Abstract:
An integrated circuit device includes a delay circuit that is configured to delay a clock signal and is further configured to generate an output data signal in response to the delayed clock signal and an input data signal. Multiple devices are configured to respectively receive the output data signal in response to the clock signal.

Description:
RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 2001-8141, filed Feb. 19, 2001, the disclosure of which is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to integrated circuit devices and methods of operating same and, more particularly, to integrated circuit memory devices and methods of operating same. 
     BACKGROUND OF THE INVENTION 
     When applying input signals to multiple semiconductor memory devices, the effects of loading may need to be taken into account. A memory module may use a register to apply input signals to multiple semiconductor memory devices. The register may reduce the distortion in the input signals due to the load of the memory devices; however, because memory devices occupy different positions in a chip and/or a circuit board, the memory devices receive the input signals at different times. This is illustrated, for example, in FIG.  1 . 
     FIG. 1 is a circuit diagram of a conventional memory module in which a register applies input signals to a plurality of semiconductor memory devices, and FIG. 2 is a timing diagram showing the operation of the memory module shown in FIG.  1 . As shown in FIG. 1, a conventional memory module  100  comprises a plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn, a register  120 , and a phase-locked loop  130 . 
     The phase-locked loop  130  generates a plurality of output clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1, which are in phase with each other, in synchronization with an input clock signal CLK. The register  120  generates output signals ACOUT in response to input signals ACIN and in synchronization with the output clock signal OCLK 1 . The register  130  may provide increased driving capability to account for the loading effects of the semiconductor memory devices M 1 , M 2 , . . . , Mn. The semiconductor memory devices M 1 , M 2 , . . . , Mn respectively receive the output signals ACOUT in synchronization with the output clock signals OCLK 2 , . . . , OCLKn+1. 
     Referring now to FIG. 2, transitions in the output signals ACOUT are synchronized with rising edges of the output clock signal OCLK 1 . Thus, as shown in FIG. 2, input signals ACIN are enabled when driven low, and the time that the input signals ACIN are enabled is different from the time that the output signals ACOUT are enabled. The length of time that the output signals ACOUT are enabled is equal to the period of the output clock signal OCLK 1 . 
     As shown in FIG. 2, the output signals ACOUT are delayed for variable lengths of time before they are applied to the plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn. For example, semiconductor memory device Mn is closest to the register  120  and semiconductor memory device M 1  is farthest from the register  120 ; therefore, the output signals ACOUT are received by semiconductor device Mn (illustrated by ACOUT_MN) before the output signals ACOUT are received by the semiconductor device M 1  (illustrated by ACOUT_M 1 ). Because the output signals ACOUT are generated in response to the input signals ACIN and in synchronization with the output clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1, which all have the same phase, the setup and hold times of the output signals ACOUT applied to the semiconductor memory devices M 1 , M 2 , . . . , Mn may not be within desired operating margins for one or more of the semiconductor memory devices M 1 , M 2 , . . . , Mn. The phase of the input clock signal CLK and the output clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1 may be pushed and/or pulled by controlling the capacitance of capacitors CAP 1  and CAP 2  to adjust the setup and hold times; however, the effectiveness of this approach may be limited. The register  120  generates the output signals ACOUT in response to the input signals ACIN and in synchronization with the output clock signal OCLK 1 . Moreover, the output signals OCLK 2 , . . . , OCLKn+1 are in phase with the output clock signal OCLK 1  and are used by the semiconductor memory devices M 1 , M 2 , . . . , Mn to synchronize the reception of the output signals ACOUT. Thus, the plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn may not affected by controlling setup and hold times of the first input signals ACIN. 
     SUMMARY OF THE INVENTION 
     According to embodiments of the present invention, an integrated circuit device comprises a delay circuit that is configured to delay a clock signal and is further configured to generate an output data signal in response to the delayed clock signal and an input data signal. Multiple devices are configured to respectively receive the output data signal in response to the clock signal. The multiple devices may comprise memory devices. 
     In other embodiments of the present invention, the delay circuit comprises a memory unit that is configured to store delay information therein and a delay buffer that is coupled to the memory unit and is configured to generate the delayed clock signal at an output terminal thereof in response to the delay information and the clock signal received at an input terminal thereof. 
