Patent Publication Number: US-7911862-B2

Title: Latency control circuit and method thereof and an auto-precharge control circuit and method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 11/594,807, filed Nov. 9, 2006 (now U.S. Pat. No. 7,609,584), which claims priority to Korean Patent Application No. 10-2005-0111027, filed on Nov. 19, 2005, Korean Patent Application No. 10-2006-0039897, filed on May 3, 2006, and Korean Patent Application No. 10-2006-0063463, filed on Jul. 6, 2006, in the Korean Intellectual Property Office. The contents of all of the above applications are incorporated herein in their entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments of the present invention relate generally to a latency control circuit and method thereof and an auto-precharge control circuit, and more particularly to a latency controlling circuit and a method of controlling latency and an auto-precharge control circuit. 
     2. Description of the Related Art 
     Data may be input to and/or output from a synchronous semiconductor device in synchronization with an external clock signal. Double data rate (DDR) dynamic random access memory (DRAM) may use a write latency (WL) scheme and/or an additive latency (AL) scheme to increase an efficiency of an address bus line or a command bus line. 
     If the latency scheme is used, after a number of clock cycles corresponding to latency have been counted, in response to a command received from a controller (e.g., a read or write command), an address signal may be activated for designating a memory address to/from which an internal command signal and/or data may be input/output. A circuit for delaying an external address signal or command signal by WL, AL, or (WL+AL) may further be included. 
       FIG. 24  is a circuit diagram illustrating a conventional latency control circuit  1500 . Referring to  FIG. 24 , the conventional latency control circuit  1500  may include a plurality of registers  1511  through  1517  and a plurality of multiplexers  1521  through  1527 , which may be connected to each other in series. A WL signal WLi (e.g., where I=1˜M) may be based on WL. For example, if WL is set to 7, only a signal WL 7  may be activated (e.g., set to a first logic level, such as a higher logic level or logic “1”) and the remaining signals WLi, where I=1, 2, 3, 4, 5, 6, may be deactivated (e.g., set to a second logic level, such as a lower logic level or logic “0”). Accordingly, if the WL is 7, an address signal Ai may pass through the 7 registers  1511  through  1517  and then may be output as a delayed address signal CAi. Alternatively, if the WL is 4, the address signal Ai may pass through 4 registers  1511  through  1514  and then may be output as a delayed address signal CAi, and so on. Accordingly, after input latency (WL+AL), which may be caused due to an external command (e.g., a write command), a column address CAi for activating a column selection line may be generated. Therefore, a number of registers may be at least equal to the number of input latencies (AL+WL) for each bit of the address signal Ai. In an example, each register may be implemented by a flip-flop. Thus, a number of flip-flops may equal the number of input latencies within a circuit generating a bit of an address signal so that the circuit may be synchronized with an internal clock signal PCLK and may delay the address signals by desired latencies, thereby generating the column address CAi. 
     Because many flip-flops may be included in the conventional latency control circuit  1500 , a current consumption may be relatively large. In addition, a higher proportion of an available layout area may be reserved for the flip-flops within the conventional latency control circuit  1500 . 
     With increases in operating frequencies (e.g., above 800 MHz in DDR-DRAM), AL and WL may increase to 10 or more. As a result, a number of registers required to perform latency control on an address and/or a command may likewise increase. For example, if AL is 8 and WL is 10 in a 512 Megabyte (MB) DDR synchronous DRAM (SDRAM), 18 registers (i.e., 8 registers for AL and 10 registers for WL) may be required for each bit of a 16-bit address signal. In addition, 8 registers for AL may be required for each command. Thus, if a total of 5 commands (e.g., /WE, /CS, /RAS, /CAS, and /OE) are externally received, a number of registers required for latency control on addresses and commands may be expressed by 18*16+8*5=248. If the number of registers increases above a threshold (e.g., 200 registers), an area occupied by the registers may increase and routing may become increasingly complicated. Further, the number of registers may further increase to accommodate for burst length. The burst length may refer to a number of bits which may be consecutively input or output per data input/output pin in response to a write or read command. In a conventional memory device (e.g., DDR2), in which two bits of data may be input or output per data input/output pin during a single clock cycle, an address may be delayed by a clock cycle corresponding to “burst length/2”, and therefore, at least a number of registers corresponding to the “burst length/2” may be required to output the single address signal. Accordingly, as the size of latency control circuit  1500  increases, a line or conductive path of a clock signal input to the latency control circuit  1500  may become longer, thereby increasing a delay time of the clock signal. 
     In order to quickly perform write and/or read operations, a semiconductor memory device, and particularly, a DRAM device, may perform a precharge operation for charging bit lines to a given voltage level to close an activated bank. The activated bank may be precharged before a new row in the activated bank may be opened. In other words, if data is written to or read from a memory cell through a bit line, the electric potential of the bit line may be changed. Accordingly, it may be necessary to precharge the bit line to the given voltage level after the data write or read operation. 
     A conventional precharge operation may be performed using a precharge command or an auto-precharge function. A precharge operation may also be performed after a write operation using a precharge command or an auto-precharge function. If the precharge command is issued after a write command to perform the precharge operation, a transmission efficiency of a data bus line may be decreased because an idle section (e.g., a portion on which no data may be transmitted through a bus line within a system) may occur. Accordingly, the auto-precharge function may typically be used to perform the precharge operation. 
     Typically, a write auto-precharge function may be performed in response to a write auto-precharge command, which may be defined by making a given signal (e.g., a bit A 10  in an address signal), which may be input along with a write command applied from an external source (e.g., a memory controller), transition to the first logic level (e.g., a higher logic level or logic “1”). 
     Thus, if the given signal (e.g., the bit A 10  in the address signal) is set to the first logic level and received along with the write command, DRAM may internally generate a write auto-precharge command and may perform a write auto-precharge operation. The write command may be first executed based on the generated write auto-precharge command. The precharge operation may not be performed until the last data in a burst write sequence is stored in a memory array in response to the write command. After a given period of time following the last data being stored in the memory array, the precharge operation may be performed. 
     The given period of time may be a write recovery time tWR (e.g., a minimum “wait time” before data may be written to the memory cell). In an example, the write recovery time tWR may be fixed at about 15 ns. Accordingly, the precharge operation may be performed after the write recovery time tWR. The write auto-precharge command may thereby have to be delayed. 
       FIG. 25  illustrates a conventional auto-precharge control circuit  2100  which delays a write auto-precharge command by the write recovery time tWR. 
     Referring to  FIG. 25 , the auto-precharge control circuit  2100  may be a circuit for controlling an auto-precharge operation of DDR3 DRAM, which may include 8 banks and may have an operating frequency of 1.6 GHz. Accordingly, because a clock signal applied to the DDR3 DRAM may have a frequency of 800 GHz and a cycle of 1.25 ns, an auto-precharge command may be delayed by 12 clock cycles of the clock signal, which may correspond to 15 ns of the write recovery time tWR. 
     Referring to  FIG. 25 , the auto-precharge control circuit  2100  may include a precharge sub-signal generator  2110  and a precharge main signal generator  2120 . The precharge sub-signal generator  2110  may include a decoder  2111  and an AND element array  2112 . The decoder  2111  may output first precharge sub-signals BANK 0  through BANK 7 , which may respectively correspond to 8 banks, based on bank address signals dBA 0  through dBA 2 . The AND element array  2112  may include 8 AND elements connected in parallel and may perform an AND operation on each of the first precharge sub-signals BANK 0  through BANK 7  and a write auto-precharge command signal dWAP to output second precharge sub-signals FAP 0  through FAP 7 . 
     Referring to  FIG. 25 , the precharge main signal generator  2120  may include a plurality of register arrays, which may respectively delay the second precharge sub-signals FAP 0  through FAP 7  output from the precharge sub-signal generator  2110  and may output precharge main signals PAPB 0  through PAPB 7  to the banks, respectively. The precharge operation may be performed based on the precharge main signals PAPB 0  through PAPB 7 . 
     Referring to  FIG. 25 , in order to delay the second precharge sub-signals FAP 0  through FAP 7  by the write recovery time tWR, each of the register arrays may include 12 registers connected in series, which may respond to an internal clock signal PCLK. 
     Accordingly, referring to  FIG. 25 , the number of registers included within the auto-precharge control circuit  2100  may be 96, which may be obtained by multiplying the number of banks (i.e., 8) by the number of clock cycles of the internal clock signal PCLK (i.e., 12) corresponding to the write recovery time tWR (e.g., 15 ns). As described above, the number of registers may be related to the number of banks and the cycle of a clock signal. With the increase of an operating frequency and the decrease of a cycle of a clock signal in a memory device, the number of clock cycles of the internal clock signal PCLK, which corresponds to the write recovery time tWR, may be increased. As a result, the number of registers required to execute a write auto-precharge command may be increased. 
     As the number of registers is increased, as well as an area occupied by the registers in a layout, loading of the internal clock signal PCLK, which may be input to each register, may also be increased. As a result, a power consumption or current consumption may be increased. 
     SUMMARY OF THE INVENTION 
     An example embodiment of the present invention is directed to a latency control circuit, including a master unit activating at least one master signal based on a reference signal and an internal clock signal and a plurality of slave units receiving the at least one master signal and a plurality of signals, each of the plurality of slave units outputting an output signal based at least in part upon one of the received plurality of signals. 
     Another example embodiment of the present invention is directed to a method of controlling latency, including receiving at least one master signal, the received at least one master signal activated based on a reference signal and an internal clock signal and receiving a plurality of signals and outputting an output signal based at least in part upon one of the received plurality of signals and latency information. 
     Another example embodiment of the present invention is directed to an auto-precharge control circuit, including a precharge command delay unit generating a plurality of first precharge command delay signals in response to an internal clock signal and a write auto-precharge command signal, at least one bank address delay unit outputting a delayed bank address signal and a precharge main signal generator outputting a precharge main signal to banks based on the delayed bank address signal 
     Another example embodiment of the present invention is directed to a latency control circuit and method for reducing a number of registers controlling latency, thereby decreasing routing complexity, a circuit area and delay of a clock signal. 
     Another example embodiment of the present invention is directed to a semiconductor memory device using the latency control circuit and a method of operating the semiconductor memory device. 
