Patent ID: 6779136
Filing Date: 2004-08-17
Classification: G11C

Abstract:
A method for testing a refresh device of an information memory having a multiplicity of cells, each cell having a minimum retention time and each cell storing information as a state of the respective cell, the refresh device refreshing the information before a guaranteed minimum retention time has elapsed, which comprises:providing a refresh selector for selecting a cell to be refreshed from a multiplicity of cells, the selector having a refresh address counter with a counting range of N counts; providing a sensor for sensing a state of each cell selected by the refresh selector; providing a restorer for setting each selected cell into a fresh state when in a refresh operating mode, the restorer refreshing a number N of cell groups of the memory each addressable by the refresh counter and representing the information derived from the sensed state, and having a test operating mode; verifying the respective states of each of the selected cells to produce a verified state for each cell; setting the fresh state for each selected cell to a predetermined state differing perceptively from a previously verified state with the restorer operating in the test operating mode before the guaranteed minimum retention time has elapsed; and checking if the states of the selected cells set in the test operating mode of the restorer correspond to the predetermined states; periodically emitting refresh clock pulses with a refresh clock for cyclically advancing the refresh address counter of the selector; and A) writing a known information item at the address of a chosen cell group within each of the N elements of the set which can be addressed by the refresh counter; B) applying a number X of refresh clock pulses with X=N while the restorer is being operated in the test operating mode before the guaranteed minimum retention time has elapsed; C) checking whether the states of the chosen cells set by the operation of the restorer correspond to the predetermined states after application of the X refresh clock pulses; applying a number Y of refresh clock pulses while the restorer is being operated in the refresh operating mode, where it is a number other than an integer multiple of N; and repeating the steps A) to C).