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    briefly explain about Guard rings in CMOS

    What is a guard ring in CMOS. What is its function?

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    Re: briefly explain about Guard rings in CMOS

    cmos combination combine NMOS and PMOS structure . In some cases the N and P structure use in each process can create a parasitic path between the supply and the ground. By using a guard ring the designer can reduce these parasitics effects(NPN-PNP parasitic transistors created ).

    - - - Updated - - -

    The parasitic effect in this case is called : latchup


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    Re: briefly explain about Guard rings in CMOS

    and more, the latch up is basically a SCR circuit. If it turns on, it runs fastly to an increasing current due to positive feedback casuing malfunctioning or even destruction


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    •   Alt5th June 2012, 13:08

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    Re: briefly explain about Guard rings in CMOS

    There are two uses for guard rings. One is to make the
    lowest practical Rb on the parasitic transistor structure.
    Some foundries only require that you respect a minimum
    "distance to tap" but a guardring can improve this worst
    case extrinsic base resistance by a couple of decades.
    In flows where the looser construction style is allowed
    in the core you may still see guardrings called out in the
    I/O or ESD device rules.

    The other use is to backstop any field or well surface
    inversion, which may occur in lighter doped or lousier-
    field-oxide processes, or in the presence of ionizing
    radiation.



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    Re: briefly explain about Guard rings in CMOS

    avoid latch—up.



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    Re: briefly explain about Guard rings in CMOS

    Guard ring is added across a sensitive analog circuit to isolate it from any substrate noise from digital or some high frequency switching circuit..


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    •   Alt17th June 2012, 16:01

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    Re: briefly explain about Guard rings in CMOS

    please everyone explain in detail , why Guard ring can suppress latch-up phenomenon ?



    •   Alt18th June 2012, 10:21

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    Re: briefly explain about Guard rings in CMOS

    Guard ring is added across a sensitive analog circuit to isolate it from any substrate noise from digital or some high frequency switching circuit..As you might know, an unintentionally created latch can be triggered (turned-on) by a noise spike from digital circuit. Once the latch is turned on, it can destroy the chip by sucking large amount of current.



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    Re: briefly explain about Guard rings in CMOS

    Guard rings are mainly used to avoid Latchup .in CMOS technolog.Latchup occurs due o the parsitic PNPN structure which is formed when both PMOS and NMOS kept at proximity



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    Re: briefly explain about Guard rings in CMOS

    I know that Guard ring is used to prevent the latch-up problem. But how? I have never seen a guard ring. Where do you actually place it?

    Thanks a lot
    Mind is like a room. You have to keep only useful things in that room.



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    Re: briefly explain about Guard rings in CMOS

    Guard Ring is in my opinion is just P-tap or N-tap connected to VSS or VDD.



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    Re: briefly explain about Guard rings in CMOS

    Quote Originally Posted by VLSI_Learner View Post
    Guard Ring is in my opinion is just P-tap or N-tap connected to VSS or VDD.
    Your opinion neglects geometry and completeness.



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    Re: briefly explain about Guard rings in CMOS

    Means? Can you please explain?



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    Re: briefly explain about Guard rings in CMOS

    "Taps" are single contacts. To suppress leakage completely
    you need a fence, not one fencepost. Similarly for extracting
    substrate currents, you need to kill the entire parasitic "base"
    wherever it may lie. A point contact would have to be lucky
    or smart. A guard ring is complete and doesn't need to know
    anything about its context.



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    Re: briefly explain about Guard rings in CMOS

    Hi everyone,
    Can somebody tell me what is a double guard ring, and what is its advantage over single guard ring??



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