needed brief explanation of attena effect

[mithri]

hi,

to reduce the atenna effect ,we place a higher order metal b/w the long interconnect and short gate.

the other way is to connect reverse biased diode ,can anyone explain how that diode reduces attena effect clearly.

thanks in advance

 

[varma_cs012]

It's just bypassing the charge accumulated over gate to ground through the reverse biased diode. It's one of the technique that we use to clean atenna issues.

 

[k_90]

In the fabrication process a charge will build on the diode until it switches on at 0.7 volts, then the diode switches on and discharges to ground. Thus eliminated the issue.

 

[mithri]

is it zener diode used there r normal diode.

 

[sridhar540]

IT IS ANTENNA NOT ATTENA

 

[sahmednc0]

is it zener diode used there r normal diode.

Hi Mithir,

I just signed up on edaboard recently. So, I didn't see your posting until today. You have seen replies already. But I thought I would give you my input too.

To handle the charge buildup in the lower level metals, as you already know you can jump to higher level metals. But you can also use a reversed biased diode. If you look at the I-V characterstics of a regular PN diode, you will see if it is reverse biased, very little (negligible) current flows but in forward biased, current flows with very little resistance. So, the built up charge can create a high positive voltage on metal line. But if you put a diode, this metal line becomes it's N terminal of the diode. And the P is the substrate which is grounded. So, by placing a diode in this fashion you create a reverse bias PN junction.

Zener diode works differently in reverse biased - it has a breakdown voltage..after which there is a large current flow. So, that's why you would not use a zener diode.

I hope that helps.

S.

 

[layoutmaster]

Hi to all,
I agree with all of you, but there's something else and really important to consider...
The reverse biased (almost negligible) current, as stated by sahmednc0 is not THAT negligible if you have, for instance, high temp conditions... in that cases you´ll have a leakage current that, depending on the circuit, could kill you...
Second, you must consider that most (I would say ALL) antenna effect checks are based on AREA RATIOS that show you lines or connections with "potential" antenna effect.
So, watch out and carefully study each case...because many times is better not to put anything...

 

[sahmednc0]

You are right. Even if you put a reverse biased diode, antenna problem might not go away. By placing diode, the ratio threshold is increased - which might still necessitate re-routing the net or jumping to higher level metal.

 

[Fom]

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