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[help] large transistor layout design.

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evilguy

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hi. i'm still new in analog layout design. i'm doing mixer double balanced mixer layout. i have read about using common centorid and multi-fingers transistor layout. i have very large width for my transistor. the W/l for one of my transistor is 2400/6 (lambda base). i have decided to devide the width using 60 fingers. is my method is true? below is my layout after splitting it into 60 fingers. please give any comment or suggestion to help me develop my skill in analog layout. thanks


edit: i have enter the complete layout that have all the transistor terminal including gate, drain, source and bulk.
 

papertiger

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1, the ploy contact is not centered. It is best to put more contacts.
2,I don't see the substrate contacts.
3, wider metal wire for big transister.
 

evilguy

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sorry. forgot to put the substrate. actually i still learning the correct geometry for wider transistor. can u eleborate more when you said my poly contact are not centered? how about the ploy? should connect all the poly using metal1 or using poly? how to make wider transistor as square as posible?
 

layout_designer

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Use metal as far as possible to connect gates becoz poly has higher resistivity compared to metal.

check what is amount of current that is passing and accordingly place more vias.
 

manissri

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u can use iron waffle method for large transistor layout.
regards
manish
 

evilguy

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papertiger said:
1, the ploy contact is not centered. It is best to put more contacts.
2,I don't see the substrate contacts.
3, wider metal wire for big transister.
so from your suggestion i understand that instead of using only one poly contact to connet metal, i have to use multiple contact similar like we use multiple contact at active area. am i right?
 

Son

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Multifingering looks ok. Use metal for wiring as far as it's possible. The poly gate doesn't need multiple contacts. For drain and source metallization, follow electromigration rules.
 

evilguy

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how can we make multi-finger transistor layout look as square as posible? or it is ok if the transistor layout is not square. how to draw the bulk terminal? i have draw it on the left ( refer to my update picture above). is it ok? i really appreciate if somebody can give me some example (note, paper or anything) on how to draw large Width transistor layout as a guide for me. thank you.
 

Hughes

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evilguy said:
how can we make multi-finger transistor layout look as square as posible? or it is ok if the transistor layout is not square. how to draw the bulk terminal? i have draw it on the left ( refer to my update picture above). is it ok? i really appreciate if somebody can give me some example (note, paper or anything) on how to draw large Width transistor layout as a guide for me. thank you.
It needn't be square.
As my opinion, the bulk terminal should be a ring surrounding the transistor to prevent latuch-up, since the drain current will be large.
 

ambreesh

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Kindly do gate wrapping also i.e. have contacts on both sides of the gate and short them. This helps in the rediction of gate resistsnce from noise perspective and also uniform application of gate voltage throughout the active gate length
 

evilguy

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Hughes said:
As my opinion, the bulk terminal should be a ring surrounding the transistor to prevent latuch-up, since the drain current will be large.
u mean i have to draw bulk like this (refer to my attachment) but i dont really understand about p+,substrate bias n+,Well bias and Block pin. What are those?
 

layout_designer

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how can we make multi-finger transistor layout look as square as posible? or it is ok if the transistor layout is not square.



Making it square increases routing complexity and routing parasitics. u got to keep parasitics in view.

Added after 28 minutes:

First think why we put sustrate contacts? what are the layers in the substrate contacts?

Then why these rings.

1.when considering for latchup both minority electrons and holes need to have discharge path. (becoz these can trigger latchup) hence the two substrate rings (guard rings).
2.Since for every "a"um u need to place substrate contacts which this ring satisfies.
3.These rings help in preventing substrate coupling.

Then block pins. how will u connect the large transistor terminals to devices outside the rings? we use the block pins.
 
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