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  1. #1
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    Question of guard ring when layout

    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

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  2. #2
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    Re: Question of guard ring when layout

    Quote Originally Posted by usuikazkou View Post
    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
    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.



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  3. #3
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    Re: Question of guard ring when layout

    Quote Originally Posted by quyleanh View Post
    In my opinion, it is safe to not add all guard ring in rfmos in the begining.
    .
    Thank you for your reply,
    why it is safe when not add all guard ring in rfmos from the beginning?



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  4. #4
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    Re: Question of guard ring when layout

    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...).



  5. #5
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    Re: Question of guard ring when layout

    Quote Originally Posted by dick_freebird View Post
    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...).
    Sir,
    Can you explain more in detail?

    Quote Originally Posted by dick_freebird View Post
    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...).
    Do you mean it will cause the simulation result inaccurate?

    thank you



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  6. #6
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    Re: Question of guard ring when layout

    Quote Originally Posted by usuikazkou View Post
    Thank you for your reply,
    why it is safe when not add all guard ring in rfmos from the beginning?
    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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