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What's the purpose and application of a guard ring

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khorlipmin

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Can anyone explain the purpose of guard ring and what do I do with it? say if I have a gnd! guard ring, do I connect all the gnd to it? do I need another Vdd ring?
How do I connect to the IO pad then? still with the guard ring on?
Any link or decumentation would be helpful. thanks
 

latch-up well junction guard ring

one reason we add guard aroud analog circuit in order to shied the noise from digital substrate. At that time the guard can,t connect the digital power.
 

Guard Ring

high isnt the guard ring a reverse bias junction i.e. if the Substrate is P then the Guard ring is actually an N doping to make a BJT in OFF i.e. two back to back junction both in reverse

plz correct me if i am wrong
 

Re: Guard Ring

So the guard ring is grounded? gnd! not Vdd! ?
Then should I be adding PPLUS at the diffusion contact area along the guard ring?
 

Guard Ring

hI,
if what i said is correct, then to make a reverse bias the P should be connected to GND "which is a bulk tie" and the N should be connected to VDD "through some NPLUS"
 

Re: Guard Ring

Hi safwatonline, khorlipmin,

Guard rings prevent minority carriers injected by one device from interfering with the operation of another device. Not only do guard rings prevent latchup, but they also block noise coupling that might otherwise interfere with the operation of low-power circuitry
Click to expand...

This is from The Art of Analog Layout by Alan Hastings, they have one topic on guard rings.
 

Re: Guard Ring

so since I have a bias replica circuit, a VCO core and a output buffer, which one of the should the guard ring applied to? issit the whole chip or just the VCO core?
 

Guard Ring

u can guard ring all blocks , i think it is up to u
 

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    khorlipmin

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Re: Guard Ring

Please go through the book The Art of Analog Layout, you get almost all your
doubts answered.
 

Guard Ring

yeah, i have ordered the book. on its way, cheers!
 

Guard Ring

dont order it
it is available for free **broken link removed**
 
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Guard Ring

thanks for the info, luckily i didnt pay for it, just ordered through the uni library
 

Re: Guard Ring

The gaurd ring around PMOS which is in an n well is n+ gaurd ring which needs to be connected to VDD not p+... correct me if i am wrong
 

Re: Guard Ring

leelamadhav is right for NWELL you use nmoat guard ring connected to the VDD and for PWELL you use pmoat connected to the GND. It is usually to lower noise on board ant isolate the device usually analog.
 

Guard Ring

it can avoid latch-up ,i think
 

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