Patent Publication Number: US-2021166752-A1

Title: Apparatuses and methods for distributed targeted refresh operations

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 16/232,837, filed Dec. 26, 2018. This application is incorporated by reference herein in its entirety and for all purposes. 
    
    
     BACKGROUND 
     Information may be stored on individual memory cells of the memory as a physical signal (e.g., a charge on a capacitive element). The memory may be a volatile memory, and the physical signal may decay over time (which may degrade or destroy the information stored in the memory cells). It may be necessary to periodically refresh the information in the memory cells by, for example, rewriting the information to restore the physical signal to an initial value. 
     As memory components have decreased in size, the density of memory cells has greatly increased. An auto-refresh operation may be carried out where a sequence of memory cells are periodically refreshed. Repeated access to a particular memory cell or group of memory cells (often referred to as a ‘row hammer’) may cause an increased rate of data degradation in nearby memory cells. It may be desirable to identify and refresh memory cells affected by the row hammer in a targeted refresh operation in addition to the auto-refresh operation. The targeted refresh operations may occur with timing interspersed between the auto-refresh operations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a semiconductor device according to an embodiment of the present disclosure. 
         FIG. 2  is a block diagram of a refresh control circuit according to an embodiment of the present disclosure. 
         FIG. 3  is a block diagram of an address sampler according to an embodiment of the present disclosure. 
         FIG. 4  shows a timing diagram of a refresh operations according to an embodiment of the present disclosure. 
         FIG. 5  shows a timing diagram of refresh operations according to an embodiment of the present disclosure. 
         FIG. 6  shows a timing diagram of refresh operations according to an embodiment of the present disclosure. 
         FIG. 7  shows a timing diagram of internal signals of a refresh control circuit according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of certain embodiments is merely exemplary in nature and is in no way intended to limit the scope of the disclosure or its applications or uses. In the following detailed description of embodiments of the present systems and methods, reference is made to the accompanying drawings which form a part hereof, and which are shown by way of illustration specific embodiments in which the described systems and methods may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice presently disclosed systems and methods, and it is to be understood that other embodiments may be utilized and that structural and logical changes may be made without departing from the spirit and scope of the disclosure. Moreover, for the purpose of clarity, detailed descriptions of certain features will not be discussed when they would be apparent to those with skill in the art so as not to obscure the description of embodiments of the disclosure. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the disclosure is defined only by the appended claims. 
     Information in the memory cells may decay over time. The memory cells may be refreshed on a row-by-row basis. During a refresh operation, the information in one or more rows may be read out and then written back to the respective rows. A refresh signal (such as auto-refresh signal AREF) may control a timing of the refresh operations. In some embodiments, the memory device may generate one or more “pumps”, which may be activations of an internal refresh signal responsive to receiving an activation of the refresh signal. The memory device may perform a refresh operation responsive to the pumps (and/or the refresh signal). The memory device may be perform more than one type of refresh operation, and at each pump may determine which type of refresh operation to perform and may refresh one or more wordlines based on the type of the refresh operation. 
     One type of refresh operation may be an auto-refresh operation. In an auto-refresh operation, the memory device may refresh a group of wordlines from a sequence of wordlines, and then during a next auto-refresh operation may refresh the next group of wordlines in the sequence. Over time, the memory device may carry out auto-refresh operations to cycle through the different rows of the memory in order to prevent data loss. In some embodiments, the memory device may refresh each row of the memory device, and may cycle through the rows with a timing based on a normal rate of data degradation in the memory cells (e.g., so that each row is refreshed more frequently than an expected time it would take for data loss in that row). 
     Another type of refresh operation may be a targeted refresh operations. Repeated access to a particular row of memory (which may generally be referred to as an aggressor row) may cause an increased rate of decay in neighboring rows (which may generally be referred to as victim rows) due, for example, to electromagnetic coupling between the rows. Information in the victim rows may decay at a rate such that data may be lost if they aren&#39;t refreshed before the next auto-refresh operation of that row. In order to prevent information from being lost, it may be necessary to identify aggressor rows and then carry out a targeted refresh operation where one or more associated victim rows can be refreshed. In some embodiments, the targeted refresh operation may “steal” a timeslot (e.g., an activation of a pump, an activation of the auto-refresh signal) which would have otherwise been used for an auto-refresh operation. 
     It may be important to control an amount of current drawn by the memory device during refresh operations. An auto-refresh operation may draw more current than a targeted refresh operation, since more rows may be refreshed during a given auto-refresh operation than are refreshed during a given targeted refresh operation. It may be desirable to control the timing of targeted refresh and auto-refresh operations in order to ‘average out’ the power drawn by a sequence of refresh operations. 
     The present disclosure is drawn to apparatuses, systems, and methods for distributed targeted refresh operations. Rather than perform a block of auto-refresh operations and a then a block of targeted refresh operations, a memory device may distribute targeted refresh operations so that there is a more even power load over time. In some embodiments, the memory device may provide activations of a refresh signal, and may perform a plurality of refresh operations responsive to each activation of the refresh signal. At least one of the plurality of refresh operations associated with each activation of the refresh signal may be a targeted refresh operation. In some embodiments, the number of targeted refresh operations may change between different activations of the refresh signal. 
     In some embodiments, the memory device may determine a first victim row and a second victim row associated with a given aggressor row. The memory device may refresh the first victim row, and may then perform at least one other refresh operation before refreshing the second victim row. In some embodiments, the first victim row may be refreshed responsive to a pump associated with a first refresh signal, while the second victim row may be refreshed responsive to a pump associated with a second refresh signal. In some embodiments, the memory device may perform one or more auto-refresh operations between targeted refresh operations. In some embodiments, there may be more than one type of targeted refresh operation, and the memory may perform one or more targeted refresh operations of a different type between targeted refresh operations of the first type. 
