Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

guard ring connections N+ and P+

Status
Not open for further replies.

nschutten

Member level 3
Joined
Jan 18, 2009
Messages
67
Helped
7
Reputation
14
Reaction score
2
Trophy points
1,288
Activity points
1,852
n+ ring

I have been looking into how to best guard rings and this is what I think up to now:
- in principle it is best to connect the P+ and N+ rings to their independent package pins
- however, when the maximum pin count is limited and/or when the amount of analog blocks is large, compromises have to be made
- the 'victim' block is isolated by P+ and N+ rings and these rings are connected to the analog blocks respective GND and VDD connections

Here are my questions:
- for the noise source block, a P+ ring is easily implemented (e.g. just down bond the guard ring connection); assuming that no dedicated pins are available any more for N+ ring connection, what should this be connected to? Or would it be best to leave out the N+ ring at the noise source all-together?
- to save pins, has anyone ever considered RC filtering the VDD line from another block to the N+ ring, so that no additional package pins are required, but that the N+ supply is still clean (cleaned up by the RC filtering)? This seems feasible, since the rings don't really carry current, so the RC time constant can be made sufficiently low without occupying much die area

Looking forward to anyone's thoughts and/or experience in this!
 

n+ guard ring

nschutten said:
... assuming that no dedicated pins are available any more for N+ ring connection, what should this be connected to? Or would it be best to leave out the N+ ring at the noise source all-together?
No. Just connect it to VDD .

nschutten said:
- to save pins, has anyone ever considered RC filtering the VDD line from another block to the N+ ring, so that no additional package pins are required, but that the N+ supply is still clean (cleaned up by the RC filtering)? This seems feasible, since the rings don't really carry current, so the RC time constant can be made sufficiently low without occupying much die area

Looking forward to anyone's thoughts and/or experience in this!
IMHO filtering the supply voltage of guardRings doesn't make sense. Their purpose is to
- catch straying electrons (N+ guardRings) or holes (P+ guardRings) to prevent them from triggering parasitic action (BJT or thyristor action)
- shield from noise
For both intended purposes, they should be connected directly to their appropriate voltage levels.
 
  • Like
Reactions: Imello

    nschutten

    Points: 2
    Helpful Answer Positive Rating

    Imello

    Points: 2
    Helpful Answer Positive Rating
guard ring connection

Thanks for sharing your thoughts on this.
When connecting an N+ ring at the noise source to VDD, would this then just be the VDD of this particular noise source or something else?
 

nschutten said:
Thanks for sharing your thoughts on this.
Thanks for your Thanks message!

nschutten said:
When connecting an N+ ring at the noise source to VDD, would this then just be the VDD of this particular noise source or something else?
I'd suggest the VDD connection with the least noise level, the "purest" VDD available. No further filtering. IMHO, an additional filter resistor just would attenuate the shielding function.
 

I have found that the guard ring connections need to be low impedance, in which case RC filtering is out of the question (this only increases the impedance).

Also, I have seen an UMC appnote where P+ N+ guard rings are used, but both are connected to GND.

Anyone has any experience with this?
 

nschutten said:
... Also, I have seen an UMC appnote where P+ N+ guard rings are used, but both are connected to GND.
Connecting N+ guard rings to GND wouldn't help much for their main designation: to suppress parasitic action possibly leading to latch-up. It would, however, still help to screen against noise.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top