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Posted by Student (confused) on March 26, 2006, 5:30 pm
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I have a few conceptual questions. Tried posting in .basics newsgroup,
should have crossposted here, but too late now. When I get the answers,
I can just put them up here or there.
1. Does the top metal layer generally has lower resistance per unit
then all other layers? (I believe the answer is yes)
This question relates to self-heating:
2. In my course notes, there is a line saying "The top metal layer is
far away from substrate and is isolated by field oxide that is very low
thermal conductivity". The question is: Is that how we prevent self
heating or is that a bad thing that top metal layer is far away from...
3. Guard rings. When we use double guard ring, we need to connect one
guard ring to Vdd. It is obviously connected to different Vdd pad then
the
circuit. But these different Vdd pads can still be connected to the
same power supply?
4. Signal routing. This one has to do with the return currents.As you
know, the return currents are the highest in the nearest GND lines and
decrease with the increase in the distance from the signal line.The
question is: how come the current return in the closest signal line is
negligible?
Thanks for all the replies
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Posted by Nico Coesel on March 26, 2006, 5:43 pm
Please log in for more thread options
>I have a few conceptual questions. Tried posting in .basics newsgroup,
>should have crossposted here, but too late now. When I get the answers,
>I can just put them up here or there.
>
>1. Does the top metal layer generally has lower resistance per unit
>then all other layers? (I believe the answer is yes)
>
>This question relates to self-heating:
>2. In my course notes, there is a line saying "The top metal layer is
>far away from substrate and is isolated by field oxide that is very low
>
>thermal conductivity". The question is: Is that how we prevent self
>heating or is that a bad thing that top metal layer is far away from...
>
>
>3. Guard rings. When we use double guard ring, we need to connect one
>guard ring to Vdd. It is obviously connected to different Vdd pad then
>the
>circuit. But these different Vdd pads can still be connected to the
>same power supply?
>
>4. Signal routing. This one has to do with the return currents.As you
>know, the return currents are the highest in the nearest GND lines and
>decrease with the increase in the distance from the signal line.The
>question is: how come the current return in the closest signal line is
>negligible?
>
>Thanks for all the replies
The questions you ask have very little to do with VLSI design, but
more with basics like diodes and Ohm's law. Try to draw resistor/diode
equivalents.
--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
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>should have crossposted here, but too late now. When I get the answers,
>I can just put them up here or there.
>
>1. Does the top metal layer generally has lower resistance per unit
>then all other layers? (I believe the answer is yes)
>
>This question relates to self-heating:
>2. In my course notes, there is a line saying "The top metal layer is
>far away from substrate and is isolated by field oxide that is very low
>
>thermal conductivity". The question is: Is that how we prevent self
>heating or is that a bad thing that top metal layer is far away from...
>
>
>3. Guard rings. When we use double guard ring, we need to connect one
>guard ring to Vdd. It is obviously connected to different Vdd pad then
>the
>circuit. But these different Vdd pads can still be connected to the
>same power supply?
>
>4. Signal routing. This one has to do with the return currents.As you
>know, the return currents are the highest in the nearest GND lines and
>decrease with the increase in the distance from the signal line.The
>question is: how come the current return in the closest signal line is
>negligible?
>
>Thanks for all the replies