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Why Standard cell inputs tied with a NAC diode?

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santhosh.mandugula

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nac diode

Why Standard cell inputs tied with a NAC diode as shown in the figur? Why the input is tied down (diode connected in RB)?[/img]
 

antenna rule nac

It is often called antena diode - in general you do not want to have long or large pieces of metal comnected to your gate since during processing there will be a charge buildup on those metals.
To mitigate this the gate must be tied to the diffusion. Gate A is not and you have not idea how long the metal line to it will be - therefore the diode. Gate be is though connceted to gate A drain diff. and so no diode is needed.
Refer to Antenna rules in pdk documentation.
 

nac diodes

I know how a NAC works but how does a charge thats accumalated in a metal gets neutralized when it reaches the diffusion?? Kindly post any materials in this topic
 

when do u need a nac diode

In one of the pdfs that i went through to learn more about Antenna effect, it is mentioned that adding a nac would add to the capacitance on the net and increase leakage power. Can any1 explain how the above statement is justified??
 

gated nac diode

Srinath Nair said:
In one of the pdfs that i went through to learn more about Antenna effect, it is mentioned that adding a nac would add to the capacitance on the net and increase leakage power. Can any1 explain how the above statement is justified??
Click to expand...

hi.. can you upload the pdf to here
 

santhosh.mandugula said:
Why Standard cell inputs tied with a NAC diode as shown in the figur? Why the input is tied down (diode connected in RB)?[/img]
Click to expand...

during etching of metals, there is a possibility of charge build-up because of antenna effect. to reduce this effect, you have to put NAC diode so that the poly layer will not be burnt.
 

Srinath Nair said:
I know how a NAC works but how does a charge thats accumalated in a metal gets neutralized when it reaches the diffusion?? Kindly post any materials in this topic
Click to expand...

Hi Srinath

As far as i know, the NAC diode is nothing but a pn junction diode whose one end is connected to the gate and the other end is connected to gnd. The idea is same as an ESD diode wherein any extra charge accumulated on the gate would be shorted to gnd.
Any comments are welcome.

Regards
Brittoo
 

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