     In still other embodiments of the present invention, the delay buffer comprises a plurality of buffers and a plurality of switches that are respectively operable to connect selected ones of the plurality of buffers in series between the input terminal and the output terminal of the delay buffer. 
     In still other embodiments of the present invention, the delay circuit further comprises a demultiplexer circuit that couples the memory unit to the delay buffer and is configured to generate a plurality of switch control signals. Respective ones of the plurality of switches are responsive to the respective ones of the plurality of switch control signals. 
     In still other embodiments of the present invention, the delay circuit further comprises a receiver circuit that is configured to store the input data signal and to generate the output data signal in response to the delayed clock signal and the stored input data signal. 
     In still other embodiments of the present invention, an input terminal is coupled to both the receiver circuit and the memory unit and is configured to receive the input data signal and the delay information therethrough. 
     In still other embodiments of the present invention, a clock generation circuit is configured to generate the clock signal in response to an input clock signal. The clock generation circuit may be a phase locked loop circuit. 
     In further embodiments of the present invention, an integrated circuit device comprises a delay circuit that is configured to receive an input data signal in response to a clock signal and is further configured to generate an output data signal by delaying the input data signal. Multiple devices are configured to respectively receive the output data signal in response to the clock signal. The multiple devices may comprise memory devices. 
     In still further embodiments of the present invention, an integrated circuit device comprises a plurality of delay circuits that are respectively configured to delay a clock signal so as to generate a plurality of output clock signals having differing phases. A storage circuit is configured to generate an output data signal in response to an input data signal and one of the plurality of output clock signals. Multiple devices are configured to respectively receive the output data signal in response to respective other ones of the plurality of output clock signals. 
     Although embodiments of the present invention have been described above primarily with respect to apparatus embodiments, embodiments of methods of operating integrated circuit devices are also provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features of the present invention will be more readily understood from the following detailed description of specific embodiments thereof when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram that illustrates a conventional memory module; 
     FIG. 2 is a timing diagram that illustrates operation of the memory module of FIG. 1; 
     FIG. 3 is a block diagram of an integrated circuit memory module in accordance with embodiments of the present invention; 
     FIG. 4 is a circuit diagram of a delay register for use in the integrated circuit memory module of FIG. 3 in accordance with embodiments of the present invention; 
     FIG. 5 is a timing diagram that illustrates operations of the integrated circuit memory module and the delay circuit of FIGS. 3 and 4 in accordance with embodiments of the present invention; 
     FIG. 6 is a circuit diagram of a delay register for use in the integrated circuit memory module of FIG. 3 in accordance with further embodiments of the present invention; 
     FIG. 7 is a block diagram of an integrated circuit memory module in accordance with further embodiments of the present invention; and 
     FIG. 8 is a circuit diagram of a clock generation circuit for use in the integrated circuit memory module of FIG. 7 in accordance with embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the invention is 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 the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. Like numbers refer to like elements throughout the description of the figures. It will also 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 also be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Referring now to FIG. 3, an integrated circuit memory module  300 , in accordance with embodiments of the present invention, comprises a phase-locked loop (PLL) circuit  330 , a delay register (DREG)  320 , and a plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn. The phase-locked loop circuit  330  generates a plurality of output clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1, which are in phase with each other, in synchronization with an input clock signal CLK. Because the output clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1 are in phase with one another, they may be viewed as a single signal that is distributed to multiple destinations. The delay register  320  generates delayed output signals DACOUT in response to input signals ACIN and in response to the first output clock signal OCLK 1 . The input signals ACIN may be address signals and/or command signals in accordance with embodiments of the present invention. The delay register  320  may provide increased driving capability to account for the loading effects of the semiconductor memory devices M 1 , M 2 , . . . , Mn. The semiconductor memory devices M 1 , M 2 , . . . , Mn respectively receive the delayed output signals DACOUT in synchronization with the output clock signals OCLK 2 , . . . , OCLKn+1. 
