Altera ALTDLL - Manual (Page 53)

4–17 Chapter 4: Functional Description
Delay Chains
ALTDLL and ALTDQ_DQS Megafunctions User Guide © February 2012 Altera Corporation
The SSN is induced when adjacent pins in a DQ bus that toggle at the same time
(especially at a high frequency) induces noise that affects signal integrity. To ensure
that the adjacent pins in a DQ bus are not toggled at the same time, deskew delay
chains are used to provide small amounts of delay. Refer to
Figure 4–9 .
You can access these delay chains in the ALTDQ_DQS megafunction for the DQ Input
Path (D1) and DQ Output Path (D5 and D6). These 50 ps step delay chains provide
small amounts of delay.
1 You must create a custom calibration circuit to control these delay chains to reduce
SSN.
Figure 4–9. Reduce SSN Using Deskew Delay Chains
700 ps
5 ns
5 ns