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khorlipmin
Joined: 03 Jan 2005
Posts: 55
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 19 Aug 2006 11:37 Guard Ring |
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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
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jerryzhao
Joined: 08 Oct 2005
Posts: 156
Helped: 18
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| 19 Aug 2006 15:08 Guard Ring |
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| 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.
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safwatonline
Joined: 19 Nov 2005
Posts: 1352
Helped: 164
Location: EGYPT
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| 19 Aug 2006 15:13 Guard Ring |
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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
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khorlipmin
Joined: 03 Jan 2005
Posts: 55
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| 20 Aug 2006 12:47 Re: Guard Ring |
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So the guard ring is grounded? gnd! not Vdd! ?
Then should I be adding PPLUS at the diffusion contact area along the guard ring?
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safwatonline
Joined: 19 Nov 2005
Posts: 1352
Helped: 164
Location: EGYPT
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| 20 Aug 2006 12:59 Guard Ring |
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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"
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muiyuen
Joined: 25 Jan 2006
Posts: 44
Helped: 2
Location: Malaysia
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| 21 Aug 2006 3:31 Re: Guard Ring |
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Hi safwatonline, khorlipmin,
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| 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 |
This is from The Art of Analog Layout by Alan Hastings, they have one topic on guard rings.
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khorlipmin
Joined: 03 Jan 2005
Posts: 55
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| 21 Aug 2006 14:59 Re: Guard Ring |
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| 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?
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safwatonline
Joined: 19 Nov 2005
Posts: 1352
Helped: 164
Location: EGYPT
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| 21 Aug 2006 15:15 Guard Ring |
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| u can guard ring all blocks , i think it is up to u
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soorajsram
Joined: 06 Jan 2006
Posts: 39
Helped: 7
Location: Bangalore
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| 22 Aug 2006 8:07 Re: Guard Ring |
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Please go through the book The Art of Analog Layout, you get almost all your
doubts answered.
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khorlipmin
Joined: 03 Jan 2005
Posts: 55
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| 22 Aug 2006 10:59 Guard Ring |
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| yeah, i have ordered the book. on its way, cheers!
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safwatonline
Joined: 19 Nov 2005
Posts: 1352
Helped: 164
Location: EGYPT
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| 22 Aug 2006 11:02 Guard Ring |
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dont order it
it is available for free here
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khorlipmin
Joined: 03 Jan 2005
Posts: 55
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| 22 Aug 2006 12:03 Guard Ring |
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| thanks for the info, luckily i didnt pay for it, just ordered through the uni library
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leelamadhav
Joined: 19 Aug 2006
Posts: 22
Helped: 3
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| 23 Aug 2006 9:39 Re: Guard Ring |
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| 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
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drasta
Joined: 15 Sep 2004
Posts: 26
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| 23 Aug 2006 10:12 Re: Guard Ring |
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| 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.
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qutang
Joined: 25 Oct 2004
Posts: 315
Helped: 6
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| 24 Aug 2006 11:14 Guard Ring |
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| it can avoid latch-up ,i think
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