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Design >> Mixed-Signal Design >> Confused about the Role of N+ and P+ Guard Ring
https://designers-guide.org/forum/YaBB.pl?num=1340714203

Message started by waosai on Jun 26^th, 2012, 5:36am

Title: Confused about the Role of N+ and P+ Guard Ring
Post by waosai on Jun 26^th, 2012, 5:36am

Hi everyone, I have a question concerning the role of the guard ring.

(1)Someone told me that N+ on NW connected to VDD blocks electron and P+ on psub connected to GND absorbs electron. But someone else also told me that the former absorbs electron and the latter absorbs hole. So which one on earth is correct: absorb or block?

(2)Is there any sequence for double GRs? ie. external ring for N+ on NW and internal ring for P+ on psub, or vice versus. If yes, which one is correct or better?

(3) Is such sequence the same for the aggressor block and viticm block?

(4)Can we use N+ on psub connected to VDD and P+ on NW connected to GND as GR

Thanks a lot !

Title: Re: Confused about the Role of N+ and P+ Guard Ring
Post by BackerShu on Jul 24^th, 2012, 3:41pm

As I remember, most of these things are covered in Alan Hastings book: The Art of Analog Layout.

Title: Re: Confused about the Role of N+ and P+ Guard Ring
Post by Lynn Lou on Aug 18^th, 2012, 7:10pm

Hi, your question about N/p-doping, N+/P+ -doping is actually a matter of process. Please keep in mind, the GR effect are based on the diode effect of a PN junction. And the heavy doping (N+/P+) is generally for improving the conductivity to the doped well. Both of P+ on psub and N+ on NW let go the current, but the question is : what contribute to it, Elec or Hole? The answer is P doping creates Holes while N doping Elecs. A Hole is actually a created unit, and it means there is no Elec at where a Hole stands. Now I believe you get your answers.

About Q.4, I think you can not directly place an N+ on psub or P+ on NW in standard process. As mention above, heavy doping is just for improving conductivity, and NW and PW are used as GRs.