       FIG. 1  is a block diagram of a semiconductor device according to at least one embodiment of the disclosure. The semiconductor device  100  may be a semiconductor memory device, such as a DRAM device integrated on a single semiconductor chip. 
     The semiconductor device  100  includes a memory array  112 . In some embodiments, the memory array  112  may include of a plurality of memory banks. Each memory bank includes a plurality of word lines WL, a plurality of bit lines BL and /BL, and a plurality of memory cells MC arranged at intersections of the plurality of word lines WL and the plurality of bit lines BL and BL. The selection of the word line WL is performed by a row control  108  and the selection of the bit lines BL and /BL is performed by a column control  110 . The bit lines BL and BL are coupled to a respective sense amplifier (SAMP). Read data from the bit line BL or /BL is amplified by the sense amplifier SAMP  117 , and transferred to read/write amplifiers  120  over complementary local data lines (LIOT/B), transfer gate (TG)  118 , and complementary main data lines (MIOT/B). Conversely, write data outputted from the read/write amplifiers  120  is transferred to the sense amplifier  117  over the complementary main data lines MIOT/B, the transfer gate  118 , and the complementary local data lines LIOT/B, and written in the memory cell MC coupled to the bit line BL or BL. 
     The semiconductor device  100  may employ a plurality of external terminals that include command and address (C/A) terminals coupled to a command and address bus to receive commands and addresses, clock terminals to receive clocks CK and /CK, data terminals DQ to provide data, and power supply terminals to receive power supply potentials VDD, VSS, VDDQ, and VSSQ. 
     The clock terminals are supplied with external clocks CK and /CK that are provided to a clock input circuit  122 . The external clocks may be complementary. The clock input circuit  122  generates an internal clock ICLK based on the CK and /CK clocks. The ICLK clock is provided to the command control  106  and to an internal clock generator  124 . The internal clock generator  124  provides various internal clocks LCLK based on the ICLK clock. The LCLK clocks may be used for timing operation of various internal circuits. The internal data clocks LCLK are provided to the input/output circuit  126  to time operation of circuits included in the input/output circuit  126 , for example, to data receivers to time the receipt of write data. 
     The C/A terminals may be supplied with memory addresses. The memory addresses supplied to the C/A terminals are transferred, via a command/address input circuit  102 , to an address decoder  104 . The address decoder  104  receives the address and supplies a decoded row address XADD to the row control  108  and supplies a decoded column address YADD to the column control  110 . The address decoder  104  may also supply a decoded bank address BADD, which may indicate the bank of the memory array  118  containing the decoded row address XADD and column address YADD. The C/A terminals may be supplied with commands. Examples of commands include timing commands for controlling the timing of various operations, access commands for accessing the memory, such as read commands for performing read operations and write commands for performing write operations, as well as other commands and operations. The access commands may be associated with one or more row address XADD, column address YADD, and bank address BADD to indicate the memory cell(s) to be accessed. 
     The commands may be provided as internal command signals to a command control  106  via the command/address input circuit  102 . The command control  106  includes circuits to decode the internal command signals to generate various internal signals and commands for performing operations. For example, the command control  106  may provide a row command signal to select a word line and a column command signal to select a bit line. 
     The device  100  may receive an access command which is a row activation command ACT. When the row activation command ACT is received, a bank address BADD and a row address XADD are timely supplied with the row activation command ACT. 
     The device  100  may receive an access command which is a read command. When a read command is received, a bank address and a column address are timely supplied with the read command, read data is read from memory cells in the memory array  112  corresponding to the row address and column address. The read command is received by the command control  106 , which provides internal commands so that read data from the memory array  112  is provided to the read/write amplifiers  120 . The read data is output to outside from the data terminals DQ via the input/output circuit  126 . 
     The device  100  may receive an access command which is a write command. When the write command is received, a bank address and a column address are timely supplied with the write command, write data supplied to the data terminals DQ is written to a memory cells in the memory array  112  corresponding to the row address and column address. The write command is received by the command control  106 , which provides internal commands so that the write data is received by data receivers in the input/output circuit  126 . Write clocks may also be provided to the external clock terminals for timing the receipt of the write data by the data receivers of the input/output circuit  126 . The write data is supplied via the input/output circuit  126  to the read/write amplifiers  120 , and by the read/write amplifiers  120  to the memory array  112  to be written into the memory cell MC. 
     The device  100  may also receive commands causing it to carry out refresh operations. The refresh signal AREF may be a pulse signal which is activated when the command control  106  receives a signal which indicates a refresh mode. In some embodiments, the refresh command may be externally issued to the memory device  100 . In some embodiments, the refresh command may be periodically generated by a component of the device. In some embodiments, when an external signal indicates a refresh entry command, the refresh signal AREF may also be activated. The refresh signal AREF may be activated once immediately after command input, and thereafter may be cyclically activated at desired internal timing. Thus, refresh operations may continue automatically. A self-refresh exit command may cause the automatic activation of the refresh signal AREF to stop and return to an IDLE state. 
     The refresh signal AREF is supplied to the refresh control circuit  116 . The refresh control circuit  116  supplies a refresh row address RXADD to the row control  108 , which may refresh a wordline WL indicated by the refresh row address RXADD. The refresh control circuit  116  may control a timing of the refresh operation, and may generate and provide the refresh address RXADD. The refresh control circuit  116  may be controlled to change details of the refreshing address RXADD (e.g., how the refresh address is calculated, the timing of the refresh addresses), or may operate based on internal logic. 
