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Joseph Hebert
01/17/06 10:01
Read: 1120 times
Okemah, Ok
United States


 
#107612 - Separate signal traces.
Responding to: Suresh R's previous message
Hi Suresh,

First of all, what is the common salutation in Hindi? Just curious.

Second, The first thing you should do is simply segregate the signal traces into separate regions of the board. The return current from any one trace will try to follow that same trace, will try to stay directly under it, in the ground plane. This is because that is where the impedence between the trace and ground plane is lowest.

So if the traces are segregated, so will be the currents. It is extremely rare that anyone actually needs to physically split a ground plane into digital and analog parts. I know that every DAC manufacturer says that you should. Not to put too fine a point on the matter, but they're lying.

But if you really are that unlucky soul who has so offended God that He has punished you and you really do need to split your ground plane, then there is one peril that you must either understand or rely on dumb luck to avoid. Never, make that NEVER, let a trace cross the split. Has anyone here ever worked with microwave transmitters? Can you say "slot antenna?"

As I mentioned earlier, the impedence of the trace depends on the distance between it and the ground plane. When a trace crosses a split in the plane, it experiences an impulsive increase in impedance. This causes an abrupt change in velocity (an acceleration) of the electrons, and as everyone knows when you accelerate an electron you cause it to emit electromagnetic radiation.

These impedance impulses will cause your circuit board to spew EMI. They will also cause reflections and interferences, for both digital and analog signals.

The bottom line is that if you do split your ground plane, you absolutely better keep the traces segregated. And if you can do that sufficiently, then you probably didn't need to split the plane in the first place.

List of 56 messages in thread
TopicAuthorDate
Circuit Analysis      Suresh R      12/27/05 00:40      
   Analysis      Farshid Jafari Harandi      12/27/05 04:15      
   Dangerous!      Kai Klaas      12/27/05 07:09      
      bungling amateurs "bragging" on the web      Erik Malund      12/27/05 08:55      
         Not electronic, but an amusing example      Joseph Hebert      12/27/05 09:58      
            OLD idea ?      Steve M. Taylor      12/27/05 12:09      
               New and improved      Joseph Hebert      12/27/05 17:11      
                  Safety first      Steve M. Taylor      12/28/05 06:43      
         I think you meant...      Kalpak Dabir      12/27/05 10:01      
         deja vu all over again!      Andy Neil      12/27/05 18:23      
      resistor replaced by capacitor      Suresh R      12/28/05 01:11      
         Phase shift      Kai Klaas      12/28/05 06:30      
         dissapation      Terry Lingle      12/28/05 06:38      
            Dissipation      Steve M. Taylor      12/28/05 06:48      
               It's a real world after all      Terry Lingle      12/28/05 07:11      
                  What ? Make mistakes ?      Steve M. Taylor      12/28/05 07:33      
                     are you sure      Erik Malund      12/28/05 09:05      
                     or ..      Andy Curda      12/29/05 13:21      
            Non ideal cap performance      Kai Klaas      12/28/05 06:58      
   Diodes!      Andy Neil      12/27/05 07:14      
   Current Limiting Capacitor      Joseph Hebert      12/27/05 09:47      
      Capacitor Filters      Suresh R      01/12/06 01:15      
         Some basic theory needed      Kalpak Dabir      01/12/06 01:25      
         12 */~2 ~ 17 so I doubt you see 19V      Erik Malund      01/12/06 06:31      
         Output voltage      Kai Klaas      01/12/06 07:54      
            Regulation      Steve M. Taylor      01/12/06 11:20      
            current flow      Suresh R      01/13/06 00:43      
               What current?      Kai Klaas      01/13/06 06:10      
                  What iam trying to know is      Suresh R      01/15/06 21:29      
                     inrush current      Terry Lingle      01/15/06 23:20      
                     Naiive analysis      Steve M. Taylor      01/16/06 06:33      
                        Laplace Transformation      Kai Klaas      01/16/06 07:19      
                           Could be worse....      Steve M. Taylor      01/16/06 11:39      
                              Me too!      Kai Klaas      01/16/06 11:58      
                                 Minds are failing      Steve M. Taylor      01/16/06 12:28      
                     DC component      Kai Klaas      01/16/06 12:03      
                        Suresh, have as look      Erik Malund      01/16/06 12:18      
                           analog and digital ground      Suresh R      01/17/06 00:24      
                              discussed ad nauseam do a search      Erik Malund      01/17/06 06:56      
                              Use a splitted ground plane      Kai Klaas      01/17/06 07:32      
                                 did i got it right      Suresh R      01/18/06 00:49      
                                    Also datasheet of ADUC can help you      Kai Klaas      01/18/06 06:44      
                                       Placing Vias      Suresh R      01/24/06 00:18      
                                          Maybe..      Kai Klaas      01/24/06 06:08      
                                             Copper fills      Terry Lingle      01/24/06 08:25      
                                          I do not know about 2 layers      Erik Malund      01/24/06 09:09      
                                        Auto route      Suresh R      01/25/06 00:00      
                                          Solid ground plane has to be solid!      Kai Klaas      01/25/06 08:37      
                                             Thank you Kai      Suresh R      01/26/06 21:12      
                                                circuit for a despensing unit      Suresh R      01/28/06 02:58      
                                                   ICM7555 + 2M2 + 68      Kai Klaas      01/28/06 10:14      
                                                      why a totally unrelated post in the midd      Erik Malund      01/30/06 08:07      
                              Separate signal traces.      Joseph Hebert      01/17/06 10:01      
                                 What has God to do with this??      Kai Klaas      01/17/06 19:20      
               DC DC      Steve M. Taylor      01/13/06 06:19      
               DC DC      Steve M. Taylor      01/13/06 06:19      

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