the offset register 15 is decreased by 5 units per load command from the refresh counter 16 the enable signal 20 is still not generated so that the modifying y value yd is equal to the offset value ya during the succeeding degradation mode 52 with s 7 and f 2 the enable signal 19 is not generated to specify an incremental step of 7 units per 2 refresh clock cycles the offset value ya in the offset register 15 is increased by 7 units per load command from the refresh counter 16 however the enable signal 20 is generated so that the offset value ya is complemented to obtain the modifying y value yd during the following recovery mode 53 with s 3 and f 4 the enable signal 19 is generated to specify a decremental step of 3 units per 4 refresh clock cycles thus the offset value ya in the offset register 15 is decreased by 3 units per load command from the refresh counter 16 the enable signal 20 is also generated since the current operating mode is a recovery from degradation such that the offset value ya is complemented to obtain the modifying y value yd finally during the normal mode 54 the mode controller 11 activates the saturating circuit 14 to always clip.