8片 DDR Layout Guidelines and Topology:

tzwhzf · 发表于 2009-8-1 13:54

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Layout Guidelines and Topology:
The following are the routing guidelines followed for DDR memory interface section:
1. Controlled impedance for single ended trace is Z0 = 60 ohm.
2. DQ, strobe, and clock signals are referenced to VSS.
3. Address, command, and control signals are referenced to VDD.
4. The length of address, command, and control signals are matched to clock with +/- 100 mil
tolerance.
5. DQ <0..7> & DM signals are length matched with respect to DQS with +/- 100 mil tolerance
(byte lane).
6. Each byte lanes are routed on same layer.
7. Byte lane to byte lane is matched to clock with +/- 500 mils.
8. CK & CK# are matched with +/- 30 mil and are routed as diff pair with 120 ohm differential
impedance.
9. Clock - pair to pair matching tolerance is +/- 30 mil.
10. Trace to trace spacing is 2X and signal group to group spacing is 3X.
11. DQS signals are routed in the middle of the byte lane (DQ<0..7>).
12. Clock trace split point to DRAM is less than 1 inch.
13. VTT and VREF islands are separated with the minimum spacing of 150mils.
14. VTT island width = 150 mil min.; 250 mil preferred.
15. VREF signal is routed with 20–25 mil minimum trace.
15. All signals are routed with minimum of 3X spacing between other signals
16. Layer biasing is followed for dual strip layers.
Figure 1 shows the data bus topology and figure 2 shows the address/control bus topology.