     Exemplary operations of the integrated circuit memory module  300 , in accordance with embodiments of the present invention, will now be described with reference to FIG. 3. A capacitor CAP 1  of a feedback loop is adjusted to allow the phase-locked loop  330  to synchronize the input clock signal CLK with the plurality of output clock signals OCLK 1 , OCLK 2 , OCLK 3 , . . . , OCLKn+1 so that the input clock signal CLK and the plurality of output clock signals OCLK 1 , OCLK 2 , OCLK 3 , . . . , OCLKn+1 have the same phase. The delay register  320  receives input signals ACIN, which may have a small margin due to a reduction in setup and/or hold times, in synchronization with the first output clock signal OCLK 1 . In more detail, the delay register  320  delays the first output clock signal OCLK 1  to generate an internal output clock signal, and generates the delayed output signals DACOUT in response to the input signals ACIN and in synchronization with the internal output clock signal. 
     Thus, if the hold time characteristics of the semiconductor memory devices M 1 , M 2 , . . . , Mn are better than the setup time characteristics of the semiconductor memory devices M 1 , M 2 , . . . , Mn (i.e., if the semiconductor memory devices M 1 , M 2 , . . . , Mn may operate normally even though hold time is relatively short), then the delay register  320  may increase the setup time of the delay output signals DACOUT. This may improve the operational stability of the semiconductor memory devices M 1 , M 2 , . . . , Mn. Conversely, the delay register may increase the hold time of the delay output signals DACOUT if the setup time characteristics of the semiconductor memory devices M 1 , M 2 , . . . , Mn are better than the hold time characteristics of the semiconductor memory devices M 1 , M 2 , . . . , Mn. In general, setup and/or hold times of the delayed output signals DACOUT may be adjusted to improve the operational stability of the semiconductor memory devices M 1 , M 2 , . . . , Mn. 
     Accordingly, when the information embodied in the input signals ACIN is provided to the semiconductor memory devices M 1 , M 2 , . . . , Mn through the delayed output signals DACOUT, setup and hold times of the input signals ACIN, which are reduced, may be corrected. As a result, malfunctions in the semiconductor memory devices M 1 , M 2 , . . . , Mn may be reduced. 
     Referring now to FIG. 4, a delay register  400  that may be used to implement the delay register  320  of FIG. 3 comprises a receiver  410  and a delay module  420 , in accordance with embodiments of the present invention. The receiver  410  generates delayed output signals DACOUT 1  and DACOUT 2  in response to input signals ACIN 1  and ACIN 2  and in synchronization with an internal output clock signal OCLKINT. In the exemplary embodiment shown in FIG. 4, the number of input signals ACIN 1  and ACIN 2  is the same as the number of delayed output signals DACOUT 1  and DACOUT 2 . 
     The delay module  420  comprises a ROM  421 , a demultiplexer  423 , and a delay buffer  425 . The ROM  421  receives and stores the ROM input signals ROMIN 1  and ROMIN 2 , which carry information on desired delay time, in response to a write control signal WE. The demultiplexer  423  generates a plurality of switch control signals based on the desired delay time information stored in the ROM  421 . The delay buffer  425  comprises a plurality of buffers BC 1 , BC 2 , . . . BCn and a plurality of switches that are respectively operable in response to the switch control signals output from the demultiplexer  423  to connect selected ones of the plurality of buffers BC 1 , BC 2 , . . . BCn in series between the input terminal and the output terminal of the delay buffer  425 . The delay buffer  425  generates an internal output clock signal OCLKINT, which is variably delayed based on the delay time information stored in the ROM  421 , in response to the output clock signal OCLK 1 . 
     Exemplary operations of the delay register  400 , in accordance with embodiments of the present invention, will now be described with reference to FIG.  4 . If the setup and hold times of the input signals ACIN 1  and ACIN 2  are sufficient to ensure stable operation of an integrated circuit memory module, then the write control signal WE may be driven to a low logic level through the resistor RG to disable operation of the delay module  420  and allow the integrated circuit memory module to operate normally. 
     If, however, the margins of the setup and hold times are reduced to a reduction in setup and hold times of the input signals ACIN 1  and ACIN 2 , then the write control signal WE is driven to a high logic level to allow the ROM  421  to receive the input signals ROMIN 1  and ROMIN 2 , which carry information on the desired delay time. In accordance with embodiments of the present invention, the ROM input signals ROMIN 1  and ROMIN 2  share input pins with the input signals ACIN 1  and ACIN 2 , which are applied to the receiver  410 . The ROM input signals ROMIN 1  and ROMIN 2  are selected when the write control signal WE is at a logic high level and the input signals ACIN 1  and ACIN 2  are selected when the write control signal WE is at a logic low level. It will be understood, however, that, in accordance with other embodiments of the present invention, different logic levels of the write control signal WE may be used to allow the selection of the ROM input signals ROMIN 1  and ROMIN 2  and/or the input signals ACIN 1  and ACIN 2 . 
