Apparatus and method for performing target refresh operation

A semiconductor memory device, comprising:

• a reference signal generator configured to generate a reference signal having enable periods, wherein a number of the enable periods and length of each enable period are randomly determined based on operation time;
• first storage logic configured to store, as first addresses, maximum ‘K’ addresses having different values among input addresses applied during the enable period of the reference signal;
• second storage logic configured to store, as second addresses, ‘L’ addresses corresponding to a time point at which the enable period of the reference signal is ended, among the input addresses applied during the enable period of the reference signal;
• an order controller configured to determine output or non-output and a first output order of each of the first addresses based on a number of times each of the first addresses is repeatedly input, and to determine a second output order for outputting mixed addresses obtained by mixing the first addresses based on the first output order and the second addresses together;
• and
• refresh operation logic configured to apply the mixed addresses, which are output by the order controller according to the second output order, to a target refresh operation,
• wherein ‘K’ is a natural number equal to or greater than 2, and ‘L’ is a natural number equal to or greater than 1.