     Another example embodiment of the present invention is directed to an auto-precharge control circuit for reducing the number of registers to decrease an area occupied by the registers in a layout and to decrease loading of an internal clock signal, thereby reducing current consumption, and a semiconductor memory device including the same. 
     Another example embodiment of the present invention is directed to a method of controlling a precharging operation with an auto-precharge control circuit, including delaying a bank address signal based on a minimum time interval between executed memory commands and outputting a precharge main signal to one or more memory banks based on the delayed bank address signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate example embodiments of the present invention and, together with the description, serve to explain principles of the present invention. 
         FIG. 1  is a block diagram of a semiconductor memory device according to an example embodiment of the present invention. 
         FIG. 2  is a block diagram of the latency control circuit according to another example embodiment of the present invention. 
         FIG. 3  is a circuit diagram of a master unit according to another example embodiment of the present invention. 
         FIG. 4  is a circuit diagram of slave units according to another example embodiment of the present invention. 
         FIG. 5A  is a signal timing chart illustrating an operation of the latency control circuit of  FIG. 2  when the WL is 6 according to another example embodiment of the present invention. 
         FIG. 5B  is a signal timing chart illustrating an operation of the latency control circuit of  FIG. 2  when the WL is 4 according to another example embodiment of the present invention. 
         FIGS. 6 and 7  are circuit diagrams illustrating a master unit and a slave unit, respectively, according to another example embodiment of the present invention. 
         FIG. 8  is a block diagram of another latency control circuit according to another example embodiment of the present invention. 
         FIG. 9  is a circuit diagram of the master unit of  FIG. 8  according to another example embodiment of the present invention. 
         FIG. 10  is a circuit diagram of a slave unit according to another example embodiment of the present invention. 
         FIG. 11  is a signal timing chart illustrating an operation of the latency control circuit of  FIG. 8  when the WL is 9 according to another example embodiment of the present invention. 
         FIG. 12  is a block diagram of a command detection circuit according to another example embodiment of the present invention. 
         FIG. 13  is a block diagram of a command detection circuit according to another example embodiment of the present invention. 
         FIG. 14  is a block diagram of another latency control circuit according to another example embodiment of the present invention. 
         FIG. 15  is a block diagram of another latency control circuit according to another example embodiment of the present invention. 
         FIG. 16A  is a signal timing chart illustrating an operation of the latency control circuit of  FIG. 15  when the WL is 7 and the BL is 4, according to another example embodiment of the present invention. 
         FIG. 16B  is a signal timing chart illustrating an operation of the latency control circuit of  FIG. 15  when the WL is 1 and the BL is 4 according to another example embodiment of the present invention. 
         FIGS. 17A and 17B  are circuit diagrams of respective flip-flops according to another example embodiment of the present invention. 
         FIG. 18  is a block diagram of a semiconductor memory device according to another example embodiment of the present invention. 
         FIG. 19  is a block diagram of an auto-precharge control circuit according to another example embodiment of the present invention. 
         FIG. 20  is a circuit diagram of a precharge command delay unit according to another example embodiment of the present invention. 
         FIG. 21  is a circuit diagram of a bank address delay unit according to another example embodiment of the present invention. 
         FIG. 22  is a circuit diagram of a precharge main signal generator according to another example embodiment of the present invention. 
         FIG. 23  is a signal timing chart illustrating an operation of an auto-precharge control circuit according to another example embodiment of the present invention. 
         FIG. 24  is a circuit diagram illustrating a conventional latency control circuit. 
         FIG. 25  illustrates a conventional auto-precharge control circuit which delays a write auto-precharge command by a write recovery time tWR. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE PRESENT INVENTION 
     Detailed illustrative example embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. Example embodiments of the present invention may, however, be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein. 
     Accordingly, while example embodiments of the invention are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments of the invention to the particular forms disclosed, but conversely, example embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like numbers may refer to like elements throughout the description of the figures. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Conversely, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG. 1  is a block diagram of a semiconductor memory device  100  according to an example embodiment of the present invention. In the example embodiment of  FIG. 1 , the semiconductor memory device  100  may include a memory cell array  110 , an address buffer  120 , a row decoder  130 , a column decoder  140 , a bank decoder  145 , a data input circuit  150 , a data output circuit  160 , a clock circuit  170 , a command detection circuit  180 , a Mode Register Set/Extended Mode Register Set (MRS/EMRS) circuit  190  and a latency control circuit  200 . 
     In the example embodiment of  FIG. 1 , the memory cell array  110  may be a data storage in which numerous memory cells may be arranged in rows and columns. Input data IDATA input through the data input circuit  150  may be written to the memory cell array  110  based on an address signal ADDI. Output data ODATA read from the memory cell array  110  based on the address signal ADDI may be output through the data output circuit  160  to an external entity. To designate a memory cell to or from which data may be written or read, the address signal ADDI may be input to the address buffer  120 . The address buffer  120  may temporarily store the address signal ADDI input from the external entity. The row decoder  130  may receive the address signal ADD output from the address buffer  120  and may decode the address signal ADD into a row address of the memory cell array  110 . The column decoder  140  may receive a column address signal CA output from the latency control circuit  200  and may decode the column address signal CA into a column address of the memory cell array  110 . The bank decoder  145  may receive a bank address signal BAL output from the latency control circuit  200  and may decode the bank address signal BAL into a bank address designating a memory bank. The memory cell array  110  may read data from or may write data into a memory cell designated by the row address and the column address in a memory bank designated by the bank address. 
     In the example embodiment of  FIG. 1 , the clock circuit  170  may receive an external clock signal ECLK and may generate an internal clock signal PCLK from the external clock signal ECLK. In an example, the internal clock signal PCLK may be obtained by buffering the external clock signal ECLK. 
     In the example embodiment of  FIG. 1 , the command detection circuit  180  may receive a command signal CMD (e.g., /WE, /CS, /RAS, /CAS, etc.) from an external entity and may decode the command signal CMD to output a decoded command signal (e.g., a write command signal PWA). Although not shown in the example embodiment of  FIG. 1 , the command detection circuit  180  may further include a command buffer and a command decoder. In another example, the command detection circuit  180  may further include a latency control circuit in order to delay the command signal CMD by a number of clock cycles corresponding to an additive latency (AL). The decoded command signal (e.g., the write command signal PWA) may be output from the command detection circuit  180 . 
     In the example embodiment of  FIG. 1 , the MRS/EMRS circuit  190  may set an internal mode register in response to an MRS/EMRS command MRS_CMD and/or the address signal ADD for designating an operating mode of the semiconductor memory device  100 . Input latency (e.g., write latency (WL), AL, etc.) may be set by the MRS/EMRS command MRS_CMD in the mode register. The MRS/EMRS circuit  190  may output a WL signal WLi (e.g., wherein “i” may be a positive integer) based on WL information and may output an AL signal ALj (e.g., wherein “j” may be a positive integer) based on AL information. 
     In the example embodiment of  FIG. 1 , the latency control circuit  200  may receive the WL signal WLi from the MRS/EMRS circuit  190  and the address signal ADD from the address buffer  120  and may control the column address signal CA and the bank address signal BAL so as to be generated at a given time (e.g., after a given delay period) based on the WL signal WLi. The latency control circuit  200  may further receive the AL signal ALj from the MRS/EMRS circuit  190  and may control a given time when the column address signal CA and the bank address signal BAL are generated based on the WL signal WLi and the AL signal ALj. 
       FIG. 2  is a block diagram of the latency control circuit  200  according to another example embodiment of the present invention. In the example embodiment of  FIGS. 1 and 2 , the latency control circuit  200  may include a master unit  210  and a plurality of slave units  220 ,  221 ,  22   n  and  230 . The latency control circuit  200  may control a time at which the column address signal CA and the bank address signal BAL may be generated based on latency information, such as the WL signal WLi. Thus, in an example, the latency control circuit  200  may delay an address signal by a number of clock cycles corresponding to the latency information based on when the write command signal PWA is activated to control a generation time or activation time of a column address and a bank address. 
     In the example embodiment of  FIG. 2 , the master unit  210  may generate master signals PWA_WL 5 , PWA_WL 1  and PWL_BL in response to the internal clock signal PCLK, the write command signal PWA and the WL signal WLi. The write command signal PWA may be generated by the command detection circuit  180  in response to an external write command. 
       FIG. 3  is a circuit diagram of the master unit  210  of  FIG. 2  according to another example embodiment of the present invention. In the example embodiment of  FIG. 3 , the master unit  210  may include a write master signal generator  310  and a burst master signal generator  330 . 
     In the example embodiment of  FIG. 3 , the write master signal generator  310  may include a plurality of registers  311  through  317  and a plurality of multiplexers  321  through  327 , which may be connected in cascade or series. In an example, each of the registers  311  through  317  may be implemented by a flip-flop. The number of flip-flops included in the write master signal generator  310  may be determined by a maximum value of the WL. For example, if the maximum value of the WL is M, where M may equal a natural number (e.g., a positive integer greater than or equal to 1), the write master signal generator  310  may include M flip-flops. As described hereinafter, for purposes of description, within the example embodiment of  FIG. 3 , it may be assumed that the maximum value of the WL may equal 7 (e.g., M=7) and a burst length may have a value of 8. However, it is understood that other example embodiments may include a maximum value of the WL other than 7. 
     In the example embodiment of  FIG. 3 , the internal clock signal PCLK may be input through a clock terminal CK into each of the flip-flops  311  through  317 . Each of the multiplexers  321  through  326  may select and output one of an output signal of a preceding flip-flop and the write command signal PWA in response to the corresponding WL signal WLi (e.g., wherein I=1 through M), which may be output from the MRS/EMRS circuit  190  based on WL. For example, if WL equals 7, a WL signal WL 7  may be activated (e.g., set to the first logic level, such as a higher logic level or logic “1”) and the remaining signals WLi (i=1, 2, 3, 4, 5, 6) may be deactivated (e.g., set to the second logic level, such as a lower logic level or logic “0”). 
     In the example embodiment of  FIG. 3 , each of the first through sixth multiplexers  321  through  326  may select and output the write command signal PWA if the corresponding WL signal WLi (e.g., i=1˜6) is activated and may alternatively select and output an output signal of the preceding flip-flop if the corresponding WL signal WLi (i=1˜6) is deactivated. The seventh multiplexer  327  may select and output the write command signal PWA if the corresponding WL signal WL 7  is activated and may alternatively output the second logic level (e.g., a lower logic level or logic “0”) if the WL signal WL 7  is deactivated. 