     The ROM input signals ROMIN 1  and ROMIN 2 , which carry information on the desired delay time for delaying the delayed output signals DACOUT 1  and DACOUT 2  relative to the input signals ACIN 1  and ACIN 2 , respectively, are written to the ROM  421 . A program may provide the delay time information, which is carried by the ROM input signals ROMIN 1  and ROMIN 2 . The ROM  421  is connected to the demultiplexer  423 , which generates output signals corresponding to the desired delay time in response to signals output from the ROM  421 . Signals output from the demultiplexer  423  are applied to the delay buffer  425 , which comprises a plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn. 
     The signals output from the demultiplexer  423  operate a plurality of switches, which are connected to the plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn to connect selected ones of the plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn in series between the input terminal and the output terminal of the delay buffer  425  to delay the internal output clock signal OCLKINT relative to the first output clock signal OCLK 1 . The internal output clock signal OCLKINT is then used to drive the flip-flops FF 1  and FF 2  in the receiver  410 . 
     The receiver  410  generates the delayed output signals DACOUT 1  and DACOUT 2  in response to the input signals ACIN 1  and ACIN 2  and in synchronization with the internal output clock signal OCLKINT. Buffers B 1  and B 2  in the receiver  410  may be used to increase the driving capability of the receiver  410  to account for loading effects of, for example, semiconductor devices that are destined to receive the delayed output signals DACOUT 1  and DACOUT 2 . 
     In other words, the output signals DACOUT 1  and DACOUT 2  are generated in synchronization with the internal output clock signal OCLKINT, which is a delayed version of the first output clock signal OCLK 1 . The ROM input signals ROMIN 1  and ROMIN 2  written to the ROM  421  are adjusted to control the delay between the internal output clock signal OCLKINT and the first output clock signal OCLK 1 . Thus, a reduction in the margin due to a reduction in setup and hold times of the input signals ACIN 1  and ACIN 2  may be corrected to prevent malfunctions in the semiconductor memory devices M 1 , M 2 , . . . , Mn as will now be described with reference to FIG.  5 . 
     Referring now to FIG. 5, in the case where the delayed output signals DACOUT 1  and DACOUT 2  are synchronized with the internal output clock signal OCLKINT, which is a delayed version of the first output clock signal OCLK 1 , setup and hold times may be adjusted to improve the operational stability of an integrated circuit memory module. For example, as shown in FIG. 5, the hold times thmn and thm 1  for semiconductor memory devices M 1  and Mn, respectively, have been increased due to the delay applied to the output signal DACOUT relative to the input signals ACIN 1  and ACIN 2 . It will be understood that, in accordance with embodiments of the present invention, a different delay may be applied to the delayed output signal DACOUT relative to the input signals ACIN 1  and ACIN 2  to increase the setup times tsmn and tsm 1  for the semiconductor memory devices M 1  and Mn, respectively. 
     Referring now to FIG. 6, a delay register  600  that may be used to implement the delay register  320  of FIG. 3 comprises a receiver  610  and a delay module  620 , in accordance with other embodiments of the present invention. The receiver  610  generates internal output signals ACINOUT 1  and ACINOUT 2  in response to input signals ACIN 1  and ACIN 2  and in synchronization with the first output clock signal OCLK 1 . In the exemplary embodiment shown in FIG. 6, the number of input signals ACIN 1  and ACIN 2  is the same as the number internal output signals ACINOUT 1  and ACINOUT 2 . 
