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Question of guard ring when layout

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usuikazkou

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Hi guys,
I am new to high speed design, recently I am trying to layout a 5Ghz circuit using tsmc180nm tech. When starting layout using rfmos of tsmc, all of the rfmos have guard ring added by default , I wonder if it necessary each of the rfnmos have guard ring?
or lets say we have a main circuit with 3 subcircuit, usually we will add guard ring to subcircuit(ex:each of subcircuit have 5~12 transistors) or we add guard ring to all transistor for high speed design?

thank you
 

usuikazkou said:
Hi guys,
I am new to high speed design, recently I am trying to layout a 5Ghz circuit using tsmc180nm tech. When starting layout using rfmos of tsmc, all of the rfmos have guard ring added by default , I wonder if it necessary each of the rfnmos have guard ring?
or lets say we have a main circuit with 3 subcircuit, usually we will add guard ring to subcircuit(ex:each of subcircuit have 5~12 transistors) or we add guard ring to all transistor for high speed design?

thank you
Click to expand...

In my opinion, it is safe to not add all guard ring in rfmos in the begining.

Let's consider about the priority of your layout requirement. If it put area higher than precise of guard ring protection, you can choose other normal mos without guard ring, layout them first by block or group, then surround this block with guard ring.
Because the difference is only guard ring so LVS check will pass without problem.
 
quyleanh said:
In my opinion, it is safe to not add all guard ring in rfmos in the begining.
.
Click to expand...

Thank you for your reply,
why it is safe when not add all guard ring in rfmos from the beginning?
 
Control of the body is important to things like FET fmax
(Cdb fights for gate authority, with Rgg if the body is let
to bounce), intermodulation / distortion. Loosening the
guardring spacing to the core channel will raise Rbb and
potentially put you outside modeled operation for the
RF FET (maybe more like what you see for "digital" ones
(or more like what you -don't- see...).
 
dick_freebird said:
Control of the body is important to things like FET fmax
(Cdb fights for gate authority, with Rgg if the body is let
to bounce), intermodulation / distortion. Loosening the
guardring spacing to the core channel will raise Rbb and
potentially put you outside modeled operation for the
RF FET (maybe more like what you see for "digital" ones
(or more like what you -don't- see...).
Click to expand...

Sir,
Can you explain more in detail?

dick_freebird said:
Loosening the
guardring spacing to the core channel will raise Rbb and
potentially put you outside modeled operation for the
RF FET (maybe more like what you see for "digital" ones
(or more like what you -don't- see...).
Click to expand...

Do you mean it will cause the simulation result inaccurate?

thank you
 

usuikazkou said:
Thank you for your reply,
why it is safe when not add all guard ring in rfmos from the beginning?
Click to expand...

Because the purpose of guard ring is separating all rfmos to other devices in circuit.
As long as you separate all rfmos (before or after), the protection purpose is satisfied.
 

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