hello,

i've got a negative (ECL) and a positive (TTL) power plane 
on a board i'm doing.  right now i'm figuring on a matching
ground plane for each power supply, spaced close to the 
rail for switching capacitance.  here's the stack i'm 
thinking of:

critical traces
gnd
-5.2V
noncritical traces
noncritical traces
+5V
gnd
critical traces

does this seem reasonable?  i have some semblance of controlled
impedance with each trace layer referenced to a dc plane.
other stacks suggestions are welcomed.

but i need both the ground planes common to each other.  
can i EVEN have two planes called GND?  is having two ground
planes a bad idea?  if two ground planes is not a bad idea, 
then how do i tie them together?  NOTE:  if i tie them together
i would like to do it in a way that doesn't mess up my design
rules check.  i've noticed that additional vias and traces 
added to a pcb outside the schematic can make the design rules
check flag them.

i have another question.  this is iffy, but i'm a heathen
designer anyway.  this is just a proto board, and although i'd
like controlled impedance, i don't want to pay for it.  SO, 
what i am thinking is that if i get an 8-layer board at the
standard 62 mil thickness, that they are going to be just about
forced to give me between 6 to 8 mils between layers, without
me ever having to spec it.  does this sound right? 

thank you, miker

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