     The refresh control circuit  116  may selectively output a targeted refresh address (e.g., a victim address) or automatic refresh addresses (auto-refresh address) as the refreshing address RXADD. The automatic refresh addresses may be a group of addresses from a sequence of addresses of the memory array  118 . The refresh control circuit  116  may cycle through the sequence of auto-refresh addresses at a rate determined by AREF. 
     The refresh control circuit  116  may also determine targeted refresh addresses which are addresses that require refreshing (e.g., victim addresses corresponding to victim rows) based on the access pattern of nearby addresses (e.g., aggressor addresses corresponding to aggressor rows) in the memory array  112 . The refresh control circuit  116  may selectively use one or more signals of the device  100  to calculate the targeted refresh address RXADD. For example, the refresh address RXADD may be a calculated based on the row addresses XADD provided by the address decoder. The refresh control circuit  116  may sample the current value of the row address XADD provided by the address decoder  104  and determine a targeted refresh address based on one or more of the sampled addresses. 
     The targeted refresh address may be based on characteristics over time of the row addresses XADD received from the address decoder  104 . The refresh control circuit  116  may sample the current row address XADD to determine its characteristics over time. The sampling may occur intermittently, with each sample acquired based on a random or semi-random timing. The refresh control circuit  116  may use different methods to calculate a targeted refresh address based on the sampled row address XADD. For example, the refresh control circuit  116  may determine if a given row is an aggressor address, and then calculate and provide addresses corresponding to victim addresses of the aggressor address as the targeted refresh address. In some embodiments, more than one victim address may correspond to a given aggressor address. In this case the refresh control circuit may queue up multiple targeted refresh addresses, and provide them sequentially when it determines that a targeted refresh address should be provided. The refresh control circuit  116  may provide the targeted refresh address right away, or may queue up the targeted refresh address to be provided at a later time (e.g., in the next time slot available for a targeted refresh). 
     The refresh address RXADD may be provided with a timing based on a timing of the refresh signal AREF. The refresh control circuit  116  may have time slots corresponding to the timing of AREF, and may provide one or more refresh addresses RXADD during each time slot. In some embodiments, the targeted refresh address may be issued in (e.g., “steal”) a time slot which would otherwise have been assigned to an auto-refresh address. In some embodiments, certain time slots may be reserved for targeted refresh addresses, and the refresh control circuit  116  may determine whether to provide a targeted refresh address, not provide an address during that time slot, or provide an auto-refresh address instead during the time slot. 
     For example, the refresh control circuit  116  may provide one or more refresh pump signals responsive to each activation of the refresh signal AREF. In some embodiments, the refresh control circuit  116  may provide a group of a set number of refresh pumps (e.g., activations of the refresh pump signal) for each activation of AREF. For example, the refresh control circuit  116  may provide five pumps for each activation of AREF, although more or less pumps may be used in other examples. Each pump may be associated with a refresh operation (e.g., either an auto-refresh operation or a targeted refresh operation) and the row control  108  may perform a refresh operation based on the refresh address RXADD each time the refresh pump signal is activated. In some embodiments, there may be a targeted refresh operation in each group of refresh pumps (e.g., there may be at least one targeted refresh operation responsive to each activation of AREF). In some embodiments, the number of targeted refresh operations may change between different groups of refresh pumps. For example, there may be different numbers of targeted refresh operations responsive to even and odd activations of AREF. 
     In some embodiments, the refresh control circuit  116  may perform more than one type of targeted refresh operation. The refresh control circuit  116  may use internal logic to determine when to perform the second type of targeted refresh operation. In some embodiments, the refresh control circuit  116  may count a number of activations of AREF, and may determine when to perform the second type of targeted refresh operation based on the count of AREF. For example, in some embodiments the refresh control circuit  116  may perform auto-refresh operations and the first and second type of targeted refresh operation for some number of activations of AREF (e.g., 4) and then may perform auto-refresh operations and the first type of targeted refresh operation for some number of activations of AREF (e.g., 8). 
     The power supply terminals are supplied with power supply potentials VDD and VSS. The power supply potentials VDD and VSS are supplied to an internal voltage generator circuit  128 . The internal voltage generator circuit  128  generates various internal potentials VPP, VOD, VARY, VPERI, and the like based on the power supply potentials VDD and VSS supplied to the power supply terminals. The internal potential VPP is mainly used in the row control  108 , the internal potentials VOD and VARY are mainly used in the sense amplifiers SAMP included in the memory army  112 , and the internal potential VPERI is used in many peripheral circuit blocks. 
     The power supply terminals are also supplied with power supply potentials VDDQ and VSSQ. The power supply potentials VDDQ and VSSQ are supplied to the input/output circuit  126 . The power supply potentials VDDQ and VSSQ supplied to the power supply terminals may be the same potentials as the power supply potentials VDD and VSS supplied to the power supply terminals in an embodiment of the disclosure. The power supply potentials VDDQ and VSSQ supplied to the power supply terminals may be different potentials from the power supply potentials VDD and VSS supplied to the power supply terminals in another embodiment of the disclosure. The power supply potentials VDDQ and VSSQ supplied to the power supply terminals are used for the input/output circuit  126  so that power supply noise generated by the input/output circuit  126  does not propagate to the other circuit blocks. 