     In the example embodiment of  FIG. 3 , each of the flip-flops  311  through  317  may output an input signal in synchronization with the internal clock signal PCLK. For example, an output signal of the first flip-flop  311  may be referred to as a first write master signal PWA_WL 1  and an output signal of the fifth flip-flop  315  may be referred to as a second write master signal PWA_WL 5 , and so on. 
     In the example embodiment of  FIG. 3 , the write master signal generator  310  may delay the write command signal PWA by a given delay period (e.g., an integer multiple of the internal clock signal PCLK in integer multiples of single clock cycle of the internal clock signal PCLK) and may output a given signal among delayed signals as the write master signal PWA_WL 1  or PWA_WL 5 . The write master signals PWA_WL 1  and PWA_WL 5  may have an interval of tCCD therebetween. In an example, the tCCD may be a CAS to CAS command delay and may be indicative of a minimum interval between commands in the number of clock cycles tCK. In an example, the CAS to CAS command delay tCCD may be determined before semiconductor devices are manufactured and may be equal to (BL/2), where BL is a burst length. The single clock cycle tCK may be used as a unit indicating a number of clock cycles in the internal clock signal PCLK. In other words, 1 tCK may indicate one clock cycle of the internal clock signal PCLK. 
     In the example embodiment of  FIG. 3 , if the WL is 7, the write command signal PWA may be input into the seventh flip-flop  317  as an input signal and may thereafter sequentially pass through the sixth, fifth, fourth, third, second, and first flip-flops  316 ,  315 ,  314 ,  313 ,  312 ,  312 , and  313 , respectively. As a result, the write command signal PWA may be delayed by about 3 tCK, thereby generating the second write master signal PWA_WL 5 , and the write command signal PWA may be delayed by the number of clock cycles corresponding to the WL (e.g., 7 tCK or clock cycles), thereby generating the first write master signal PWA_WL 1 . 
     In the example embodiment of  FIG. 3 , if the WL is 6, the write command signal PWA may be input into the sixth flip-flop  316  as an input signal and may thereafter sequentially pass through the fifth, fourth, third, second, and first flip-flops  315 ,  314 ,  313 ,  312 ,  312 , and  313 , respectively. As a result, the write command signal PWA may be delayed by about 2 tCK or clock cycles, thereby generating the second write master signal PWA_WL 5 , and the write command signal PWA may be delayed by the number of clock cycles corresponding to the WL (e.g., 6 tCK or clock cycles), thereby generating the first write master signal PWA_WL 1 . 
     In the example embodiment of  FIG. 3 , if the WL is set to another value (e.g., 5, 4, 3, 2, or 1, a value other than 6 or 7, etc.), the write master signal generator  310  may operate in the same manner as above described with respect to when WL equals 7 or 6. However, if the WL is 4, 3, 2, or 1, because the write command signal PWA is input into the fourth, third, second, or first flip-flop  314 ,  313 ,  312 , or  311 , the second write master signal PWA_WL 5  may not be generated, or activated (e.g., set to the first logic level, such as a higher logic level or logic “1”), but rather only the first write master signal PWA_WL 1  may be generated, or activated. 
     In the example embodiment of  FIG. 3 , the burst master signal generator  330  may include one or more registers  331  through  334 . In an example, the registers  331  through  334  may be implemented by flip-flops. The number of flip-flops included in the burst master signal generator  330  may be determined by the burst length (BL). In an example, the number of flip-flops may be (BL/2). In another example, BL may equal 8, and therefore, the number of flip-flops included in the burst master signal generator  330  may be 4 (e.g., because 8/2=4). Thus, the registers  331  through  334  may be referred to as eighth through eleventh flip-flops  331  through  334 . The internal clock signal PCLK may be input through a clock terminal CK into each of the eighth through eleventh flip-flops  331  through  334 . 
     In the example embodiment of  FIG. 3 , the eighth through eleventh flip-flops  331  through  334  may be connected in series and each may receive an output signal of a previous or preceding flip-flop. Thus, the eighth flip-flop  331  may receive an output signal of the first flip-flop  311  (e.g., the first write master signal PWA_WL 1 ). Likewise, the ninth flip-flop  332  may receive an output signal of the eighth flip-flop  331 , the tenth flip-flop  333  may receive an output signal of the ninth flip-flop  332 , the eleventh flip-flop  334  may receive an output signal of the tenth flip-flop  333 , and so on. In an example, an output signal of the eleventh flip-flop  334  may be output as a burst master signal PWA_BL. 
     In the example embodiment of  FIG. 3 , the burst master signal generator  330  may delay a final output signal of the write master signal generator  310  (e.g., the first write master signal PWA_WL 1 ) by a number of clock cycles equal to (BL/2), thereby outputting the burst master signal PWA_BL. Consequently, the burst master signal generator  330  may further delay by (BL/2) the write command signal PWA that has been delayed by the WL. 
       FIG. 4  is a circuit diagram of the slave units  22   i  and  230  of  FIG. 2  according to another example embodiment of the present invention. In an example, the slave unit  22   i  may be representative of any number of slave units, wherein i may equal 0, 1, . . . , n. Thus, while  FIG. 4  illustrates only the slave unit  22   i  for a column address signal and the slave unit  230  for a bank address signal, additional slave units may be added as the number of bits in the column address signal and/or the bank address signal increases. The address signal ADD may include a column address signal A and a bank address signal BA. 
     In the example embodiment of  FIG. 4 , the column address signal A and the bank address signal BA may be output signals of the address buffer  120  shown in  FIG. 1 , or alternatively, may be signals obtained by latching, sampling and/or delaying the output signals of the address buffer  120 . 
     In the example embodiment of  FIG. 4 , a suffix “i” or numeral added to an address signal A, BA, CA, or BAL may denote a particular bit within the address signal. While the example embodiment of  FIG. 4  illustrates one-bit bank address signal BA 0 , it is understood that a bank address signal may include a plurality of bits in other example embodiments of the present invention. Accordingly, a total number of slave units may be the sum of the number of bits in a column address and the number of bits in a bank address. 
     In the example embodiment of  FIG. 4 , each of the slave units  22   i  and  230  may generate a delay address bit signal corresponding to one “random” bit (e.g., any one of the bits) in the address signal in response to a plurality of master signals (e.g., three master signals PWA_WL 5 , PWA_WL 1 , and PWA_BL) output from the master unit  210 . The slave units  22   i  and  230  may generally have the same structure and operation, with the exception that the slave unit  22   i  may receive one “random” bit signal Ai (e.g., wherein I=0˜n) of a column address signal and may delay the signal Ai based on WL, thereby generating a delayed column address bit signal CAi, while the slave unit  230  may receive one random bit signal BA 0  of a bank address signal and may delay the signal BA 0  based on input latency, thereby generating a delay bank address signal BAL 0 . 
     In the example embodiment of  FIG. 4 , the slave unit  22   i  for the column address signal may include a plurality of flip-flops (e.g., three flip-flops  411 ,  412 , and  413 ) and a multiplexer  421 . The first flip-flop  411  may receive the second write master signal PWA_WL 5  through a clock terminal CK and the column address bit signal Ai through an input terminal. Accordingly, the first flip-flop  411  may output an input signal in response to the second write master signal PWA_WL 5 . The second flip-flop  412  may receive the first write master signal PWA_WL 1  through a clock terminal CK and an output signal of the multiplexer  421  through an input terminal. The multiplexer  421  may select and output one of the column bit address signal Ai and an output signal of a previous or preceding flip-flop (e.g., the first flip-flop  411 ) in response to a write latency code signal WL_ 1234 . The write latency code signal WL_ 1234  may be activated (e.g., set to the first logic level, such as a higher logic level or logic “1”) if the input latency is 1 through 4 and may be deactivated (e.g., set to the second logic level, such as a lower logic level or logic “0”) if the input latency is 5 or greater. Consequently, the second flip-flop  412  may receive the output signal of the multiplexer  421  as an input signal and may output the received input signal in response to the first write master signal PWA_WL 1 . The third flip-flop  413  may receive the burst master signal PWA_BL through a clock terminal CK and an output signal of the second flip-flop  412  through an input terminal. Accordingly, the third flip-flop  413  may output an input signal in response to the burst master signal PWA_BL. An output signal of the third flip-flop  413  may be the delayed column address bit signal CAi. 
     In the example embodiment of  FIG. 4 , the structure and operation of the slave unit  230  for the bank address signal may be the same as that of the slave unit  22   i  for the column address signal. Thus, a detailed description thereof will be omitted for the sake of brevity. 
     In the example embodiment of  FIG. 4 , the slave unit  22   i  and/or  230  may receive the column or bank address signal Ai or BA 0  and may sequentially latch the address signal Ai and/or BA 0  in response to the master signals PWA_WL 5 , PWA_WL 1 , and PWA_BL, which may be sequentially activated (e.g., set to the first logic level, such as a higher logic level or logic “1”) by the master unit  210 , thereby outputting the address signal Ai or BA 0  that has been delayed by (WL+BL/2). 
       FIG. 5A  is a signal timing chart illustrating an operation of the latency control circuit  200  of  FIG. 2  when the WL is 6 according to another example embodiment of the present invention.  FIG. 5B  is a signal timing chart illustrating an operation of the latency control circuit  200  of  FIG. 2  when the WL is 4 according to another example embodiment of the present invention.  FIGS. 5A and 5B  illustrate signals transitions during a progression of clock signals, which are shown as a series of time units from time  0  to time  10 . 
     In the example embodiments of  FIGS. 5A and 5B , if a write command WR is input from an external entity at time  0 , the write command signal PWA may be generated. In addition, the address signal ADD designating a memory cell to which input data D 0  through D 7  may be written may also be input along with the write command WR. After the write command WR is input at the time  0 , another command may be input at an interval of tCCD. However, the descriptions of  FIGS. 5A and 5B  are given below with respect to a single write command WR input at the time  0  for the sake of clarity. 
     Example operation of the latency control circuit  200  performed when the WL equals 6 and tCCD is 4 tCK will now be described with reference to  FIGS. 3 ,  4  and  5 A below. 
