Patent ID: 7239553

Claim:
A storage device having a reference cell to be referred to when determining the data state of a memory cell, the storage device comprising: a first reference unit for defining a lower limit state for the reference cell; a second reference unit for defining an upper limit state for the reference cell; a comparator for comparing a reference data state of the reference cell to the lower limit state and the upper limit state and determine whether the reference data state of the reference cell is below the lower limit state, above the upper limit state, or between the lower limit state and the upper limit state; and a control unit coupled to the comparator for adjusting the reference data state in response to comparison of the reference data state to the lower limit state and the upper limit state, wherein the control unit initializes the reference cell when the comparator determines that the reference data state is below the lower limit state or above the upper limit state and thereafter relaxes an adjustment bias voltage applied to the reference cell and adjusts the reference data state.