     The delay module  620  comprises a ROM  621 , a demultiplexer  623 , a first delay buffer  625  and a second delay buffer  627 . The ROM  621  receives and stores the ROM input signals ROMIN 1  and ROMIN 2 , which carry information on desired delay time, in response to a write control signal WE. The demultiplexer  623  generates a plurality of switch control signals based on the desired delay time information stored in the ROM  621 . The delay buffer  625  comprises a plurality of buffers BC 1 , BC 2 , . . . BCn and a plurality of switches that are respectively operable in response to the switch control signals output from the demultiplexer  623  to connect selected ones of the plurality of buffers BC 1 , BC 2 , . . . BCn in series between the input terminal and the output terminal of the delay buffer  625 . The delay buffer  625  generates the delayed output signal DACOUT 1 , which is variably delayed based on the delay time information stored in the ROM  621 , in response to the internal output signal ACINOUT 1 . The delay buffer  627  comprises a plurality of buffers  2 BC 1 ,  2 BC 2 , . . .  2 BCn and a plurality of switches that are respectively operable in response to the switch control signals output from the demultiplexer  623  to connect selected ones of the plurality of buffers  2 BC 1 ,  2 BC 2 , . . .  2 BCn in series between the input terminal and the output terminal of the delay buffer  627 . The delay buffer  627  generates the delayed output signal DACOUT 2 , which is variably delayed based on the delay time information stored in the ROM  621 , in response to the internal output signal ACINOUT 2 . 
     Exemplary operations of the delay register  600 , in accordance with embodiments of the present invention, will now be described with reference to FIG.  6 . The structure and functionality provided by the delay register  600  are similar to that of the delay register  400  described above. Accordingly, emphasis will be placed on describing differences between operations of the delay register  600  and the delay register  400 . 
     The delay register  400  shown in FIG. 4 delays the first output clock signal OCLK 1  to generate the internal output clock signal OCLKINT and then generates the delayed output signals DACOUT in response to the input signals ACIN and in synchronization with the internal output clock signal OCLKINT. The delay register  600  shown in FIG. 6 generates internal output signals ACINOUT in response to the input signals ACIN and in synchronization with the first output clock signal OCLK 1 . The delay register  600  then generates the delayed output signals DACOUT by variably delaying the internal output signals ACINOUT. 
     The receiver  610  generates the internal output signals ACINOUT 1  and ACINOUT 2  in response to the input signals ACIN 1  and ACIN 2  and in synchronization with the first output clock signal OCLK 1 . Buffers B 1 , B 2  and B 3  in the receiver  610  may be used to increase the driving capability of the receiver  610  with respect to the first output clock signal OCLK 1  and the input signals ACIN 1  and ACIN 2 . 
     The ROM input signals ROMIN 1  and ROMIN 2 , which carry information on the desired delay time for delaying the delayed output signals DACOUT 1  and DACOUT 2  relative to the internal output signals ACINOUT 1  and ACINOUT 2 , respectively, are written to the ROM  621 . A program may provide the delay time information, which is carried by the ROM input signals ROMIN 1  and ROMIN 2 . The ROM  621  is connected to the demultiplexer  623 , which generates output signals corresponding to the desired delay time in response to signals output from the ROM  621 . Signals output from the demultiplexer  623  are applied to the delay buffer  625 , which comprises a plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn, and the delay buffer  627 , which comprises a plurality of buffers  2 BC 1 ,  2 BC 2 ,  2 BC 3 , . . . ,  2 BCn. The number of delay buffers  625  and  627  corresponds to the number of internal output signals ACINOUT 1  and ACINOUT 2 , in accordance with embodiments of the present invention. 
     The signals output from the demultiplexer  623  operate a plurality of switches, which are connected to the plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn to connect selected ones of the plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn in series between the input terminal and the output terminal of the delay buffer  625  to delay the delayed output signal DACOUT 1  relative to the internal output signal ACINOUT 1 . Similarly, the signals output from the demultiplexer  623  operate a plurality of switches, which are connected to the plurality of buffers  2 BC 1 ,  2 BC 2 ,  2 BC 3 , . . . ,  2 BCn to connect selected ones of the plurality of buffers  2 BC 1 ,  2 BC 2 ,  2 BC 3 , . . . ,  2 BCn in series between the input terminal and the output terminal of the delay buffer  627  to delay the delayed output signal DACOUT 2  relative to the internal output signal ACINOUT 2 . 