     In example operation of the latency control circuit  200  when the WL equals 6, with reference to  FIGS. 3 ,  4  and  5 A, in the write master signal generator  310  included in the master unit  210 , because WL is 6, the latency signal WL 6  may be activated (e.g., set to the first logic level) and the remaining latency signals WLi (where i=1, 2, 3, 4, 5, 7) may be deactivated (e.g., set to the second logic level). Accordingly, the sixth multiplexer  326  may select and output the write command signal PWA and the remaining multiplexers  325  through  321  may select and output the output signals of the previous or preceding flip-flops  316  through  312 , respectively. As a result, the write command signal PWA may be input to the sixth flip-flop  316  and then output in synchronization with the internal clock signal PCLK. The fifth multiplexer  325  may select and output the output signal of a preceding flip-flop (e.g., the sixth flip-flop  316 ), and therefore, the fifth flip-flop  315  may receive the output signal of the sixth flip-flop  316 . The fifth flip-flop  315  may output the input signal in response to the internal clock signal PCLK. The other multiplexers  324 ,  323 ,  322 , and  321  may select and output the output signals of their preceding flip-flops, respectively, and therefore, the flip-flops  324  through  321  may also receive the output signals of their previous flip-flops, respectively, and may output their input signals in response to the internal clock signal PCLK. The output signal of the fifth flip-flop  315  may be output as the second write master signal PWA_WL 5  and the output signal of the first flip-flop  311  may be output as the first write master signal PWA_WL 1 . Accordingly, the second write master signal PWA_WL 5  may be generated if the write command signal PWA is delayed by about 2 tCK and the first write master signal PWA_WL 1  may be generated if the write command signal PWA is delayed by a number of clock cycles corresponding to the WL (e.g., in this example, by about 6 tCK because WL equals 6). 
     In example operation of the latency control circuit  200  when the WL equals 6, with reference to  FIGS. 3 ,  4  and  5 A, the burst master signal generator  330  may delay the final output signal of the write master signal generator  310  (e.g., the first write master signal PWA_WL 1 ) by 4 tCK, thereby outputting the burst master signal PWA_BL. 
     In example operation of the latency control circuit  200  when the WL equals 6, with reference to  FIGS. 3 ,  4  and  5 A, in the slave units  22   i  and  230 , the address signal ADD (e.g., including the column and bank address signals A and BA) may be output in response to the second write master signal PWA_WL 5 . The, the address signal ADD, output in response to the second write master signal PWA_WL 5 , may be output in response to the first write master signal PWA_WL 1 . The address signal ADD, output in response to the first write master signal PWA_WL 1 , may be output in response to the burst master signal PWA_BL, thereby generating the delayed column and bank address signals CA and BAL. Accordingly, the delayed column and bank address signals CA and BAL may be generated after (WL+BL/2) tCK (e.g., 10 tCK or time  10 ) after the input time  0  of the address signal ADD. 
     Example operation of the latency control circuit  200  performed when the WL equals 4 and tCCD is 4 tCK will now be described with reference to  FIGS. 3 ,  4  and  5 B below. 
     In example operation of the latency control circuit  200  when the WL equals 4, with reference to  FIGS. 3 ,  4  and  5 B, in the write master signal generator  310  included in the master unit  210 , the latency signal WL 4  may be activated (e.g., set to the first logic level) and the remaining latency signals WLi (where i=1, 2, 3, 5, 6, 7) may be deactivated (e.g., set to the second logic level). Accordingly, the fourth multiplexer  324  may select and output the write command signal PWA. The write command signal PWA may sequentially pass through the third, second, and first flip-flops  323 ,  322 , and  321 . Thus, the write command signal PWA may be latched by the fourth flip-flop  324 , an output signal of the fourth flip-flop  324  may be latched by the third flip-flop  323 , an output signal of the third flip-flop  323  may be latched by the second flip-flop  322  and an output signal of the second flip-flop  322  may be latched by the first flip-flop  321 . Accordingly, an output signal of the fifth flip-flop  325  (e.g., the second write master signal PWA_WL 5 ) may not be activated (e.g., thereby remaining at the second logic level). In addition, the output signal of the first flip-flop  321  (e.g., the first write master signal PWA_WL 1 ) may be generated after a number of clock cycles corresponding to WL (e.g., 4 tCK or clock cycles) because the write command signal PWA may be input to the write master signal generator  310 . 
     In example operation of the latency control circuit  200  when the WL equals 4, with reference to  FIGS. 3 ,  4  and  5 B, the burst master signal generator  330  may delay the final output signal of the write master signal generator  310  (e.g., the first write master signal PWA_WL 1 ) by 4 tCK, thereby outputting the burst master signal PWA_BL. 
     In example operation of the latency control circuit  200  when the WL equals 4, with reference to  FIGS. 3 ,  4  and  5 B, in the slave units  22   i  and  230 , the address signal ADD, including the column and bank address signals A and BA, may be output in response to the first write master signal PWA_WL 1 . The address signal ADD, output in response to the first write master signal PWA_WL 1 , may be output in response to the burst master signal PWA_BL, thereby generating the delayed column and bank address signals CA and BAL. Accordingly, the delayed column and bank address signals CA and BAL may be generated after (WL+BL/2) tCK (e.g., 8 tCK or clock cycles) following the input time  0  of the address signal ADD. A plurality of delayed column and bank address signals CA and BAL may be generated at an interval of tCCD (e.g., 4 tCK). 
     In the above-described example operation of  FIGS. 5A and 5B , tCCD=4 and BL=8. However, it is understood that other example embodiments of the present invention may be directed to the master unit  210  and the slave units  22   i  and  230  configured for operation with any value of tCCD and/or BL. 
       FIGS. 6 and 7  are circuit diagrams illustrating a master unit  610  and a slave unit  710 , respectively, according to another example embodiment of the present invention. In the example embodiments of  FIGS. 6 and 7 , an example wherein tCCD=2 and BL=4 may be illustrated, while it is understood that other example embodiments of the present invention need not be limited to structures configured for operation with such values. 
     In the example embodiment of  FIG. 6 , the master unit  610  may have a structure and operation similar to the master unit  210  illustrated in  FIG. 3 . However, the master unit  610  may output additional write master signals PWA_WL 7  and PWA_WL 3  such that an interval between write master signals may be an integer multiple of tCCD (e.g., 2 tCK). In addition, because BL=4, a burst master signal PWA_BL′ may be output after BL/2 clock cycles (i.e., 2 tCK) following the output of the first write master signal. Accordingly, an output signal of the ninth flip-flop  332  may be output as the burst master signal PWA_BL′. Thus, the tenth and eleventh flip-flops  333  and  334  need not be included. 
     In the example embodiment of  FIG. 7 , the slave unit  710  may further include flip-flops  711  and  713  responding to the additional write master signals PWA_WL 7  and PWA_WL 3 , as compared to the slave units  22   i  and  230  illustrated in  FIG. 4 . The slave unit  710  may include flip-flops  711  through  715  responding to the five master signals PWA_WL 7 , PWA_WL 5 , PWA_WL 3 , PWA_WL 1 , and PWA_BL′, respectively, output from the master unit  610 . The slave unit  710  may further include multiplexers  721  through  723 . 
     In the example embodiment of  FIG. 7 , each of the multiplexers  721  through  723  may select and output one of an output signal of a previous or preceding flip-flop and the address signal (Ai+BA 0 ) in response to a corresponding WL code signal WL_ 56 , WL_ 34  and/or WL_ 12 . The WL code signals WL_ 56 , WL_ 34  and WL_ 12  may be activated (e.g., set to the first logic level) based on WL information. For example, if the WL is 1 or 2, the WL code signal WL_ 12  may be activated. Alternatively, if the WL is 3 or 4, the WL code signal WL_ 34  may be activated. In another alternative example, if the WL is 5 or 6, the WL code signal WL_ 56  may be activated. Accordingly, if the WL is 1 or 2, the address signal Ai or BA 0  may be sequentially delayed by the flip-flops  714  and  715  and then output as the delayed column or bank address signal CAi or BAL 0 . If the WL is 3 or 4, the address signal Ai or BA 0  may be sequentially delayed by the flip-flops  713 ,  714 , and  715  and then output as the delayed column or bank address signal CAi or BAL 0 , and so on. 
     In the example embodiment of  FIG. 7 , the slave unit  710  may receive the column or bank address signal Ai or BA 0  and may sequentially latch and output the received column/bank address signal Ai/BA 0  in response to a master signal activated among the master signals PWA_WL 7 , PWA_WL 5 , PWA_WL 3 , PWA_WL 1 , and PWA_BL′ may be sequentially output from the master unit  610 . As a result, the slave unit  710  may output the received address signals Ai and BA 0  after delaying them by (WL+BL/2) clock cycles. 
       FIG. 8  is a block diagram of a latency control circuit  200 ′ according to another example embodiment of the present invention. In the example embodiment of  FIG. 8 , similar to the latency control circuit  200  illustrated in  FIG. 2 , the latency control circuit  200 ′ may include a master unit  810  and a plurality of slave units  82   i  and  830  (e.g., wherein I=0˜n) and may control a generation time of the column address signal CA and the bank address signal BAL based on the WL signal WLi (e.g., wherein i may be a positive integer). 
       FIG. 9  is a circuit diagram of the master unit  810  of  FIG. 8  according to another example embodiment of the present invention. In the example embodiment of  FIG. 9 , the master unit  810  may include a plurality of registers  911  through  918  connected in series and a plurality of combiners  921  through  925 . In an example, each of the registers  911  through  918  may be implemented by a flip-flop and each of the combiners  921  through  925  may be implemented by an AND gate. Thus, for clarity of the description, the flip-flops (e.g., registers  911  through  918 ) may be referred to as first through eighth flip-flops  911  through  918  and the AND gates may be referred to as first through fifth AND gates  921  through  925 . 
     In the example embodiment of  FIG. 9 , the first through eighth flip-flops  911  through  918  may be connected in series and may receive the internal clock signal PCLK through their clock terminals CK. The first flip-flop  911  may receive the write command signal PWA as an input signal and the second through eighth flip-flops  912  through  918  may receive output signals, respectively, of previous or preceding flip-flops (e.g., among the flip-flops  911  through  918 ), as input signals. The first through eighth flip-flops  911  through  918  may output their respective input signals in synchronization with the internal clock signal PCLK. Accordingly, the first through eighth flip-flops  911  through  918  may generate write command signals delayed by 1 through 8 tCK, respectively. 
