Questions on "PC2-5300" DDR2 Schematic designs.
Abhi P Choksi , 06-01-2020, 07:39 AM
Hi all,
I am design PC2-5300 DDR2 design just for practicing of DDR routing and Design.I have taken reference of PC2-5300 design files available on JEDEC site.
I have several questions on schematic design for which i want explanation from this Forum.
(1)Why Clock is terminated in 200 ohms instead of 100 ohms?
(2)Why there is no common mode termination used for clocks?
(3)What is purpose of small capacitor(eg. C5) in parallel with Clock termination?
(4)What is purpose of Series termination resistors like 22R even we have support of ODT?. Also i can not understand why 22R is there on DIMM because it must be near to sources.
I am design PC2-5300 DDR2 design just for practicing of DDR routing and Design.I have taken reference of PC2-5300 design files available on JEDEC site.
I have several questions on schematic design for which i want explanation from this Forum.
(1)Why Clock is terminated in 200 ohms instead of 100 ohms?
(2)Why there is no common mode termination used for clocks?
(3)What is purpose of small capacitor(eg. C5) in parallel with Clock termination?
(4)What is purpose of Series termination resistors like 22R even we have support of ODT?. Also i can not understand why 22R is there on DIMM because it must be near to sources.
robertferanec , 06-06-2020, 02:23 AM
I will not really give you answers what you are looking for 
1) it looks to me there are actually 3x 200OHMs in parallel (66OHMs in total)
2) 3) 4) I would expect, these may be results of simulations to improve the signal quality.
PS: I was also thinking about the series resistors ... and only what come up to my mind was maybe to help with influence of connector(?). But that is only guessing, it may be something completely different. Also, the resistors will be close to the outputs when reading from the memory.
1) it looks to me there are actually 3x 200OHMs in parallel (66OHMs in total)
2) 3) 4) I would expect, these may be results of simulations to improve the signal quality.
PS: I was also thinking about the series resistors ... and only what come up to my mind was maybe to help with influence of connector(?). But that is only guessing, it may be something completely different. Also, the resistors will be close to the outputs when reading from the memory.
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