Optimal data eye for improved Vref margin
An optimized method and apparatus for determining optimal DQS delay for DDR memory interfaces are disclosed. The method performs data eye training in a two dimensional space with time delay value as x-axis and reference voltage (Vref) as y-axis to determine a rectangular data eye within an overall data eye with Vref margin.
1. A method of performing data eye training using a data pattern in a two dimensional space of time versus voltage for aligning a data strobe of a memory device, comprising the steps:
validating the data pattern at a voltage reference (“Vref”) to determine a lower segment AB;
increasing the reference voltage by a margin voltage (“Vref+margin”);
validating the data pattern to determine an upper segment CD in the two dimensional space based on the increased Vref+margin;
validating the data pattern to determine a second lower segment AB′ in the two dimensional space;
validating the data pattern to determine a second upper segment CD in the two dimensional space; and
setting the data strobe to the middle of the second lower segment AB′ and the second upper segment C′D,
wherein the lower segment AB and the upper segment CD are within a data eye for the memory device, and
wherein the second upper segment AB′ and the second lower segment C′D form a largest rectangle within the lower segment AB and upper segment CD.
2. The method of claim 1 , wherein the step of validating the data pattern to determine a lower segment AB′ in the two dimensional space includes:
validating the data pattern to determine a lower left data start point A in the two dimensional space; and
validating the data pattern to determine a lower right data start point B′ in the two dimensional space.
3. The method of claim 1 , wherein the step of validating the data pattern to determine an upper lower segment C′D in the two dimensional space includes:
validating the data pattern to determine an upper left data start point C′ in the two dimensional space based on the increased Vref+margin; and
validating the data pattern to determine an upper right data start point D in the two dimensional space based on the increased Vref+margin.
4. The method of claim 1 , wherein the second lower segment AB′ defines a DQS timing margin within the rectangular data eye.
5. The method of claim 1 , wherein the second upper segment C′D defines a DQS timing margin within the rectangular data eye.
6. The method of claim 1 wherein the largest rectangle is compared with a previous largest rectangle, wherein if the largest rectangle is greater in area than the previous largest rectangle, then the largest rectangle is stored as the previous largest rectangle.
7. The method of claim 6 wherein the data strobe is set to the middle of the previous largest rectangle.
8. The method of claim 1 , in the validating the data pattern to determine the second upper segment step C′D, wherein if the increased Vref+margin is not equal to an ending reference voltage, then the increased Vref+margin is incremented by a reference voltage step size and wherein the method steps are repeated starting at the validating the data pattern to determine the upper segment CD using the incremented Vref+margin.
9. The method of claim 1 wherein the lower segment for the voltage reference Vref meets a minimum eye width within a data eye for the memory device.
10. The method of claim 1 , in the validating the data pattern to determine the upper segment CD step, wherein if the upper segment CD does not meet a minimum eye width within a data eye for the memory device, then recurse back to and start at the increasing the reference voltage step.