     The ROM input signals ROMIN 1  and ROMIN 2  written to the ROM  621  may be adjusted to control the timing between the application of the delayed output signals DACOUT to the memory devices M 1 , M 2 , . . . , Mn and the output clock signals OCLK 2 , . . . , OCLKn+1. Thus, a reduction in the margin due to a reduction in setup and hold times of the input signals ACIN 1  and ACIN 2  may be corrected to prevent malfunctions in the semiconductor memory devices M 1 , M 2 , . . . , Mn. 
     Referring now to FIG. 7, an integrated circuit memory module  700 , in accordance with other embodiments of the present invention, comprises a delay phase-locked loop (PLL) circuit  720 , a register  730 , and a plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn. The delay phase-locked loop  720  receives a ROM input signal ROMIN, which carries information on desired delay time, in response to a write control signal WE. The delay phase-locked loop circuit  720  generates a plurality of delay output clock signals DOCLK 1 , DOCLK 2 , . . . , DOCLKn+1, which are out of phase with each other (or delayed relative to each other), in response to an input clock signal CLK. The register  730  generates output signals ACOUT in response to input signals ACIN and in response to the first delay output clock signal DOCLK 1 . The input signals ACIN may be address signals and/or command signals in accordance with embodiments of the present invention. The register  730  may provide increased driving capability to account for the loading effects of the semiconductor memory devices M 1 , M 2 , . . . , Mn. The semiconductor memory devices M 1 , M 2 , . . . , Mn respectively receive the output signals ACOUT in synchronization with the delay output clock signals DOCLK 2 , . . . , DOCLKn+1. 
     Exemplary operations of the integrated circuit memory module  700 , in accordance with embodiments of the present invention, will now be described with reference to FIG.  7 . In embodiments of the present invention described above with reference to FIGS. 3-6, the output signals DACOUT may be variably delayed to control the timing between the application of the delayed output signals DACOUT to the memory devices M 1 , M 2 , . . . , Mn and the output clock signals OCLK 2 , . . . , OCLKn+1. In accordance with embodiments of the present invention illustrated in FIG. 7, the delay output clock signals DOCLK 2 , DOCLK 3 , . . . , DOCLKn+1 of the delay phase-locked loop  720 , each having a different delay time relative to each other, are respectively applied to the plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn. Similar to the embodiments described above with reference to FIGS. 3-6, the integrated circuit memory module  700  may allow a reduction in the margin due to a reduction in setup and hold times of the input signals ACIN to be corrected to prevent malfunctions in the semiconductor memory devices M 1 , M 2 , . . . , Mn, in accordance with embodiments of the present invention. 
     Relative delay time differences between the delay output clock signals DOCLK 1 , DOCLK 2 , DOCLK 3 , . . . , DOCLKn+1 may be determined by an oscilloscope, which measures the time when the output signals ACOUT and the delay output clock signals DOCLK 1 , DOCLK 2 , DOCLK 3 , . . . , DOCLKn+1 reach the plurality of the semiconductor memory devices M 1 , M 2 , . . . , Mn. In other embodiments, the relative delay time differences between the delay output clock signals DOCLK 1 , DOCLK 2 , DOCLK 3 , . . . , DOCLKn+1 may be determined by a middle value of a pass region by writing the output signals ACOUT to and reading them from the plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn with varying delay times. In still other embodiments, the delay time of the delay output clock signals DOCLK 1 , DOCLK 2 , DOCLK 3 , . . . , DOCLKn+1 may be determined by a middle value of a pass region by writing the output signals ACOUT to and reading them from the plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn with varying delay times using a CPU. These methods of determining delay time may also be used in determining the delay information provided to a ROM through input signals ROMIN discussed above. 
     Referring now to FIG. 8, a delay phase-locked loop  800  that may be used to implement the delay phase-locked loop  720  of FIG. 7 comprises a phase detector  801 , a low-pass filter  803 , a voltage control oscillator  805 , and a plurality of delay modules  810 ,  830 , and  840 . The phase detector  801  outputs the phase difference between an input clock signal CLK and a voltage controlled oscillation signal VCOS. The low-pass filter  803  passes a phase difference signal output from the phase detector  801  to generate a control voltage CV. The voltage control oscillator  805  generates the voltage controlled oscillation signal VCOS and clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1 in response to the control voltage CV. In accordance with embodiments of the present invention, the clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1 have the same phase. The plurality of delay modules  810 ,  830 , and  840  generate delay output clock signals DOCLK that each have a different delay time relative to each other in response to a ROM input signal ROMIN and output clock signals OCLK. 
