How to correctly ground a NMOS transistor?

[Shlapenka]

Hello everyone,

I am having this problem, connecting bulk connections to substrate. When its PMOS i have no problem, i make a Ntap in the same nwell as the PMOS is and connect it to VDD. When it comes to NMOS, i cant figure it out... I put a NMOS transistor, near it i put a Ptap and connect that Ptap to GND. And it seems that it is wrong! It says that the net is incomplete, i zoom the place of that incomplete net ant it shows that NMOS transistor. Everything elese is ok. So what am i doing wrong? Im using virtuoso. If it is not too much to ask maby someone could post a pic of correctly grounded NMOS transistor? Thank you so much!

 

[erikl]

Re: nmos grounding

... I put a NMOS transistor, near it i put a Ptap and connect that Ptap to GND. And it seems that it is wrong! It says that the net is incomplete, ...

Both the source of the NMOS and the Ptap must be connected to GND by metal1.

 

[standup]

Re: nmos grounding

... I put a NMOS transistor, near it i put a Ptap and connect that Ptap to GND. And it seems that it is wrong! It says that the net is incomplete, ...

Both the source of the NMOS and the Ptap must be connected to GND by metal1.

Not all the source of NMOS should be connected to ground. If you place a psub contact next to a NMOS cell, the LVS tool will recognize it as a NMOS device. The "incomplete net" error maybe for you don't connect all the contacts together

 

[alfredop]

nmos grounding

What technology are you using to implement your design?

If you are using a single-well CMOS process, like AMI's 0.5 um for example, individual PMOS devices can be built in separate n-wells but all NMOS devices go on the same p-well (the substrate). In such case, you don't create source-to-bulk connections for each individual NMOS transistor in your layout; instead, you tie the entire substrate to the lowest potential used in your design (VSS, or GND) using as many contacts (p-well contacts) as possible --make sure the bulk terminal of all NMOS transistors in your schematic is also connected to the lowest potential.

Hope this helps!

 

[Shlapenka]

Re: nmos grounding

hey alfredop,

thank you for very clear answer. yes i am using a gpdk090v4. now i clearly understand, +rep for everyone!