Patent Publication Number: US-7911251-B2

Title: Clock signal generating circuit and semiconductor memory apparatus including the same

Description:
CROSS-REFERENCES TO RELATED PATENT APPLICATION 
     The present application claims priority under 35 U.S.C 119(a) to Korean Application No. 10-2009-0040841, filed on May 11, 2009, in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety as set forth in full. 
     BACKGROUND 
     1. Technical Field 
     Embodiments described herein relate generally to a semiconductor memory apparatus and, more particularly, to a clock signal generating circuit and a semiconductor memory apparatus including the same. 
     2. Background 
     A typical semiconductor memory apparatus is configured to receive an external clock signal and generate an internal clock signal having a phase locked through a delay locked loop circuit so that the internal clock signal operates in synchronization with the external clock signal. Further, the semiconductor memory apparatus generates a pair of clock signals having a 180 degree phase difference for high-speed operation and operates in synchronization with the phase difference. 
       FIG. 1  is a block diagram schematically showing a configuration of a conventional clock signal generating circuit. In  FIG. 1 , the clock signal generating circuit includes a delay locked loop circuit (hereinafter, referred to as ‘DLL circuit’)  10 , a main clock buffer  20 , and a sub clock buffer  30 . The DLL circuit  10  generates first and second delay clock signals ‘irclkdll’ and ‘ifclkdll’ using a received external clock signal ‘CLK’. The main clock buffer  20  generates first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ by buffering the first and second delay clock signals ‘irclkdll’ and ‘ifclkdll’. The first and second sub clock buffer  30  generates first and second clock signals ‘rclk’ and ‘fclk’ by buffering the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’, respectively. The first and second clock signals ‘rclk’ and ‘fclk’ are transmitted to circuits that operate in synchronization with the clock signals. 
     As described above, the clock generating circuit includes buffers receiving and buffering clock signals. The buffering operation of the buffers allow a differential clock pair to be generated irrespective of frequency variations of the clock signals. In operation, the main clock buffer  10  is at all times operating in order to buffer the first and second delay clock signals ‘irclkdll’ and ‘ifclkdll’ and generate the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’. A consequence of the continuous operation of the main clock buffer is increased power consumption. 
     SUMMARY 
     Embodiment of the present invention include a clock signal generating circuit of a semiconductor memory apparatus that can generate a clock signal by a scheme that limits power consumption depending on a frequency of an external clock signal and a semiconductor memory apparatus. 
     In one embodiment, a clock signal generating circuit includes a main clock buffering unit configured to output a differential clock signal pair or a single clock signal from first and second delay clock signals depending on the frequency of an external clock signal; and a sub clock receiving the output of the main clock buffering unit and generating first and second clock signals. The manner in which the first and second clock signals is dependent upon whether the differential clock signal pair or the single clock signal has been output by the main clock buffering unit. 
     In another embodiment, a semiconductor memory apparatus includes a DLL circuit configured to receive an external clock signal in order to generate first and second delay clock signals; a frequency detector configured to generate a detection signal by detecting the frequency of the external clock signal; a main clock buffering unit receiving the first and second delay clock signals in order to generate an internal clock signal and providing the internal clock signal as either a differential clock signal pair or a single clock signal in response to the detection signal; and a sub clock buffering unit configured to generate first and second clock signals from the internal clock signal, which is provided as the differential clock signal pair or the single clock signal, in response to the detection signal. 
     In still another embodiment, a semiconductor memory apparatus includes a main clock buffering unit receiving first and second delay clock signals for generating an internal clock signal, and a first sub clock buffering unit configured to generate a first clock signal pair from the internal clock signal applied in the differential clock signal pair when the frequency of the external clock signal is in the first frequency range and generate the first clock signal pair from the internal clock signal applied in the single clock signal when the frequency of the external clock signal is in the second frequency range, and a second sub clock buffering unit configured to generate a second clock signal pair from the internal clock signal applied in the differential clock signal pair when the frequency of the external clock signal is in the first frequency range and generate the second clock signal pair from the internal clock signal applied in the single clock signal when the frequency of the external clock signal is in the second frequency range. 
