184.108.40.206. DQS Phase-Shift
The DLL can shift the incoming DQS signals by 0°, 45°, 90°, or 135°. The shifted DQS signal is then used as the clock for the DQ IOE input registers.
All DQS/CQ/CQn pins referenced to the same DLL, can have their input signal phase shifted by a different degree amount but all must be referenced at one particular frequency. For example, you can have a 90° phase shift on DQS1T and a 45° phase shift on DQS2T, referenced from a 300-MHz clock. However, not all phase-shift combinations are supported. The phase shifts on the DQS pins referenced by the same DLL must all be a multiple of 45° (up to 135°).
The 7-bit DQS delay settings from the DLL vary with PVT to implement the phase-shift delay. For example, with a 0° shift, the DQS/CQ signal bypasses both the DLL and DQS logic blocks. The Intel® Quartus® Prime software automatically sets the DQ input delay chains, so that the skew between the DQ and DQS/CQ pins at the DQ IOE registers is negligible if a 0° shift is implemented. You can feed the DQS delay settings to the DQS logic block and logic array.
The shifted DQS/CQ signal goes to the DQS bus to clock the IOE input registers of the DQ pins. The signal can also go into the logic array for resynchronization if you are not using IOE resynchronization registers.
The input reference clock goes into the DLL to a chain of up to eight delay elements. The phase comparator compares the signal coming out of the end of the delay chain block to the input reference clock. The phase comparator then issues the upndn signal to the Gray-code counter. This signal increments or decrements a 7-bit delay setting (DQS delay settings) that increases or decreases the delay through the delay element chain to bring the input reference clock and the signals coming out of the delay element chain in phase.
The DLL can be reset from either the logic array or a user I/O pin (if 2,560 or 512 clock cycles applies). Each time the DLL is reset, you must wait for 2,560 (low-jitter mode) or 512 clock cycles for the DLL to lock before you can capture the data properly.
You can still use DQS phase-shift circuitry for memory interfaces running on frequencies below the minimum DLL input frequency, which is 300 MHz. The frequency of the clock feeding the DLL should be doubled when the interface frequency is between 150 MHz and 299 MHz or multiplied by four when the interface frequency is between 75 MHz and 149 MHz. Because of the changes on the DLL input clock frequency, the DQS delay chain can only shift up to 67.5° for the interface frequency between 150 MHz and 299 MHz and 33.75° for the interface frequency between 75 MHz and 149 MHz. Depending on your design, while the DQS signal might not shift exactly to the middle of the DQ valid window, the IOE is still able to capture the data accurately in low-frequency applications, where a large amount of timing margin is available.
For the frequency range of each DLL frequency mode, refer to the device datasheet.
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