     In the example embodiment of  FIG. 9 , the first AND gate  921  may perform an AND operation on the write command signal PWA and the internal clock signal PCLK, thereby generating a first master signal CLK 0 . The second AND gate  922  may perform an AND operation on an output signal of the second flip-flop  912  (e.g., a 2 tCK delayed write command signal) and the internal clock signal PCLK, thereby generating a second master signal CLK 2 . The third AND gate  923  may perform an AND operation on an output signal of the fourth flip-flop  914  (e.g., a 4 tCK delayed write command signal) and the internal clock signal PCLK, thereby generating a third master signal CL. The fourth AND gate  924  may perform an AND operation on an output signal of the sixth flip-flop  916  (e.g., a 6 tCK delayed write command signal) and the internal clock signal PCLK, thereby generating a fourth master signal CLK 6 . The fifth AND gate  925  may perform an AND operation on an output signal of the eighth flip-flop  918  (e.g., an 8 tCK delayed write command signal) and the internal clock signal PCLK, thereby generating a fifth master signal CLK 8 . 
     In the example embodiment of  FIG. 9 , the master unit  810  may delay the write command signal PWA by integer multiples of the internal clock signal PCLK (e.g., integer multiples of a clock cycle) and may output a given signal among the delayed signals as a master signal. “Master signals” may be output at an interval of an integer multiple of tCCD. In an example, the tCCD may be 2, and therefore, the first through fifth master signals CLK 0 , CLK 2 , CLK 4 , CLK 6  and CLK 8  may have an interval of 2 tCK. 
       FIG. 10  is a circuit diagram of a slave unit  82   i  (e.g., wherein I=0˜n) of  FIG. 8  according to another example embodiment of the present invention. In the example embodiment of  FIG. 10 , the slave unit  82   i  may operate in response to the output signals CLK 0 , CLK 2 , CLK 4 , CLK 6  and CLK 8  of the master unit  810  illustrated in  FIG. 9 . 
     In the example embodiment of  FIG. 10 , the slave unit  82   i  may include a plurality of registers  1011  through  1015  connected in series, a plurality of switches  1021  through  1025  and an output latch  1030 . In an example, each of the registers  1011  through  1015  may be implemented by a flip-flop and each of the switches  1021  through  1025  may be implemented as a transmission gate. 
     In the example embodiment of  FIG. 10 , the slave unit  82   i  may generate a delayed address bit signal CAi (e.g., wherein I=0˜n) corresponding to a random bit Ai of an address signal in response to the master signals CLK 0 , CLK 2 , CLK 4 , CLK 6  and CLK 8  output from the master unit  810 . Thus, the first through fifth flip-flops  1011  through  1015  may receive the first through fifth master signals CLK 0 , CLK 2 , CLK 4 , CLK 6  and CLK 8 , respectively, through their respective clock terminals CK. The first flip-flop  1011  may receive the address signal Ai and may output the received address signal Ai in response to the first master signal CLK 0 . The second through fifth flip-flops  1012  through  1015  may receive output signals of previous flip-flops  1011  through  1014 , respectively, and may output the respectively received signals in response to the second through fifth master signals CLK 2 , CLK 4 , CLK 6 , and CLK 8 , respectively. 
     In the example embodiment of  FIG. 10 , because the first through fifth master signals CLK 0 , CLK 2 , CLK 4 , CLK 6  and CLK 8  may have an interval of 2 tCK, the first through fifth flip-flops  1011  through  1015  may generate address signals Ai_ 12 , Ai_ 34 , Ai_ 56 , Ai_ 78  and Ai_ 910  by delaying the address signal Ai by 0, 2, 4, 6 and 8 tCK, respectively. 
     In the example embodiment of  FIG. 10 , the output signals Ai_ 12 , Ai_ 34 , Ai_ 56 , Ai_ 78 , and Ai_ 910  of the first through fifth flip-flops  1011  through  1015  may be selectively transmitted to the output latch  1030  through the first through fifth switches  1021  through  1025 , which may be closed or opened in response to WL code signals WL_ 12 , WL_ 34 , WL_ 56 , WL_ 78  and WL_ 910 . 
     In the example embodiment of  FIG. 10 , the WL code signals WL_ 12 , WL_ 34 , WL_ 56 , WL_ 78  and WL_ 910  may be activated (e.g., set to the first logic level) based on a WL signal. For example, if the WL is 1 or 2, the WL code signal WL_ 12  may be activated. Alternatively, if the WL is 3 or 4, the WL code signal WL_ 34  may be activated. In another alternative example, if WL is 5 or 6, the WL code signal WL_ 56  may be activated. In an example, assume WL is 9, and therefore, the WL code signal WL_ 910  may be activated. Accordingly, the output signal Ai_ 910  of the fifth flip-flop  1015  may be transmitted to the output latch  1030 . A temporary latch (not shown) may be provided before the output latch  1030  to temporarily latch signals output from the first through fifth switches  1021  through  1025 . The output latch  1030  may outputs a received input signal as a delayed address signal CAi in response to a latch clock signal LCLK. The latch clock signal LCLK may be obtained by combining a signal resulting from delaying the write command WR by WL or (WL+AL) clock signals with the internal clock signal PCLK. Accordingly, the latch clock signal LCLK may be generated after WL or (WL+AL) clock signals following the input of the write command WR. 
     In the example embodiment of  FIG. 10 , the slave unit  82   i  may receive the column address signal Ai and may outputs the received column address signal Ai in response to the master signals CLK 0 , CLK 2 , CLK 4 , CLK 6  and CLK 8  sequentially generated by the master unit  810 . Thus, the slave unit  82   i  may delay the received column address signal Ai by WL clock cycles and may then output the delayed column address signal Ai. It will be readily apparent that the slave unit  82   i  illustrated in  FIG. 10  may alternatively be used to process a bank address signal. Further, a number of flip-flops and/or switches included in the slave unit  82   i  may vary in other example embodiments of the present invention, for example, based on a maximum value of the WL and/or a value of the tCCD. 
     In the example embodiment of  FIG. 10 , the master unit  810  and the slave unit  82   i  illustrated in  FIGS. 9 and 10  may correspond to example conditions where the tCCD may equal 2. In an alternative example, if the tCCD is 4, master signals output from the master unit  810  may be output at an interval of 4 tCK. Accordingly, only the first, third, and fifth master signals CLK 0 , CLK 4 , and CLK 8  need be output from the master unit  810  illustrated in  FIG. 9  and the second and fourth master signals CLK 2  and CLK 6  need not be output. Thus, the second and fourth flip-flops  1012  and  1014  receiving the second and fourth master signals CLK 2  and CLK 6  in the slave unit  82   i  need not be included, and therefore, the number of flip-flops included in a slave unit may be reduced. 
       FIG. 11  is a signal timing chart illustrating an operation of the latency control circuit  200 ′ of  FIG. 8  when the WL is 9 according to another example embodiment of the present invention. Example operation of the latency control circuit  200 ′ will be described below in greater detail with reference to  FIGS. 9 ,  10 , and  11  below. 
     In example operation of the latency control circuit  200 ′ of  FIG. 8  and when WL equals 9, with reference to  FIGS. 9 ,  10  and  11 , the write command WR may be input from an external entity at time  0 , and the write command signal PWA may thereafter generated (e.g., during time  1 ). In addition, the address signal ADD may be input along with the write command WR. 
     In example operation of the latency control circuit  200 ′ of  FIG. 8  and when WL equals 9, with reference to  FIGS. 9 ,  10  and  11 , the write command signal PWA may be combined (e.g., via an AND operation) with the internal clock signal PCLK, thereby generating the first master signal CLK 0 . In addition, 2, 4, 6, and 8 tCK delayed write command signals may be combined (e.g., via AND operations) with the internal clock signal PCLK, thereby generating the second, third, fourth, and fifth master signals CLK 2 , CLK 4 , CLK 6 , and CLK 8 . 
     In example operation of the latency control circuit  200 ′ of  FIG. 8  and when WL equals 9, with reference to  FIGS. 9 ,  10  and  11 , the slave unit  82   i  may sequentially output the received address signal Ai in response to the master signals CLK 0 , CLK 2 , CLK 4 , CLK 6  and CLK 8  generated by the master unit  810 , thereby generating 0, 2, 4, 6, and 8 tCK delayed address signals Ai_ 12 , Ai_ 34 , Ai_ 56 , Ai_ 78  and Ai_ 910 , respectively. Accordingly, as shown in  FIG. 11 , the address signals Ai_ 56 , Ai_ 78 , and Ai_ 910  may be representative of the received address signal Ai delayed by 4, 6, and 8 tCK, respectively. 
     In example operation of the latency control circuit  200 ′ of  FIG. 8  and when WL equals 9, with reference to  FIGS. 9 ,  10  and  11 , a given address signal (e.g., Ai_ 910 ) among the delayed address signals Ai_ 12 , Ai_ 34 , Ai_ 56 , Ai_ 78  and Ai_ 910  may be latched in response to the latch clock signal LCLK, thereby generating the delayed address signal CAi. Delayed address signals CAi may be generated at an interval of tCCD (e.g., 2 tCK), however, for simplicity of explanation, the delayed address signal CAi corresponding to a single write command WR input at the time  0  is illustrated in  FIG. 11 . 
     The latency control circuits  200  and  200 ′ according to the example embodiments of  FIGS. 2 and 8 , respectively, may be configured to delay an address signal (e.g., control a generation time of the address signal) based on latency information, such as WL information. However, it is understood that latency control circuits according to other example embodiments of the present invention are not restricted thereto and may alternatively be used to delay a command signal (e.g., the generation time of the command signal) based on latency information. 
       FIG. 12  is a block diagram of the command detection circuit  180  of  FIG. 1  according to another example embodiment of the present invention. In the example embodiment of  FIG. 12 , the command detection circuit  180  may include a command buffer  1210  and a command decoder  1220 . If the semiconductor memory device  100  includes the command detection circuit  180  as illustrated in  FIG. 12 , a latency control process need not be used with respect to a command signal. 