       FIG. 2  is a block diagram of a refresh control circuit according to an embodiment of the present disclosure. In some embodiments, the refresh control circuit  200  may be used to implement the refresh control circuit  116  of  FIG. 1 . The refresh control circuit  200  may provide a refresh address RXADD to a row control (e.g., row control  108  of  FIG. 1 ). The refresh control circuit  200  may use internal logic to determine if the provided refresh address RXADD indicates a victim row associated with an aggressor row as part of a targeted refresh address or if the refresh address RXADD indicates a group of auto-refresh addresses as part of an auto-refresh operation. The refresh control circuit  200  may also identify aggressor rows and may control the timing of refresh operations based on the timing of the refresh signal AREF. 
     The refresh control circuit  200  represents a particular example embodiment. In the example of  FIG. 2 , the refresh control circuit  200  is capable of performing two different types of targeted refresh operations. In a first type of targeted refresh operations, a pair of victim rows are identified which are physically adjacent to the aggressor row. These victim rows may generally be referred to as +1 and −1 victim rows. In a second type of targeted refresh operation, the refresh control circuit  200  identifies a pair of victim rows which are adjacent to the adjacent rows, which may generally be referred to as +2 and −2 victim rows. Accordingly, the +1 row is between the aggressor row and the +2 row, and the −1 row is between the aggressor row and the −2 row. The refresh control circuit  200  also provides a plurality of “pumps” responsive to each activation of the refresh signal AREF. The pumps may control the timing of refresh operations, and a refresh address RXADD may be provided and refreshed with each pump. Other refresh control circuits in other embodiments may, for example, perform more or less types of targeted refresh operations, and/or may include targeted refresh operations where the victim rows have a different relationship to the aggressor row. 
     The refresh control circuit  200  includes an address sampler  234  which determines if a row address XADD is an aggressor address. The address sampler  234  may ‘sample’ the value of XADD responsive to a sampling signal provided by a sampling signal generator  232 . The sampling signal generator  232  may provide a sampling signal ArmSample with timing which may be based in part on an oscillator  230  and the ACT/PRE signal of the memory. The address sampler  234  provides an identified aggressor address to an address converter  238 , which determines victim rows based on the identified aggressor address and provides them to selector  250 . The refresh control circuit  200  also includes a pump generator  240 , which generates a number of pump signals responsive to the refresh signal REF and provides them to the row control (e.g., row control  108  of  FIG. 1 ) and to a pump counter  244  which counts the pumps and provides that count to a sequence generator  246 . The refresh signal REF is also provided to a command counter  242 , which provides a +2/−2 En signal to a sampler control circuit  236  and to the sequence generator  246  and a count value to the sequence generator  246 . Based on +2/−2 En, the count value and the count of pumps, the sequence generator  246  provides an internal refresh signal IREF, and a first and second steal command Steal(all) and Steal(+2/−2) respectively. The internal refresh command IREF is provided to a reference address generator  248  which provides auto-refresh addresses to the selector  250 . The sampler control circuit  236  provides the signal Steal out which causes the address sampler  234  to provide an aggressor address to the address converter  238 . The signal Steal out is provided based on the +2/−2 En signal, and the steal signals Steal(all) and Steal(+2/−2). The selector  250  provides the refresh address RXADD based on the steal signals Steal(all) and Steal(+2/−2). 
     The refresh control circuit  200  receives the row address XADD (e.g., from address decoder  104 ) and an activation and/or pre-charge signal ACT/PRE (e.g., from the command control  106 ). These may be used, in part, to determine if a given row specified by XADD is an aggressor row. The value of XADD may change over time as the memory performs operations (such as access operations) on different wordlines of the memory. The address sampler  234  may ‘sample’ a current value of the row address XADD when the sampling signal ArmSample is activated. Based on the values of one or more sampled address(es), the address sampler  234  may provide an aggressor address HitXADD to the address converter  238 . 
     The sampling signal generator  232  provides activations of the sampling signal ArmSample to the address sampler  234 . In some embodiments, the sampling signal generator  232  may provide the sampling signal ArmSample with regular timing. In some embodiments, the sampling signal generator  232  may provide activations of ArmSample with random, semi-random, and/or pseudo-random timing. In some embodiments, the timing at which ArmSample is provided may be influenced by one or more additional signals. For example, in the particular refresh control circuit  200  of  FIG. 2 , the sampling signal generator  232  may semi-randomly provide activations of ArmSample based on a timing signal provided by the oscillator  230  and the ACT/PRE signals. 
     In the example embodiment of  FIG. 2 , the address sampler  234  may be a content addressable memory (CAM) sampler, and may store a number of sampled addresses. As described in more detail in  FIG. 3 , when the address sampler  234  receives the signal Steal out from the sampler control circuit  236 , the address sampler  234  may provide an address as the aggressor address HitXADD. The address converter  238  may receive the aggressor address HitXADD and provide the addresses of victim rows associated with the provided aggressor address. The address converter  238  may determine the address of victim rows based on a physical relationship between the victim rows and the row associated with the aggressor address. In the embodiment of  FIG. 2 , the address converter provides two pairs of victim addresses, +1 and −1 which are adjacent to the aggressor row, and +2 and −2, which are adjacent to +1 and −1 respectively. 
     The pump generator  240  receives the refresh signal AREF, and provides a plurality of activations of a pump signal in response. For example, the pump generator  240  may provide five activations of the pump signal in response to each activation of AREF. More or less pumps may be provided in other examples. The activations of the pump signal are provided to the row control (e.g., row control  108  of  FIG. 1 ) and the row control may perform a refresh operation on the refresh address RXADD each time the pump signal is activated. Accordingly, responsive to each activation of AREF, a number (in this example, five) of refresh operations are performed. 
