Some questions about body connection. please replay

Hi everybody
I have some questions and need your help:

1- why body connection is important? (I know one of the reasons. see q.3)

2- I have designed a simple circuit at schematic level. I have connected the bodies of
all mosfets to correct voltage level. I use LayoutXL in cadence to create the layout. it
uses pcells to do this, but the mosfets has no body connections. Why?

3- I know that the voltage difference between body and source affects the threshold
voltage of MOS. I have seen some layout examples in internet. I wonder
why there is no body connection for mosfets at these examples?

4- when we want to use an NMOS as a transmission gate , should we connect the
body to GND? (there would be voltage difference between source and body anyway) (I stopped at layout stage because I don't know the answer of this question!)



Thanks a lot

Hi a.akbari61

Latch up is one of the reason for substrate connection.
You can always get the substrate contacts after pcell is generated from properties.
In general we prefer having substrate ring for a group of transistors than having individual connections for every transistor. It saves lot of area.

Also we can enable option of getting body connection along with the pcell.
But I'm not sure where to do this.
Can any one explain where to change the setting inorder to get body connections while generating with layout XL??

Regards,
Sree

thanks sree_lakshmi

Could you please show me how to use substrate ring for a group of transistors ?
And what about q. 3 & 4?!

Best

in the image, for group of transistors a substrate ring is drawn on the top.
in this case it is covered on only one side, but you may cover it on 4 sides.
can you send me the link in which mosfets have got no back gate connection?

for 4th ques, to which net the transmission gates bulk is connected in the schematic?
i dont see any prob in connecting them to ground.