Altera ALTDLL Bedienungsanleitung PDF herunterladen (Seite 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

1 2 ... 48 49 50 51 52 53 54 55 56 57 58 ... 116 117

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Altera ALTDLL Bedienungsanleitung Seite 53