     The command counter  242  counts a number of activations of the refresh signal REF, while the pump counter  244  counts a number of activations of the refresh pump signal. The command counter  242  provides the signal +2/−2 En based on the number of activations of the refresh signal AREF. In some embodiments, +2/−2 En may be provided at an active level responsive to the first four activations of AREF out of a group of 16, or +2/−2 En may be provided as one shot pulse to control the first four activations of AREF out of a group of 16. Thus, +2/−2 En may be active for four activations of AREF and then inactive for twelve activations of AREF. The cycle may then repeat. Other timings of the activations of +2/−2 En may be used in other examples. 
     The pump counter  244  may count a number of activations of the refresh pump signal provided by the pump generator  240 , and may provide that count to the sequence generator  246 . Each time the pump signal is activated by the pump generator  240 , the pump counter  244  may increment a value of a pump count. In some embodiments, the pump counter  244  may provide a signal which indicates a value of the pump count to the sequence generator  246 . In some embodiments, the pump counter  244  may provide a signal which may be active when the pump count is at a certain value (or values). For example, the pump counter  244  may have a maximum value, and may reset to a minimum value and provide a signal when the maximum value is exceeded. 
     The sequence generator  246  determines if a given activation of the pump signal will be associated with an auto-refresh operation, a first type of targeted refresh operation (e.g., a +1/−1 operation), or a second type of targeted refresh operation (e.g., a +2/−2 operation). The sequence generator  246  receives the pump count from the pump counter  244  and the +2/−2 En signal from the command counter  242 . Based on the states of these inputs, the sequence generator  246  provides one or more signals which indicate a type of refresh operation that should be performed. The sequence generator  246  may provide the internal refresh signal IREF to indicate that an auto-refresh operation should be performed. The sequence generator  246  may provide the Steal (all) signal to indicate that a targeted refresh operation should be performed (e.g., either a first type of targeted refresh operation or a second type of targeted refresh operation). The sequence generator  246  may provide the Steal (+2/−2) signal to indicate that the second type of targeted refresh operation should be performed. Accordingly, the signals Steal (all) and Steal(+2/−2) both being active may indicate that the second type of targeted refresh operation should occur, while Steal (all) being active and Steal (+2/−2) being inactive may indicate that the first type of targeted refresh operation should occur. 
     The refresh address generator  248  provides an auto refresh address (or group of auto-refresh addresses) Ref_Add responsive to an activation of the internal refresh signal IREF. In some embodiments, Ref_Add may be a signal which represents a block of addresses to be refreshed. The refresh address generator  248  may have a sequence of memory addresses, and may provide a next group of addresses from the sequence each time the internal refresh signal IREF is activated. In some embodiments, the refresh address generator  248  may comprise a refresh address counter, and may count through a list of refresh addresses each time the signal IREF is activated. 
     The selector  250  provides either the auto-refresh address(es) Ref_Add, or one of the targeted refresh addresses +1, −1, +2, or −2 as the refresh address RXADD. The selector  260  provides an address based on the states of the signals Steal (all) and Steal (+2/−2). For example, if both Steal (all) and Steal (+2/−2) are inactive, the selector may provide the auto-refresh addresses Ref_Add as the refresh address RXADD, and an auto-refresh operation may be performed on the addresses indicated by Ref_Add. If Steal (all) is active but Steal (+2/−2) is inactive, the selector  250  may provide the +1 and −1 addresses as the refresh address RXADD a first type of targeted refresh operation may be performed on the addresses indicated by +1 and −1. In some embodiments, a first time that steal signals indicate the first type of targeted refresh operation, +1 may be provided as the refresh address RXADD, and a next time that the steal signals indicate the first type of targeted refresh operation, −1 may be provided as the refresh address RXADD. When both Steal (+2/−2) and Steal (all) are active, the second type of targeted refresh operation may be performed in a manner similar to the first type of targeted refresh operation. 
     The sampler control circuit  236  may provide the steal out signal to the address sampler  234  to indicate that that a new aggressor address HitXADD should be provided by the address sampler  234 . As described in more detail in  FIG. 3 , the address sampler  234  may store a plurality of potential aggressor addresses. Responsive to the signal Steal out, the address sampler  234  may provide one of the stored addresses as the aggressor address HitXADD, and the address converter  238  may determine the addresses +1, −1, +2, and −2 based on the provided aggressor address HitXADD. 
     The sampler control circuit  236  may provide the signal Flush after all victim addresses for a given identified aggressor address HitXADD have been refreshed. In some embodiments, the sampler control circuit  236  may provide the signal Flush responsive to the states of +2/−2 En, Steal (+2/−2), and Steal (all). In some embodiments, the signal +2/−2 En being in an active state may indicate that the second type (e.g., +2 and −2) of targeted refresh operation should be performed instead of the first type (e.g., +1 and −1) of targeted refresh operation. In some embodiments, the signal +2/−2 En being active may indicate that both the first type (e.g., +1 and −1) and the second type (e.g., +2 and −2) of targeted refresh operations should be performed on a given aggressor address. For example, when +2/−2 En is active, the signal Flush may be provided after each of +1, −1, +2, and −2 for a given aggressor address HitXADD have been provided by the selector  250  as the refresh address RXADD. For example, in some embodiments, when +2/−2 En is active, the signal Flush may be provided after four activations of Steal(all). In some embodiments, when +2/−2 En is active, the signal Flush may be provided upon a second activation of Steal (+2/−2) (e.g., on every other activation of Steal(+2/−2)). When the signal +2/−2 En is not active, the refresh control circuit  200  may only perform the first type of targeted refresh operation and so the signal Flush may be provided after both +1 and −1 for a given aggressor address HitXADD have been provided by the selector  250  as the refresh address RXADD. In some embodiments, when +2/−2 En is inactive, the sampler control circuit  236  may provide Flush after two activations of Steal(all). 
