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11/19/08 15:20
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 		 #160133 - I also recommend a 4-layer Board
Responding to: ???'s previous message
I too would recommend a 4-layer board. I would one further and do the following...

- Carve out an analogue ground island portion and connect back to digital GND at or near the processor.

- Match the analogue ground island with an mating analogue power island.

- Make sure no traces cross over the plane splits between the digital continent and the analogue island area. Have any necessary signals cross in/out at the place where the island connects to the mainland and isolate with ferrite beads or multilayer type inductors.

I totally agree with ERIK regarding achievable resolution with MCU on chip A/D converters. Using the above type recommendations I have had good luck using the 10-bit coverters in AVR and COLDFIRE parts without going to sleep during conversions. Using the 12-bit converters in SiLabs type parts I realized somewhere maybe 10 - 11 bits at best. In all cases rolling average sampling filters were used.

Michael Karas


List of 33 messages in thread
TopicAuthorDate
PCB routing question            01/01/70 00:00      
   once conneced inside ...            01/01/70 00:00      
   Maybe these links can help...            01/01/70 00:00      
      Is this ok            01/01/70 00:00      
         This is no PIC forum!            01/01/70 00:00      
            Not so            01/01/70 00:00      
               being in chat and the question having merit ...            01/01/70 00:00      
                  So you give me benefit of doubt :-)            01/01/70 00:00      
                     if two things are both beneficial ...            01/01/70 00:00      
                     I also recommend a 4-layer Board            01/01/70 00:00      
                        10-bit            01/01/70 00:00      
                           The rolling filters...            01/01/70 00:00      
                              changed            01/01/70 00:00      
                                 Wrong!            01/01/70 00:00      
                                    Consider this alternate            01/01/70 00:00      
                                       Exactly, that's what I meant!            01/01/70 00:00      
                                          Microchip people seems careless            01/01/70 00:00      
                                             Yes            01/01/70 00:00      
                                                To be on the safe side..            01/01/70 00:00      
                                                   Please compare and see...            01/01/70 00:00      
                                             Argh...not another chip here...            01/01/70 00:00      
                                                Oscillator pins as noise source            01/01/70 00:00      
                                                   Yes, the promises sound good...            01/01/70 00:00      
                                                      Differential mode advice            01/01/70 00:00      
                                                         I cannot see a differential mode            01/01/70 00:00      
                                                            Jpg format            01/01/70 00:00      
                                                               jpeg not so good for computer-generated images            01/01/70 00:00      
                                                            One point missed            01/01/70 00:00      
                                                               The SMPS should be enough of a reason            01/01/70 00:00      
                                    Great!            01/01/70 00:00      
                                       you have already lost the battle ...            01/01/70 00:00      
                                          Containing the damage            01/01/70 00:00      
                                             "hope springs eternal" ...            01/01/70 00:00      

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