7.7.4.1 DQS[x] and DQ[x] Routing Specification
DQS[x] lines are point-to-point differential and DQ[x] lines are point-to-point single ended. Figure 7-27 and Figure 7-28 represent the supported topologies. Figure 7-29 and Figure 7-30 show the DQS[x] and DQ[x] routing. Figure 7-31 shows the DQLM for the LPDDR2 interface.
Trace routing specifications for the DQ[x] and the DQS[x] are specified in Table 7-20.
Table 7-20 DQS[x] and DQ[x] Routing Specification(1)(2)
NO. |
PARAMETER |
MIN |
TYP |
MAX |
UNIT |
1 |
DQ0 nominal length(3)(4)
|
|
|
DQLM0 |
mils |
2 |
DQ1 nominal length(3)(5)
|
|
|
DQLM1 |
mils |
3 |
DQ2 nominal length (3)(6)
|
|
|
DQLM2 |
mils |
4 |
DQ3 nominal length (3)(7)
|
|
|
DQLM3 |
mils |
5 |
DQ[x] skew(8)
|
|
|
10 |
ps |
6 |
DQS[x] skew |
|
|
5 |
ps |
7 |
Via count per each trace in DQ[x], DQS[x] |
|
|
2 |
|
8 |
Via count difference across a given DQ[x], DQS[x] |
|
|
0 |
|
9 |
DQS[x]-to-DQ[x] skew(8)(9)
|
|
|
10 |
ps |
10 |
Center-to-center DQ[x] to other LPDDR2 trace spacing(10)(11)
|
4 |
|
|
w |
11 |
Center-to-center DQ[x] to other DQ[x] trace spacing(10)(12)
|
3 |
|
|
w |
12 |
DQS[x] center-to-center spacing(13)
|
|
|
|
|
13 |
DQS[x] center-to-center spacing to other net(10)
|
4 |
|
|
w |
- DQS[x] represents the DQS0, DQS1, DQS2, DQS3 clock net classes, and DQ[x] represents the DQ0, DQ1, DQ2, DQ3 signal net classes.
- External termination disallowed. Data termination should use built-in ODT functionality.
- DQLMn is the longest Manhattan distance of a byte.
- DQLM0 is the longest Manhattan length for the DQ0 net class.
- DQLM1 is the longest Manhattan length for the DQ1 net class.
- DQLM2 is the longest Manhattan length for the DQ2 net class.
- DQLM3 is the longest Manhattan length for the DQ3 net class.
- Length matching is only done within a byte. Length matching across bytes is not required.
- Each DQS clock net class is length matched to its associated DQ signal net class.
- Center-to-center spacing is allowed to fall to minimum for up to 1000 mils of routed length.
- Other LPDDR2 trace spacing means signals that are not part of the same DQ[x] signal net class.
- This applies to spacing within same DQ[x] signal net class.
- DQS[x] pair spacing is set to ensure proper differential impedance. Differential impedance should be Zo x 2, where Zo is the single-ended impedance.