       FIG. 3  is a block diagram of an address sampler according to an embodiment of the present disclosure. In some embodiments, the address sampler  300  may be used to implement the address sampler  234  of  FIG. 2 . The particular embodiment of the address sampler  300  may be a content addressable memory (CAM) address sampler. The address sampler  300  may include a series of registers  352 , each of which may have a corresponding counter  354 . The counters  354  may be coupled to a comparator  356  which may be coupled to a pointer  362  through a counter scrambler  358 . The registers  352  may be coupled to an address latch  360 , which may store and provide an identified row hammer address as the match address HitXADD. 
     The address sampler  300  may sample a current row address XADD responsive to the sample signal ArmSample. The signal Steal out may cause the address sampler  300  to determine if a sampled address (e.g., an address stored in one of the registers  352 ) is a row hammer address and store it on the address latch  360 , where it can be provided to a refresh address generator (e.g., refresh address converter  238  of  FIG. 2 ) as the match address HitXADD. 
     Each time the sample signal ArmSample is provided, the current row address XADD may be compared to the registers  352 . If the current address XADD is already stored in one of the registers, then the counter  354  associated with that register  352  may be incremented. If the current address XADD is not already stored in one of the registers  352 , it may be added to the registers  352 . If there is an open register (e.g., a register without a latched address) then the sampled address XADD may be stored in the open register. If there is not an open register, then the register associated with the counter  354  which has the lowest value (as indicated by the pointer  362 ) may have its latched address replaced with the sampled address XADD. 
     The Steal out signal may cause the comparator  356  to determine a counter  354  with a maximum and minimum value. These may be provided to a counter scrambler  358 , which may match the maximum and minimum counter  354  to their respective associated registers  352 . The pointer  362  may point to the register  352  associated with the maximum value of count in the counters  354  and may point to the register  352  associated with the minimum value of count in the counters  354 . The minimum pointer may be used to overwrite a register  352  when a new address XADD is sampled and there is no open register  352  to store it in. The signal Flush may cause the counter  354  associated with the address currently stored in the latch  360  to be reset. The address stored in the address latch  360  may be provided as the match address HitXADD. 
       FIG. 4  shows a timing diagram of a refresh operations according to an embodiment of the present disclosure. The timing diagram  400  includes a portion  410 , shown in greater detail for ease of explanation. The first line of the timing diagram  400  shows a refresh signal AREF, which is periodically activated during a refresh mode of the memory device. Each block along the first line may represent an activation of AREF. In some embodiments, AREF may be a binary signal, and an activation may represent a period where the value of the signal is raised from a first logical level (e.g., a low logical level) to a second logical level (e.g., a high logical level). 
     The second line of the timing diagram  400  shows a refresh pump signal. The vertical lines of the refresh pump signal may represent an activation of the refresh pump signal (e.g., as provided by pump generator  240  of  FIG. 2 ). In some embodiments, the refresh pump signal may be a binary signal, and each activation may be a ‘pulse’ of the signal, where the signal is briefly changed to a different logical level (e.g., raised from a low logical level to a high logical level) and then returned to its original logical level (e.g., drops from a high logical level back to a low logical level). Each activation of the refresh signal AREF may be associated with a group of a number of activations of the refresh pump signal. As shown in the example embodiment of  FIG. 4 , there may be a group of five activations of the refresh pump signal for each activation of AREF. Each activation of the refresh pump may be associated with a refresh operation. The type of refresh operation may change (e.g., based on the signals provided by the sequence generator  246  of  FIG. 2 ) based on internal logic of a refresh control circuit (e.g., refresh control circuit  116  of  FIG. 1 and/or 200  of  FIG. 2 ). 
     At least one pump in each group of pumps may be associated with a targeted refresh operation. In other words, responsive to each activation of the refresh signal AREF, there may be at least one targeted refresh operation. In some embodiments, the targeted refresh operation may be at different times within the group of pumps responsive to different activations of the refresh signal AREF. For example, in the embodiment shown in  FIG. 4 , the targeted refresh operations are on different pumps in groups of pumps based on even and odd activations of the refresh signal AREF. 
     In the embodiment of  FIG. 4 , the memory device may perform an auto-refresh operation and one type of targeted refresh operation. In the targeted refresh operation of  FIG. 4 , the memory may refresh two different victim wordlines associated with a given aggressor wordline, which may be the wordlines which are adjacent to the aggressor wordline (e.g., +1 and −1). A portion  410  of the timing diagram  400  is shown with expanded timing to show how targeted refresh operations may be distributed throughout the auto-refresh operations. 
     The memory device may perform a targeted refresh operation on the second and fifth refresh pumps of a first refresh signal activation, and perform a targeted refresh operation on the third refresh pump of a second refresh signal activation. This cycle may then repeat such that even numbered activations of AREF (starting with ‘0’) have targeted refresh operations on the second and fifth pumps, while odd numbered activations of AREF have targeted refresh operations on the third pump. Accordingly, responsive to a first AREF, the memory may perform an auto-refresh operation, then a targeted refresh operation, then two auto-refresh operations, then a targeted refresh operation. Responsive to a next AREF, the memory may perform two auto-refresh operations, a targeted refresh operation, and then two auto-refresh operations. 
