----- Original Message -----
From: "Abd ul-Rahman Lomax" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Tuesday, June 26, 2001 1:55 PM
Subject: Re: [PEDA] Ground Planes Connection
|
| To connect at DC or low frequencies while isolating RF, an inductor would
| be used.
|
It's under these circumstances where I've sucessfully used printed inductors.
_____________
Brian Guralnick
----- Original Message -----
From: "Abd ul-Rahman Lomax" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Tuesday, June 26, 2001 1:55 PM
Subject: Re: [PEDA] Ground Planes Connection
| At 02:56 PM 6/26/01 +0200, Jerome DUMAS wrote:
|
| The advice to read the Signal Integrity list is good.
|
| >The pcb I'm currently designing features 3 differents ground planes
| >(digital, analog audio, and radio-frequency FM).
| >I've separated each plane by about 2mm gaps, my question is how to connect
| >the 3 ground planes, and where ?
|
| The answers to this question depend so much on circuit functions that it is
| difficult to give a single answer.
|
| Star connections radiating from an area containing the main bulk bypass
| capacitor ground pin are common.
|
| >For now, analog and digital planes are connected by a 2mm pcb wire directly
| >under the codec (pcm3002), and the RF ground plane is connected to the
| >analog ground plane through a 1nF ceramic cap (in order to avoid RF & audio
| >coupling).
|
| That 2mm PCB wire will cause DRC problems unless the schematic has only a
| single ground net for both the analog and digital planes. We've recommended
| the use of a virtual short for this purpose. On the schematic, it appears
| as a two-pin jumper; on the PCB, it is a footprint containing two pads (or
| pad/fill combinations, which can be a little easier to work with in this
| case) which have a gap of a few microinches. A design rule allows this
| particular part to have such a small clearance between pads. Such a gap
| cannot be fabricated, with many layers of impossibility. So DRC thinks that
| there are two nets while the physical PCB ends up with one continuous wire.
| Another advantage is that the process is schematic-controlled, and you
| cannot accidentally short together analog and digital grounds in any
| additional locations; DRC would detect this.
|
| As to the cap, it will efficiently couple RF into the analog ground plane,
| the opposite of what was stated. Such a cap would be used to couple RF
| and/or analog signals while maintaining DC isolation.
|
| To connect at DC or low frequencies while isolating RF, an inductor would
| be used.
|
| [EMAIL PROTECTED]
| Abdulrahman Lomax
| P.O. Box 690
| El Verano, CA 95433
|
|
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