     These and other features, aspects, and embodiments are described below in the section “Detailed Description.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, aspects, and embodiments are described in conjunction with the attached drawings, in which: 
         FIG. 1  is a block diagram schematically showing a configuration of a conventional clock signal generating circuit; 
         FIG. 2  is a schematic block diagram showing an exemplary clock signal generating circuit according to an embodiment of the present invention; 
         FIG. 3  is a schematic diagram showing an exemplary frequency detector of  FIG. 2  according to an embodiment of the present invention; 
         FIG. 4  is a schematic diagram showing an exemplary main clock buffering unit of the frequency detector of  FIG. 2  according to an embodiment of the present invention; 
         FIG. 5  is a schematic diagram of an exemplary sub clock buffering unit of the frequency detector of  FIG. 2  according to an embodiment of the present invention; 
         FIG. 6  is a timing diagram shown for illustrating the operation of a clock signal generating circuit when an external clock signal has a low frequency according to an embodiment of the present invention; 
         FIG. 7  is a timing diagram shown for illustrating the operation of a clock signal generating circuit when an external clock signal has a high frequency according to an embodiment of the present invention; and 
         FIG. 8  is a schematic diagram showing an exemplary semiconductor memory apparatus according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a schematic diagram of an exemplary clock signal generating circuit according to an embodiment of the present invention. In  FIG. 2 , the clock signal generating circuit  1  is configured to include a frequency detector  100 , a main clock buffering unit  200 , and a sub clock buffering unit  300 . The frequency detector  100  detects the frequency of an external clock signal ‘CLK’ and generates a detection signal ‘det’ according to the frequency. For example, the frequency detector  100  will enable the detection signal ‘det’ when the frequency of the external clock signal ‘CLK’ is in a first frequency range and will disable the detection signal ‘det’ when the frequency of the external clock signal ‘CLK’ is in a second frequency range. Thus, the detection signal ‘det’ is enabled according to the frequency level of the external clock signal ‘clk’. In an embodiment, the first frequency range is a high-frequency range and the second frequency range is a low-frequency range having a frequency range that is lower than that of the first frequency range. In the embodiment shown in  FIG. 2 , the frequency detector  100  is configured to detect the frequency of the external clock signal ‘CLK’ in response to a control signal ‘ctrl’. The control signal ‘ctrl’ will be described below. 
     The main clock buffering unit  200  generates first and second delay clock signals ‘irclkdll’ and ‘ifclkdll’. The first and second delay clock signals ‘irclkdll’ and ‘ifclkdll’ are generated by a delay locked loop (DLL) circuit  10  so as to be delay-locked, thereby allowing the semiconductor memory apparatus to operate in synchronization with the external clock signal ‘CLK’. The first and second delay clock signals ‘irclkdll’ and ‘ifclkdll’ are a differential clock signal pair having a phase difference of 180 degrees. The main clock buffering unit  200  is configured so that it is capable of providing both the differential clock pair and the single clock signal as the internal clock signal. The main clock buffering unit is configured to selectively provide either the differential clock pair or the single clock signal according to the frequency of the external clock signal. More specifically, when the frequency of the external clock signal ‘CLK’ is a high frequency failing within the first frequency range, the main clock buffering unit  200  provides the different clock signal pair as the internal clock signal; and when the frequency of the external clock signal ‘CLK’ has a low frequency that falls within the second frequency range, the main clock buffering unit  200  provides the single clock as the internal clock signal. In further detail, in an embodiment of the present invention, the main clock buffering unit  200  provides first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ as the internal clock signal by buffering the first and second delay clock signals ‘irclkdll’ and ‘ifclkdll’ when the detection signal ‘det’ is enabled indicating a high frequency; and the main clock buffering unit  200  provides the first internal clock signal ‘rclkdll’ as the internal clock signal by buffering the first delay clock signal ‘irclkdll’ when the detection signal ‘det’ is not enabled indicating a low frequency. 
