7.3.4. Phase Offset Control
Each DLL has two phase-offset modules and can provide two separate DQS delay settings with independent offsets, one for the top and bottom I/O bank and one for the left and right I/O bank, so you can fine-tune the DQS phase-shift settings between two different sides of the device. Even though you have independent phase offset control, the frequency of the interface using the same DLL must be the same. Use the phase offset control module for making small shifts to the input signal and use the DQS phase-shift circuitry for larger signal shifts. For example, if the DLL only offers a multiple of a 45° phase shift, but your interface must have a 97.5° phase shift on the DQS signal, you can use two delay chains in the DQS logic blocks to give you a 90° phase shift and use the phase offset control feature to implement the extra 7.5° phase shift.
You can use either a static phase offset or a dynamic phase offset to implement the additional phase shift. The available additional phase shift is implemented in 2’s complement in Binary-code between settings –128 to +127. An additional bit indicates whether the setting has a positive or negative value. The settings are linear, each phase offset setting adds a specified delay amount. The DQS phase shift is the sum of the DLL delay settings and the user-selected phase offset settings whose top setting is 128, so the actual physical offset setting range is 128 subtracted by the DQS delay settings from the DLL.
When using this feature, you must monitor the DQS delay settings to know how many offsets you can add and subtract in the system. The DQS delay settings output by the DLL are also Gray coded.
For example, if the DLL determines that DQS delay settings of 28 is required to achieve a 30° phase shift, you can subtract up to 28 phase offset settings and you can add up to 99 phase offset settings to achieve the optimal delay that you require.
For more information about the value for each step and the specified delay amounts for the phase offset setting, refer to the Stratix® V.
When using static phase offset, you can specify the phase offset amount in the UniPHY IP core as a positive number for addition or a negative number for subtraction. You can also have a dynamic phase offset that is always added to, subtracted from, or both added to and subtracted from the DLL phase shift. When you add or subtract, you can dynamically input the phase offset amount into the offset[6..0] port. When you want to both add and subtract dynamically, you control the addnsub signal in addition to the offset[6..0] signals. The phase offset is not PVT-compensated.