Read and Write VREF Calibration - 1.0 English

This section describes the V_REF calibration algorithm. The algorithm is the same for Read DQ V_REF and Write DQ V_REF calibration.

V_REF calibration starts at a default V_REF and the horizontal window at the default V_REF is recorded as Vref_max_h. Next, V_REF is incremented by a pre-defined step size. After each step size increments, the horizontal window size will be calculated and compared with the previous detected windows. If the current horizontal window is bigger than all the other windows, the current V_REF is recorded as Vref_max_h, and its horizontal window is recorded as W_max_r.

V_REF increments by step size continues until the horizontal window at a V_REF goes down to N × W_max_r; 0 < N < 1. The V_REF value where the horizontal window is less than N × W_max_r is recorded as Vref_min_h.

In some cases, two Vref_min_h points can be found before (Vref_lb) and after (Vref_ub) finding the Vref_max_h. The final V_REF point will be set to (Vref_ub – Vref_lb) / 2.

In other cases, Vref_lb cannot be detected while increasing the V_REF. In such cases, V_REF will be reverted back to the default value and decremented by the step size until it finds the Vref_lb point. While decrementing, there can be cases where the horizontal window starts increasing and a new Vref_max_h point can be found with a bigger horizontal window than W_max_r. In this case, the final V_REF is set to the center of the new Vref_min_h points.