       FIG. 13  is a block diagram of a command detection circuit  180 ′ according to another example embodiment of the present invention. In the example embodiment of  FIG. 13 , the command detection circuit  180 ′ may include the command buffer  1210 , a latency control circuit  1300  and the command decoder  1220 . If the semiconductor memory device  100  includes the command detection circuit  180 ′ illustrated in  FIG. 13 , the latency control process (e.g., above described with respect to  FIGS. 1 through 11 ) may be used with respect to a command signal. 
     In the example embodiment of  FIG. 13 , the latency control circuit  1300  may control the internal generation time of the command signal CMD (e.g., /WE, /CS, /CAS, etc.) based on the AL signal ALj (e.g., wherein “j” may be a positive integer). Thus, the latency control circuit  1300  may delay the command signal CMD based on the AL signal ALj. 
       FIG. 14  is a block diagram of the latency control circuit  1300  according to another example embodiment of the present invention. In the example embodiment of  FIG. 14 , the latency control circuit  1300 , similar the latency control circuits  200  and  200 ′ illustrated in  FIGS. 2 and 8 , respectively, may include a master unit  1310  and a plurality of slave units  132   i  (e.g., wherein I=0˜k). 
     In the example embodiment of  FIG. 14 , the master unit  1310  may generate one or more master signals MCLK in response to the internal clock signal PCLK, a command reference signal INCMD and the AL signal ALj. The command reference signal INCMD may be referred to when the master signals MCLK having an interval of an integer multiple of the internal clock signal PCLK (e.g., an integer multiple of a clock cycle) is generated. For example, the command reference signal INCMD may be a /CS signal activated (e.g., set to the first logic level) if a command signal is applied from an external entity to the semiconductor memory device  100  or may alternatively be a signal based on the /CS signal. 
     In the example embodiment of  FIG. 14 , the slave units  132   i  may latch and output corresponding command signals (e.g., /WE, /CS, and /CAS, respectively) in response to the master signals MCLK generated by the master unit  210 . As a result, the slave units  132   i  may delay their respective received command signals /WE, /CS, and /CAS by AL clock cycles. 
     In the example embodiment of  FIG. 14 , the master unit  1310  may have a similar structure as the master unit  210 ,  610  and/or  810 , and the slave unit  132   i  (e.g., wherein I=0˜k) may have a similar structure as the slave unit  22   i ,  710  or  82   i , except with respect to input and output signals included therein. Thus, detailed descriptions of the structures and operations of the master unit  1310  and the slave unit  132   i  have been omitted for the sake of brevity. 
     In the example embodiment of  FIG. 14 , the latency control circuit  1300  may be disposed before the command decoder  1220 . However, in another example embodiment of the present invention, while not shown, the latency control circuit  1300  may be disposed after the command decoder  1220 . Thus, a decoded command signal may be controlled according to the AL. 
     In the example embodiment of  FIG. 14 , the write command signal PWA may be generated based on AL information. For example, the write command signal PWA may be generated or activated (e.g., set to the first logic level) after a number of clock cycles corresponding to the AL following an input of the write command signal PWA from an external entity. Accordingly, the column or bank address signal CA or BAL may be controlled based on the write command signal PWA, delayed corresponding to the AL, and may be generated based on the AL and WL information. Alternatively, the write command signal PWA may be “immediately” (e.g., without delays) generated irrespective of the latency information and the column or bank address signal CA or BAL may be generated based on the AL and WL information. 
     In the example embodiment of  FIG. 14 , a plurality of master signals, which may be generated from a master unit of a latency circuit, may be set to have an interval of about tCCD. However, it is understood that other example embodiments of the present invention may be directed to master signals having different intervals. 
       FIG. 15  is a block diagram of a latency control circuit  200 ″ according to another example embodiment of the present invention. 
     In the example embodiment of  FIG. 15 , similar to the latency control circuits  200  and  200 ′ described above, the latency control circuit  200 ″ illustrated in  FIG. 15  may further include a master unit  410  and a slave unit  420 . While only one slave unit  420  is illustrated in  FIG. 15 , it is understood that any number of slave units (e.g., corresponding to the number of bits in an address signal) may be included within the latency control circuit  200 ″ in other example embodiments of the present invention. For example, the latency control circuit  200 ″ may include a plurality of slave units, each of which may receive a plurality of master signals CSi output from the master unit  410 . As will be described hereinafter, for example purposes, it may be assumed that the latency control circuit  200 ″ is embodied so as to satisfy the conditions of tCCD=2, BL=4 and a maximum value of WL is 7. 
     In the example embodiment of  FIG. 15 , the master unit  410  may include a plurality of registers  411  through  419  and a plurality of the multiplexers  321  through  327 , which may be connected in cascade or series. In an example, each of the registers  411  through  419  may be implemented by a flip-flop. The number of flip-flops included in the master unit  410  may be determined by the maximum value of the WL and the BL. For example, if the maximum value of the WL is M (e.g., where M may be a natural number, or a positive integer greater than or equal to 1) and the burst length is BL, the master unit  410  may include at least (M+BL/2) flip-flops. 
     In the example embodiment of  FIG. 15 , a structure of the master unit  410  may be similar to that of the master unit  210  illustrated in  FIG. 3 . In the master unit  410 , blocks  410 - 1  and  410 - 2  may correspond to the write master signal generator  310  and the burst master signal generator  330 , respectively, included in the master unit  210  illustrated in  FIG. 3 . However, the master unit  410  may differ from the master unit  210  in that an interval among the plurality of master signals CSi (e.g., CS 1  through CS 6 ) output from the master unit  410  may not be an integer multiple of tCCD. For example, an interval between adjacent master signals among the plurality of master signals CSi output from the master unit  410  may be selected within a range that does not exceed the tCCD. 
     In the example embodiment of  FIG. 15 , in an example, an interval between master signals may not be greater than (BL/2-0.5) tCK, or tCCD-0.5 tCK. 0.5 tCK may be a margin considered if a signal (e.g., PWA or Ai) is transmitted through a flip-flop. However, such a margin may be adjusted as necessary. Accordingly, an interval between adjacent master signals may not be greater than (BL/2-α) tCK, where α may refer a real number which is at least equal to 0 and less than tCCD. In order to adjust an interval between master signals to (BL/2-α) tCK instead of tCCD, output signals from an internal node of a flip-flop may be included in a master unit. The structure of such a flip-flop will be described in greater detail later. 
     In the example embodiment of  FIG. 15 , an interval between the master signals CSi may be (BL/2-0.5) tCK (e.g., 1.5 tCK). However, the interval between the master signals CSi need not be limited to a relatively constant 1.5 tCK. Rather, the interval may be set to any well known value, such as 1.5 tCK and 1.0 tCK. In addition, in order to adjust the entire delay time, at least one value of the interval between the master signals CSi may be 1.0 tCK or less (e.g., 0.5 tCK). 
     In the example embodiment of  FIG. 15 , the slave unit  420  may include a plurality of flip-flops  421  through  426  (e.g., 6) and multiplexers  431  through  435 . The flip-flops  421  through  426  in the slave unit  420  may be connected in series and may each receive an input signal in response to a corresponding signal among the plurality of the master signals CSi output from the master unit  410 . The slave unit  420  may further include a flip-flop  427  which may latch and output an address signal TAi in response to the write command signal PWA. The address signal TAi may be the signal ADD output from the address buffer  120  illustrated in  FIG. 1 . The flip-flop  427  may latch a previous address signal before the address buffer  120  may output a subsequent address signal. 
     In the example embodiment of  FIG. 15 , each of the multiplexers  431  through  435  may select and output one of an output signal of a previous or preceding flip-flop and the address signal Ai in response to a corresponding signal among WL code signals WL_ 1 , WL_ 2 , WL_ 34 , WL_ 5  and WL_ 67 . The WL code signals WL_ 1 , WL_ 2 , WL_ 34 , WL_ 5 , and WL_ 67  may be activated (e.g., set to the first logic level) based on the WL information. For example, the WL code signal WL_ 1  may be activated (e.g., set to the first logic level) if WL=1, the WL code signal WL_ 2  may be activated if WL=2, the WL code signal WL_ 34  may be activated if WL=3 or 4, the WL code signal WL_ 5  may be activated if WL=5, and the WL code signal WL_ 67  may be activated if WL=6 or 7. Accordingly, if WL=1, the address signal Ai may be sequentially delayed by the flip-flops  422  and  421  and a delayed address signal CAi may be generated. If WL=6 or 7, the address signal Ai may be sequentially delayed by the flip-flops  426 ,  425 ,  424 ,  423 ,  422  and  421  and a delayed address signal CAi may be generated. 
     In the example embodiment of  FIG. 15 , the slave unit  420  may receive the address signal Ai and may sequentially latch the address signal Ai in response to activated signals (e.g., set to the first logic level) among the plurality of the master signals CSi generated by the master unit  410 . Thus, the address signal Ai may be delayed by (WL+BL/2) clock cycles. 
       FIG. 16A  is a signal timing chart illustrating an operation of the latency control circuit  200 ″ of  FIG. 15  when the WL is 7 and the BL is 4, according to another example embodiment of the present invention. Example operation of the latency control circuit  200 ″ when the WL is 7 and BL is 4 will now be described in greater detail with reference to  FIGS. 15 and 16A . 
     In example operation of the latency control circuit  200 ″ of  FIG. 15  when the WL is 7 and the BL is 4, with reference to  FIGS. 15 and 16A , the latency signal WL 7  may be activated (e.g., set to the first logic level) and the remaining latency signals WLi (e.g., wherein I=1 through 6) may be deactivated (e.g., set to the second logic level). Accordingly, the multiplexer  327  may select and output the write command signal PWA and remaining multiplexers  326  through  321  may select and output corresponding previous or preceding flip-flops  419  through  414 . The write command signal PWA may be input to the flip-flop  419  and may be output in synchronization with a rising edge of the internal clock signal PCLK. An output signal of the flip-flop  419  may be input to the subsequent flip-flop  418  and may be output as a first master signal CS 1  in synchronization with a falling edge of the internal clock signal PCLK, and may also be output in synchronization with a rising edge of the internal clock signal PCLK. An output signal of the flip-flop  418  may be input to the subsequent flip-flop  417  and may be output in synchronization with a rising edge of the internal clock signal PCLK. In this way, the write command signal PWA may be passed through the nine flip-flops  419  through  411  and first through sixth master signals CS 1  through CS 6  may be generated at a given interval (e.g., about 1.5 tCK). Thus, the first through sixth master signals CS 1  through CS 6  may be sequentially activated about with delays of 1.5, 3, 4.5, 6, 7.5, and 8 tCK, respectively, following the time  0  (e.g., when the write command WR and the address signal ADD are received). 