     In the embodiment of  FIG. 4 , the memory device may perform two targeted refresh operations on each identified aggressor address (e.g., one for the +1 address and one for the −1 address). The aggressor address may be referred to as a “seed,” and each seed may have some number of victim addresses associated with it. For example, a given seed may have two associated addresses (e.g., +1 and −1) for two targeted refresh operations. The first seed (Seed0) may have its associated victim addresses refreshed on the second and fifth pumps of the group of pumps associated with a first activation of the refresh signal. However, since there is only one targeted refresh operation during odd numbered activations of the refresh signal, the next seed (Seed1) may be split across the second and third activations of AREF. In particular the second seed (Seed1) may have a first victim address (e.g., +1) refresh on the third pump of the second group of pumps, and the second victim address (e.g., −1) may be refreshed on the second pump of the third group of pumps. The third seed (seed 2) may then begin on the fifth pump of the third group of pumps and finish on the third pump of the fourth group of pumps. The cycle may then repeat. 
     In this manner, a targeted refresh operations may be distributed throughout the refresh operations. Each group of pumps may include at least on targeted refresh operation. In the embodiment of  FIG. 4 , each targeted refresh operations may be separated by at least one auto-refresh operation. The pumps associated with the targeted refresh operation may change between different activations of AREF. For example, a targeted refresh operation may be separated from a next targeted refresh operation by either two or three auto-refresh operations. 
       FIG. 5  shows a timing diagram of refresh operations according to an embodiment of the present disclosure. The timing diagram  500  and portion  510  may generally be similar to the timing diagram of  FIG. 4 . However, in the embodiment of  FIG. 5 , the memory device may perform two different types of targeted refresh operations. In particular, the memory device may perform a second type of targeted refresh operation instead of the first type of targeted refresh operation during certain activations of the refresh signal AREF. 
     For the sake of brevity, operations and timing which are similar to those already described will not be repeated in regards to  FIG. 5 . The first line represents activations of the refresh signal AREF, while the second line represents refresh operations when the second type of targeted refresh operations are not enabled. The first and second line of the timing diagram  500  may generally be the same as the operations of the timing diagram  400  and portion  410  of  FIG. 4 . The third line of the timing diagram  500 , as well as the expanded portion  510 , represent a situation where the second type of targeted refresh operation are performed. 
     In the embodiment of  FIG. 5 , the memory device may perform the second type of targeted refresh operation instead of the first type of targeted refresh operation responsive to certain activations of AREF. In particular, the memory device may perform +2/−2 refresh operations responsive to the first four activations of AREF and then perform +1/−1 refresh operations responsive to the next twelve activations of AREF (e.g., by enabling +2/−2 En of  FIG. 2  for 4 out of 16 AREFs). 
     In some embodiments, the activations of AREF may be counted (e.g., by command counter  242 ) up to a maximum value of 8 (e.g., the counter may run from 0 to 7). In that case, the counter may activate the second type of targeted refresh operation (e.g., by providing +2/−2 En) on the first four counts of every other cycle of counts. 
     The portion  510  shows the refresh operations during the first four activations of a cycle of 16 activations of AREF, when the second type of targeted refresh operation is enabled. Responsive to these activations of AREF, the memory device may refresh the +2 and −2 addresses with the same timing as the refreshing of the +1 and −1 addresses discussed in regards to  FIG. 4 . Accordingly, the second type of targeted refresh operation may be performed on the second and fifth pumps of a first AREF, and the third pump of a second AREF. Once four AREFs worth of refresh operations have been performed (which may include +2 and −2 addresses associated with 3 different aggressor addresses (e.g., ‘seeds’)), the memory may go back to performing the first type of targeted refresh operation for the next twelve activations of AREF. 
       FIG. 6  shows a timing diagram of refresh operations according to an embodiment of the present disclosure. The timing diagram  600  and portion  610  may be generally similar to the timing diagram  400  and portion  410  of  FIG. 4  and the timing diagram  500  and portion  510  of  FIG. 5 . For the sake of brevity, features and operations previously described with not be repeated here.  FIG. 6  differs from  FIGS. 4 and 5  in that the timing diagram  600  shows an embodiment where the memory device performs the first type of targeted refresh operation and the second type of targeted refresh operation responsive to certain activations of AREF. 
     The first line of the timing diagram  600  shows activations of the refresh signal AREF. The second line shows refresh operations when the second type of targeted refresh operation is not enabled. The first two lines of the timing diagram  600  may generally be the same as the first two lines of the timing diagram  400  of  FIG. 4  and the timing diagram  500  of  FIG. 5 . Similar to the embodiment discussed in  FIG. 5 , in the timing diagram  600 , the third line (and the portion  610 ) represent refresh operations when the second type of targeted refresh operation is enabled. In the embodiment of  FIG. 5 , the first type of targeted refresh operation is replaced with the second type of targeted refresh operation, as previously described. However,  FIG. 6  represents an embodiment where, for the first four activations of AREF, refresh pumps are used for auto-refresh operations, the first type of targeted refresh operation and the second type of targeted refresh operation. 
