 connected to the gate is only a small piece of metal that won't accumulate enough charge to ruin the gate oxide. In the next step when the metal2 bridge is made this small strap of metal2 is also so short that it won't accumulate enough charges to ruin the gate.
A rule of thumb is that the surface of the metal should not exceed the surface of the gate by more than a factor of 100 (this is of course dependant on the process and is found in the design rules)

 

[lbh00]

cadence diva gate antenna rules

This is correct, but the charges that accumulates on the small piece of Metal 2 are free moving charges so electrically the small piece of Metal 2 is actually the large piece of metal1 + the small piece of metal that is connected to the gate and hence we are back to a large area that accumulates the charges and connects to a gate .... what is wrong with this reasoning ?
I have read in the book "The art of Analog layout" by Alan Hastings that we move up to another metal hoping that the upper layer metal is connected somewhere to a diffusion which will leak the charges that builds up during the process.... Please comment on this....


lbh00

 

[cadenceguy]

metal bridge antenna drc

I've been doing layout 24 years..

1)The best way to resolve the antennae problem is to add a p-diode over nwell
or a n-diode over psub on the metal1 node that attaches to the gate.
The idea is that the diode will break-down before the gate-oxide.
This is an absolute on gates tied to bond-pads. The exception being in hi-voltage
circuits where you must be VERY careful about breakdown voltages.

2) Diva has a limitation on how many times a node transitions between levels
of interconnect before it gets "lost".
I recommend a stand alone ANT.rul file.. but there is a limit to transitions. ;')

3) Hack an antenna file from another technology.

 

[lbh00]

antenna rule diva

yes diodes are good solutions but what if I got to test these transistors at low gate voltages (0.2-0.3 V)then the diodes will disturb my tests....

I will try to h@ck a file from another techno and c what happens....

thanks for all of u guys ur reply were very informative

lbh00

 

[MohEllayali]

Re: antenna DRC

hi lbh00
i am facing the same reasoning issue, why jumpers solve antenna problem ???
have you got an explanation for that
hoping that there is a leakage path from an upper metal layer to ground is kinda tinkering relying on chance ?!:?:

 

[erikl]

Re: antenna DRC

... why jumpers solve antenna problem ???
have you got an explanation for that
hoping that there is a leakage path from an upper metal layer to ground is kinda tinkering relying on chance ?!:?:

See these topics:

#1287861

 

[MohEllayali]

Re: antenna DRC

... why jumpers solve antenna problem ???
have you got an explanation for that
hoping that there is a leakage path from an upper metal layer to ground is kinda tinkering relying on chance ?!:?:

See these topics:

#1287861

Thanks a lot erikl

 

[nsccad]

antenna DRC

lbh00,

PM me, i will try the Diva rule for you.