     In example operation of the latency control circuit  200 ″ of  FIG. 15  when the WL is 7 and the BL is 4, with reference to  FIGS. 15 and 16A , the slave unit  420  may output the address signal Ai in response to the first master signal CS 1  and may output a given signal (e.g., the receipt of which may be triggered by the first master signal CS 1 ) in response to the second master signal CS 2 . Thus, the slave unit  420  may sequentially delay the address signal Ai in response to the first through sixth master signals CS 1  through CS 6  and the delayed address signal CAi. Thus, the delayed address signal CAi may be generated (WL+BL/2) tCK (e.g., 9 tCK) following the time  0  when the write command WR and the address signal ADD are input. 
       FIG. 16B  is a signal timing chart illustrating an operation of the latency control circuit  200 ″ of  FIG. 15  when the WL is 1 and the BL is 4 according to another example embodiment of the present invention. Example operation of the latency control circuit  200 ″ when the WL is 1 and BL is 4 will now be described in greater detail with reference to  FIGS. 15 and 16B . 
     In example operation of the latency control circuit  200 ″ of  FIG. 15  when the WL is 1 and the BL is 4, with reference to  FIGS. 15 and 16B , the latency signal WL 1  may be activated (e.g., set to the first logic level) and the remaining latency signals WLi (e.g., wherein i=2 through 7) may be deactivated (e.g., set to the second logic level). Accordingly, the write command signal PWA may be input to the flip-flop  413  and may be output in synchronization with a rising edge of the internal clock signal PCLK. An output signal of the flip-flop  413  may be input to the subsequent flip-flop  412  and may be output as the fifth master signal CS 5  in synchronization with a falling edge of the internal clock signal PCLK, and may further be output in synchronization with a rising edge of the internal clock signal PCLK. An output signal of the flip-flop  412  may be input to the subsequent flip-flop  411  and may be output in synchronization with a rising edge of the internal clock signal PCLK. An output signal of the flip-flop  411  may be the sixth master signal CS 6 . Accordingly, the write command signal PWA may be passed through the three flip-flops  413  through  411  and the fifth and sixth master signals CS 5  and CS 6  may be generated at a given interval (e.g., about 1.5 tCK). Thus, the fifth and sixth master signals CS 5  and CS 6  may be sequentially activated about 1.5 and 3 tCK, respectively, after the time  0  when the write command WR and the address signal ADD are input. The remaining master signals CS 1  through CS 4  may thereby not be activated. 
     In example operation of the latency control circuit  200 ″ of  FIG. 15  when the WL is 7 and the BL is 4, with reference to  FIGS. 15 and 16B , the slave unit  420  may output the address signal Ai in response to the fifth master signal CS 5  and may output a given signal (e.g., the receipt of which may be triggered by the fifth master signal CS 5 ) in response to the sixth master signal CS 6 , thereby generating the delayed address signal CAi. Thus, the delayed address signal CAi may be generated (WL+BL/2) tCK (e.g., 3 tCK) after the time  0  when the write command WR and the address signal ADD are input. 
       FIGS. 17A and 17B  are circuit diagrams of flip-flops  1710  and  1720 , respectively, according to another example embodiment of the present invention. In an example, the flip-flops may be included within one or more of the latency control circuits  200 ,  200 ″, etc. 
     In the example embodiment of  FIG. 17A , the flip-flop  1710  may include switch elements TG 1  and TG 2  and inverters IV 1 , IV 2  and IV 3 . In an example, the switch elements TG 1  and TG 2  may each be implemented by a transmission gate. 
     In the example embodiment of  FIG. 17A , the first switch element TG 1  may receive an input signal in response to a clock signal PCLK set to the second logic level (e.g., a lower logic level or logic “0”) and may be turned off in response to the clock signal PCLK set to the first logic level (e.g., a higher logic level or logic “1”). The inverters IV 1 , IV 2  and IV 3  may function as latches. The input signal received through the first switch element TG 1  may be latched and may be output as a first output signal OUTf. The second switch element TG 2  may output the latched signal as a second output signal OUTr in response to the first logic level of the clock signal PCLK. Accordingly, the first output signal OUTf may be output at a first edge (e.g., a falling edge) of the clock signal PCLK and the second output signal OUTr may be output at a second edge (e.g., a rising edge) of the clock signal PCLK. Thus, an interval between the first output signal OUTf and the second output signal OUTr may be ½ of the clock cycle of the clock signal PCLK. 
     In the example embodiment of  FIG. 17B , the flip-flop  1720  may include a delay element  1721 , in addition to structure above described with respect to the flip-flop  1710  illustrated in  FIG. 17A . The delay element  1721  may delay a signal of an internal node (e.g., an output signal of the inverter IV 2 ) by a given delay time. Accordingly, an output signal OUTs of the delay element  1721  and the second output signal OUTr may have a given interval therebetween. The interval between the output signal OUTs of the delay element  1721  and the second output signal OUTr may be adjusted by adjusting the delay time of the delay element  1721 . Thus, an interval between master signals may be adjusted. 
       FIG. 18  is a block diagram of a semiconductor memory device  2200  according to another example embodiment of the present invention. In the example embodiment of  FIG. 18 , the semiconductor memory device  2200  may include a command detection circuit  2210 , an address buffer  2220 , a plurality of banks  2230 , a clock circuit  2240 , a latency control circuit  2250  and an auto-precharge control circuit  2300 . In an example, the semiconductor memory device  2200  may be representative of a DDR3 DRAM device having an operating frequency of 1.6 Gigahertz, 8 banks, and a column command delay (CCD) of 4. 
     In the example embodiment of  FIG. 18 , the command detection circuit  2210  may receive command signals /CS, /RAS, /CAS, and /WE and a given address bit signal A 10  from an external entity, may decode the received command signals, and may output an internal command signal (e.g., based on the decoding). For example, if the given address bit signal A 10  is set to the first logic level (e.g., a higher logic level or logic “1”) along with a write command, the command detection circuit  2210  may output a write auto-precharge command signal WAP. 
     In the example embodiment of  FIG. 18 , the address buffer  2220  may buffer externally input addresses A 0  through An and BA 0  through BA 2  and may output a buffered bank address bBA (e.g., addresses bBA 0  through bBA 2 ) and a memory cell address ADDRESS, which may indicate a bank and a memory cell, respectively, at which a write auto-precharge command will be executed. 
     In the example embodiment of  FIG. 18 , the plurality of the banks  2230  may each include a memory cell array and may function as data storage, in which data may be input to or output from, based on the buffered bank address bBA and the memory cell address ADDRESS, which may be output from the address buffer  2220 . A write auto-precharge operation may be performed with respect to the plurality of the banks  2230  according to the buffered bank address bBA and the write auto-precharge command signal WAP. The clock circuit  2240  may generate an internal clock signal PCLK based on an external clock signal ECLK. 
     In the example embodiment of  FIG. 18 , the latency control circuit  2250  may delay the write auto-precharge command signal WAP, the buffered bank address bBA, and the memory cell address ADDRESS by a given delay time in response to the internal clock signal PCLK and a latency control signal WLi and may output a delayed bank address signal dBA (e.g., signals dBA 0  through dBA 2 ) and a delayed memory cell address signal dADDRESS. The given delay time may correspond to a given write latency tWL plus a data burst period tBURST. In an example, the write latency tWL may be one clock cycle of the internal clock signal PCLK and the data burst period tBURST may be four clock cycles of the internal clock signal PCLK. 
     In the example embodiment of  FIG. 18 , the band address signal dBA and the memory cell address signal dADDRESS may be input to the plurality of the banks  2230  and the band address signal dBA may be input to the auto-precharge control circuit  2300 . Accordingly, after five clock cycles corresponding to the write latency tWL plus the data burst period tBURST following receipt of the write auto-precharge command signal WAP at to the latency control circuit  2250 , a write operation may be performed at a cell in a particular bank, designated by the band address signal dBA and the memory cell address signal dADDRESS, among the plurality of the banks  2230 . In an example, the latency control circuit  2250  may correspond to any one of the latency control circuits  200 ,  200 ′,  200 ″ and  1300 . 
     In the example embodiment of  FIG. 18 , the auto-precharge control circuit  2300  may delay a delayed write auto-precharge command signal dWAP and the band address signal dBA, which may be output from the latency control circuit  2250 , by a write recovery time tWR and may output a precharge main signal PAPB (e.g., signals PAPB 0  through PAPB 7 ) to the plurality of the banks  2230  in order to control a time at which a precharge operation starts after the write operation is finished. 
       FIG. 19  is a block diagram of the auto-precharge control circuit  2300  according to another example embodiment of the present invention. In the example embodiment of  FIG. 19 , the auto-precharge control circuit  2300  may include a precharge command delay unit  2310 , a bank address delay unit  2320  and a precharge main signal generator  2330 . 
     In the example embodiment of  FIG. 19 , the precharge command delay unit  2310  may output a plurality of first precharge command delay signals dWAP_d 3 , dWAP_d 7  and dWAP_d 11 , which may be enabled after different delay times subsequent to the input of the delayed write auto-precharge command signal dWAP, in response to the internal clock signal PCLK. Also, the precharge command delay unit  2310  may delay the delayed write auto-precharge command signal dWAP by as a given number of clock cycles (e.g., 12 clock cycles) of the internal clock signal PCLK corresponding to the write recovery time tWR, and may output a second precharge command delay signal ddWAP. 
     In the example embodiment of  FIG. 19 , an enabling interval among the first precharge command delay signals dWAP_d 3 , dWAP_d 7 , and dWAP_d 11  (e.g., an interval between a time when one of the first precharge command delay signals dWAP_d 3 , dWAP_d 7 , and dWAP_d 11  is enabled and a time when a subsequent first precharge command delay signal is enabled) may be less than or equal to a number of clock cycles of the internal clock signal PCLK (CCD=4), which may correspond to a minimum interval between commands, tCCD (e.g., because the bank address signals dBA 0 , dBA 1 , and dBA 2  may be changed at the minimum interval between commands, tCCD, such as 4 clock cycles). 