     The inset portion  610  shows refresh operations performed responsive to a first four activations of AREF out of a cycle of 16. These first four activations of AREF are associated with pumps which are used to perform auto-refresh operations, and the first and second type of targeted refresh operation (e.g., +1, −1, +2, and −2). The memory device may perform targeted refresh operations responsive to the same pump activations as in the embodiments of  FIGS. 4 and 5 , and may also perform targeted refresh operations on additional pumps. Accordingly, the memory device may perform targeted refresh operations on the second and fifth pumps of a first AREF activation, and the third pump of a second AREF activation and also perform targeted refresh operations on the third pump of the first AREF activation and on the first and fourth pump of the second AREF activation. Overall, the memory device may perform targeted refresh operations on the second, third and fifth pumps responsive to a first activation of AREF, and on the first, third, and fourth pumps responsive to a second activation of AREF. 
     Since both the first and second type of targeted refresh operation are being performed, each aggressor address may have four different targeted refresh operations (e.g., one on +1, −1, +2, and −2). In other words, each seed may correspond to four targeted refresh operations. Over four different activations of AREF, the victim rows associated with three different seeds may be refreshed. The memory device may perform a targeted refresh on the +1 address responsive to a first time there is a first type of targeted refresh operation, and then refresh −1 on the second time there is the first type of targeted refresh operation. The +2 and −2 addresses may be refreshed in a similar manner. Thus, in the embodiment of  FIG. 6 , the +1, +2, −1, and −2 addresses may be refreshed in that order. Other timings may be used in other embodiments. 
     The first seed (seed0) may be associated with targeted refresh operations on the second, third, and fifth pumps responsive to a first AREF activation, and a first pump responsive to a next activation of AREF. The second seed (seed1) may be associated with targeted refresh operations on the third and fourth pumps of the second AREF activation, and the second and third pumps of a third AREF activation. The third seed (seed2) may be associated with targeted refresh operations on the fifth pump of the third AREF activation, and the first, third, and fourth pump of a fourth AREF activation. 
       FIG. 7  shows a timing diagram of internal signals of a refresh control circuit according to an embodiment of the present disclosure. The timing diagram  700  represents the internal signals of a refresh control circuit (e.g., the refresh control circuit  200  of  FIG. 2 ) while performing refresh operations in a manner similar to the timing diagram  600  of  FIG. 6 . 
     The first line of the timing diagram  700  represents the refresh pump signal (e.g., as provided by the pump generator  240  of  FIG. 2 ). The pump signal is activated five times in response to each activation of the refresh signal AREF (not shown). The second line of the timing diagram  700  shows the +2/−2 En signal (e.g., as provided by the command counter  242  of  FIG. 2 ). The +2/−2 En signal may be at a high logical level to indicate that the second type of targeted refresh operation (e.g., refreshing the +2 and −2 addresses) should be performed. The signal +2/−2 En may be at a high logical level for the first four groups of pumps (e.g., the first four activations of AREF) and may then return to a low logical level for the next eight groups of pumps. Accordingly, both +1/−1 and +2/−2 targeted refresh operations may be performed during the first four groups of pumps. 
     The third, fourth, and fifth lines of the timing diagram  700  show the signals Steal(all), Steal(+2/−2), and IREF respectively. These signals may be provided by a sequence generator (e.g., sequence generator  246 ) and may determine if a given activation of the refresh pump signal is used for an auto-refresh operation, a first type of targeted refresh operation (e.g., +1 and −1) or a second type of targeted refresh operation (e.g., +2 and −2). When IREF is active, neither Steal(all) nor Steal(+2/−2) are active, the memory device may perform an auto-refresh operation. Steal(all) may be provided when any type of targeted refresh operation is performed, while Steal(+2/−2) may be provided to indicate that the second type of targeted refresh operation should be performed. 
     Accordingly, at a first pump, only IREF is active, and thus an auto-refresh operation may be associated with the first pump. At a second pump, only Steal(all) is active, and the first type of targeted refresh operation may be performed. At the third pump, both Steal(all) and Steal(+2/−2) are active, so the second type of targeted refresh operation may be performed. At the fourth pump, IREF is active again, so another auto-refresh operation may be performed. At the fifth pump, only Steal(all) is active, so the first type of targeted refresh operation may be performed. In this manner, the sequence generator may distribute the different types of targeted refresh operation by selectively providing IREF, Steal(all), and Steal(+2/−2) each time the pump signal is provided. 
     The sixth line of the timing diagram  700  shows the signal Flush, which may be provided by a sampler control circuit (e.g., sampler control circuit  236  of  FIG. 2 ) to indicate that targeted refresh operations for a given aggressor address have been completed and that a new aggressor address should be provided (e.g., by address sampler  234 ). While +2/−2 En is active, Flush may be provided each fourth activation of Steal(all)(or each second activation of Steal(+2/−2)). When +2/−2 En is not active, Flush may be provided every other time that Steal(all) is provided. 
     Of course, it is to be appreciated that any one of the examples, embodiments or processes described herein may be combined with one or more other examples, embodiments and/or processes or be separated and/or performed amongst separate devices or device portions in accordance with the present systems, devices and methods. For instance, in each of embodiments shown in  FIGS. 4, 5 and 6 , one refresh signal always causes at least one targeted refresh operation. In some embodiments, one refresh signal may not always cause at least one targeted refresh operation. 
     Finally, the above-discussion is intended to be merely illustrative of the present system and should not be construed as limiting the appended claims to any particular embodiment or group of embodiments. Thus, while the present system has been described in particular detail with reference to exemplary embodiments, it should also be appreciated that numerous modifications and alternative embodiments may be devised by those having ordinary skill in the art without departing from the broader and intended spirit and scope of the present system as set forth in the claims that follow. Accordingly, the specification and drawings are to be regarded in an illustrative manner and are not intended to limit the scope of the appended claims.