     The delay modules  810 ,  830 , and  840  have the same structure; therefore, only delay modules  810  will be described. The delay module  810  comprises a ROM  821 , a demultiplexer  823 , and a delay buffer  825 . The ROM  821  receives and stores the ROM input signals ROMIN, which carry information on desired delay time, in response to a write control signal WE. The demultiplexer  823  generates a plurality of switch control signals based on the desired delay time information stored in the ROM  821 . The delay buffer  825  comprises a plurality of buffers BC 1 , BC 2 , . . . BCn and a plurality of switches that are respectively operable in response to the switch control signals output from the demultiplexer  823  to connect selected ones of the plurality of buffers BC 1 , BC 2 , . . . BCn in series between the input terminal and the output terminal of the delay buffer  825 . The delay buffer  825  generates the delay output clock signal DOCLK 2 , which is variably delayed based on the delay time information stored in the ROM  821 , in response to the clock signal OCLK 2 . 
     Exemplary operations of the delay phase-locked loop  800 , in accordance with embodiments of the present invention, will now be described with reference to FIG.  8 . The phase detector  801  outputs the phase difference between an input clock signal CLK and a voltage controlled oscillation signal VCOS. The low-pass filter  803  passes a phase difference signal output from the phase detector  801  to generate a control voltage CV. The voltage control oscillator  805  generates the voltage controlled oscillation signal VCOS and clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1 in response to the control voltage CV. In accordance with embodiments of the present invention, the clock signals OCLK 1 , OCLK 2 , . . . , OCLKn+1 have the same phase. 
     The ROM input signal ROMIN, which carries information on the desired delay time for delaying the delay output clock signal DOCLK 2  relative to the clock signal OCLK 2 , are written to the ROM  821 . A program may provide the delay time information, which is carried by the ROM input signals ROMIN. The ROM input signal ROMIN is a series signal, which determines different delay times for each of the delay modules  810 ,  830 , and  840 . The ROM  821  is connected to the demultiplexer  823 , which generates output signals corresponding to the desired delay time in response to signals output from the ROM  821 . Signals output from the demultiplexer  823  are applied to the delay buffer  825 , which comprises a plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn. 
     The signals output from the demultiplexer  823  operate a plurality of switches, which are connected to the plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn to connect selected ones of the plurality of buffers BC 1 , BC 2 , BC 3 , . . . , BCn in series between the input terminal and the output terminal of the delay buffer  825  to delay the delay output clock signal DOCLK 2  relative to the clock signal OCLK 2 . 
     Unlike the embodiments of the present invention described above with reference to FIGS. 3-6, the ROM input signal ROMIN does not share input pins with the input signals ACIN; therefore, and the delay phase-locked loop  800  uses a separate terminal to receive the ROM input signal ROMIN. 
     The delay phase-locked loop  800  delays the delay output clock signals DOCLK 1 , DOCLK 2 , DOCLK 3 , . . . , DOCLKn+1 relative to each other, which are then applied to the plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn and the register  730 . This may allow setup and hold times, which vary when the output signals ACOUT are applied to the semiconductor memory devices M 1 , M 2 , . . . , Mn in synchronization with clock signals that are all in phase with one another, to be corrected to provide a large enough margin for the semiconductor memory devices M 1 , M 2 , . . . , Mn and reduce malfunctions in the plurality of semiconductor memory devices M 1 , M 2 , . . . , Mn. 
     As described above, the operation margin of a plurality of semiconductor memory devices may be reduced due to a reduction in setup and hold times of the input signals provided to the plurality of semiconductor memory devices. In accordance with embodiments of the present invention, however, the input signals may be generated in synchronization with a clock signal that is delayed relative to the clock signals used to drive the plurality of semiconductor memory devices or the clock signals used to drive the plurality of semiconductor devices may be generated to be out of phase with one another (or be delayed relative to each other) to reduce malfunctions in the plurality of semiconductor memory devices. 
     In concluding the detailed description, it should be noted that many variations and modifications can be made to the preferred embodiments without substantially departing from the principles of the present invention. All such variations and modifications are intended to be included herein within the scope of the present invention, as set forth in the following claims.