       FIG. 20  is a circuit diagram of the precharge command delay unit  2310  of  FIG. 19 , according to another example embodiment of the present invention. In the example embodiment of  FIG. 20 , the precharge command delay unit  2310  may include a first register array  2311  including a plurality of registers (e.g., corresponding to a number of clock cycles of the internal clock signal PCLK of the write recovery time tWR) connected in series. In an example, the write recovery time tWR may be 15 ns and a single clock cycle of the internal clock signal PCLK may be 1.25 ns, and therefore, the first register array  2311  may include 12 (e.g., 15/1.25) registers. 
     In the example embodiment of  FIG. 19 , the first precharge command delay signals dWAP_d 3 , dWAP_d 7 , and dWAP_d 11  may be output from the third, seventh and eleventh registers, respectively, among the 12 registers forming the first register array  2311 . The second precharge command delay signal ddWAP may be output from the “last” (e.g., twelfth register) among the 12 registers forming the first register array  2311 . 
     In the example embodiment of  FIG. 19 , the first precharge command delay signals dWAP_d 3 , dWAP_d 7 , and dWAP_d 11  and the second precharge command delay signal ddWAP may be respectively enabled at intervals of 3, 4, 4, and 1 clock cycles of the internal clock signal PCLK. Thus, the enabling intervals may be less than or equal to the number of clock cycles (CCD=4) of the internal clock signal PCLK corresponding to the minimum interval between commands, tCCD. 
     In the example embodiment of  FIG. 19 , the bank address delay unit  2320  may delay the bank address signals dBA 0 , dBA 1  and dBA 2  in response to the delayed write auto-precharge command signal dWAP and the first precharge command delay signals dWAP_d 3 , dWAP_d 7 , and dWAP_d 11 . 
       FIG. 21  is a circuit diagram of the bank address delay unit  2320  of  FIG. 19  according to another example embodiment of the present invention. In the example embodiment of  FIG. 21 , the bank address delay unit  2320  may include a plurality of second register arrays  2321 ,  2322  and  2323  in which registers numbering one more than a number of the first precharge command delay signals dWAP_d 3 , dWAP_d 7 , and dWAP_d 11  may be connected in series. 
     In the example embodiment of  FIG. 21 , the second register arrays  2321 ,  2322  and  2323 , first registers may latch and output bit signals dBA 0 , dBA 1  and dBA 2 , respectively, in response to the delayed write auto-precharge command signal dWAP and may output a signal dBA_d 1 . The remaining registers (e.g., other than the first register) in each of the second register arrays  2321 ,  2322  and  2323  may latch and output signals, which are output from their previous or preceding registers, in response to the first precharge command delay signals dWAP_d 3 , dWAP_d 7  and dWAP_d 11 , respectively. 
     In the example embodiment of  FIG. 21 , a bank delay signal ddBA (e.g., bank delay signals ddBA 0  through ddBA 2 ) may be enabled (e.g., set to the first logic level) in response to the first precharge command delay signals dWAP_d 3 , dWAP_d 7  and dWAP_d 11 , which may be enabled at intervals that may be less than or equal to a number of clock cycles (CCD=4) of the internal clock signal PCLK corresponding to the minimum interval between commands, tCCD, because a minimum interval between commands, tCCD, in DDR3 may correspond to four clock cycles of the internal clock signal PCLK. 
     In the example embodiment of  FIG. 21 , the precharge main signal generator  2330  may output the precharge main signal PAPB based on the bank delay signals ddBA 0  through ddBA 2  (e.g., the signal ddBA) and the second precharge command delay signal ddWAP. 
       FIG. 22  is a circuit diagram of the precharge main signal generator  2330  of  FIG. 19  according to another example embodiment of the present invention. In the example embodiments of  FIGS. 19 and 22 , the precharge main signal generator  2330  may include a decoder  2331  and an AND element array  2332 . 
     In the example embodiment of  FIG. 22 , the decoder  2331  may output a precharge sub-signal BANK (e.g., BANK 0  through BANK 7 ) corresponding to the plurality of the banks  2230 , respectively, based on the bank delay signal ddBA. 
     In the example embodiment of  FIG. 22 , the AND element array  2332  may include AND elements connected in parallel. Each of the AND elements may perform an AND operation on a corresponding one of the precharge sub-signals BANK 0  through BANK 7  and the second precharge command delay signal ddWAP. The second precharge command delay signal ddWAP may be a given signal output from the last register of the first register array  2311  by delaying the delayed write auto-precharge command signal dWAP by a given number of clock cycles (e.g., 12 clock cycles) of the internal clock signal PCLK. Accordingly, the precharge main signal PAPB output from the precharge main signal generator  2330  may be output after the write recovery time tWR subsequent to receiving the delayed write auto-precharge command signal dWAP. 
       FIG. 23  is a signal timing chart illustrating an operation of the auto-precharge control circuit  2300  according to another example embodiment of the present invention. Example operation of the auto-precharge control circuit  2300  will now be described with reference to  FIGS. 18 through 23 . 
     In example operation of the auth-precharge control circuit  2300 , with reference to  FIGS. 18 through 23 , the write command WR may be externally input at the minimum interval between commands, tCCD (e.g., 4 cycle clocks), in synchronization with a given rising edge of the external clock signal ECLK. The write command WR may be an external command determined by the combination of the command signals /CS, /RAS, /CAS, and /WE input to the command detection circuit  2210 . If the given bit signal A 10  is input at the first logic level (e.g., a higher logic level or logic “1”) along with the write command WR, the write auto-precharge command signal WAP may be internally generated. 
     In example operation of the auth-precharge control circuit  2300 , with reference to  FIGS. 18 through 23 , when the write command WR is input, the bank address BA (BA 0  through BA 2 ) for selecting a bank at which the write command WR will be executed may be concurrently (e.g., simultaneously) input to the address buffer  2220 . After a number of clock cycles (e.g., five clock cycles) corresponding to the write latency tWL plus the data burst period tBURST following the write command WR and the bank address BA are input, the delayed write auto-precharge command signal dWAP may be enabled (e.g., set to the first logic level) by the latency control circuit  2250 . Thereafter, a write operation may be performed. 
     In example operation of the auth-precharge control circuit  2300 , with reference to  FIGS. 18 through 23 , the signal dBA_d 1  may be output from the first registers in the respective second register arrays  2321 ,  2322  and  2323  included in the bank address delay unit  2320  by delaying the buffered bank address signal dBA in response to the delayed write auto-precharge command signal dWAP. 
     In example operation of the auth-precharge control circuit  2300 , with reference to  FIGS. 18 through 23 , the first precharge command delay signals dWAP_d 3 , dWAP_d 7  and dWAP_d 11  and the second precharge command delay signal ddWAP may be output from the auto-precharge control circuit  2300  in synchronization with the rising edges of the respective third, seventh, eleventh and twelfth clock cycles, respectively, of the internal clock signal PCLK following the enabling of the delayed write auto-precharge command signal dWAP. 
     In example operation of the auth-precharge control circuit  2300 , with reference to  FIGS. 18 through 23 , the bank delay signal ddBA may be output from the bank address delay unit  2320  by delaying the bank address signal dBA based on the delayed write auto-precharge command signal dWAP and the first precharge command delay signals dWAP_d 3 , dWAP_d 7  and dWAP_d 11 . The bank delay signal ddBA may be output in synchronization with the rising edge of the eleventh clock cycle of the internal clock signal PCLK following the enabling of the bank address signal dBA. 
     In example operation of the auth-precharge control circuit  2300 , with reference to  FIGS. 18 through 23 , in the precharge main signal generator  2330 , the precharge sub-signal BANK may be delayed by the decoder  2331  from the enabling of the bank delay signal ddBA. Accordingly, the precharge main signal PAPB may be output in synchronization with a first rising edge of the internal clock signal PCLK after the enabling of the second precharge command delay signal ddWAP. In an example, the synchronized output may occur 12 clock cycles of the internal clock signal PCLK (e.g., the write recovery time tWR) after the enabling of the delayed write auto-precharge command signal dWAP. 
     In example operation of the auth-precharge control circuit  2300 , with reference to  FIGS. 18 through 23 , the precharge main signal PAPB may be output to a given bank (e.g., bank  3  if dBA=011), which may be selected from among the plurality of banks (e.g., 8 banks) based on the bank address signal dBA. 
     Accordingly, in an example, the auto-precharge control circuit  2300  included in the semiconductor memory device  2200  may include 12 registers within the first register array  2311  and 4 registers included in each of the second register arrays  2321 ,  2322  and  2323 , (e.g., for a total of 24 registers) and may control a write auto-precharge operation. The number of registers included in the auto-precharge control circuit  2300  may be relatively small as compared to the number of registers (e.g., 96 registers) included within a conventional auto-precharge control circuit. 
     As described above, in accordance with example embodiments of the present invention, a latency control circuit may have a “master-slave” structure, such that the number of registers included in a slave unit may be reduced in proportion to a tCCD or a BL. Thus, the total number of registers performing latency control may be reduced, thereby reducing a current consumption and a layout area of semiconductor memory devices. 
     In another example embodiment of the present invention, a write auto-precharge command signal, which may be split at a minimum interval between commands, instead of an internal clock signal may be used in order to delay a bank address signal, thereby reducing a number of registers required to execute a write auto-precharge command. Thus, an area occupied by the registers in a layout may be reduced. Also, a loading of the internal clock signal may be reduced, thereby reducing current or power consumption of a semiconductor memory device. 
     Example embodiments of the present invention being thus described, it will be obvious that the same may be varied in many ways. For example, while the example embodiments of the present invention are described as including particular numbers of registers, banks, etc., it is understood that other example embodiments of the present invention may be directed to any number of banks, registers, etc. Further, it is understood that the above-described first and second logic levels may correspond to a higher level and a lower logic level, respectively, in an example embodiment of the present invention. Alternatively, the first and second logic levels/states may correspond to the lower logic level and the higher logic level, respectively, in other example embodiments of the present invention. 
     Such variations are not to be regarded as a departure from the spirit and scope of example embodiments of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.