     In the embodiment of the present invention shown in  FIG. 2 , the sub clock buffering unit  300  is configured to receive the internal clock signal from the main clock buffering unit  200  in order to generate the first and second clock signal ‘rclk’ and ‘fclk’. In an embodiment, the sub clock buffering unit  300  is responsive to the detection signal ‘det’ in order to generate the first and second clock signals ‘rclk’ and ‘fclk’ from the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’, which are provided when the different clock signal pair is generated, or the first internal clock signal ‘rclkdll’, which is provided when the single clock signal is generated. More specifically, when the frequency of the external clock signal ‘CLK’ is a high frequency that falls within the range of the first frequency range, the sub clock buffering unit  300  generates the first and second clock signal ‘rclk’ and ‘fclk’ by buffering the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ provided as the different clock pair; and when the frequency of the external clock signal ‘CLK’ is a low frequency falling within the second frequency range, the sub clock buffering unit  300  generates the first and second clock signals ‘rclk’ and ‘fclk’ by buffering the first internal clock signal ‘rclkdll’ provided as the single clock signal. 
     Referring to  FIG. 2 , in an embodiment, the clock signal generating circuit  1  can be configured to further include a repeater  400  that buffers the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ generated by the main clock buffering unit  200 . The repeater  400  is generally constituted by an inverter chain to buffer the respective first and second internal clock signals ‘rclkdll’ and ‘fclkdll’. 
       FIG. 3  is a schematic diagram of an exemplary frequency detector of the clock signal generating circuit of  1  according to an embodiment of the present invention. In the embodiment shown in  FIG. 3 , the frequency detector  100  includes a detection pulse generating unit  110  and a detection signal generating unit  120 . In an embodiment, the detection pulse generating unit  110  generates the detection pulse signal ‘dlyp’ to have a predetermined pulse width ‘ta’ in response to the control signal ‘ctrl’. The predetermined pulse width ‘ta’ of the detection pulse signal ‘dlyp’ can be arbitrarily adjusted depending on application. The control signal ‘ctrl’ can be generated by a DLL reset signal ‘dllrst’ or a clock enable signal ‘clke’ generated from a mode resister set of the semiconductor memory apparatus. Further, the control signal ‘ctrl’ may be generated by a DLL on/off signal ‘dllon/off’. The DLL reset signal ‘dllrst’ is provided after a predetermined time in the mode resister set after the semiconductor memory apparatus is powered up. The clock signal enable signal ‘clke’ distinguishes an active mode from a power down mode of the semiconductor memory apparatus. The DLL on/off signal ‘dllon/off’, which indicates DLL operation on/off of the semiconductor memory apparatus, can be applied from the outside. The control signal ‘ctrl’ can be generated through an OR gate that receives the DLL reset signal ‘dllrst’, the clock signal enable signal ‘clke’, and the DLL on/off signal ‘dllon/off’ and a pulse generator  130  that receives the output of the OR gate. 
     The reason for using the DLL reset signal ‘dllrst’ to generate the control signal ‘ctrl’ is to detect the frequency of the external clock signal ‘CLK’ at the time when the clock signal generating circuit  1  operates after the semiconductor memory apparatus is powered up. The reason for using the clock signal enable signal ‘clke’ to generate the control signal ‘ctrl’ is that the main clock buffering unit  200  provides the single clock signal as the internal clock signal by disabling the detection signal ‘det’ to reduce power consumption in the power down mode, and that the main clock buffering unit  200  selectively provides the differential clock signal pair or the single clock signal as the internal clock signal depending on the frequency of the external clock signal ‘CLK’ to accurately and stably generate the clock signal while reducing the power consumption in the active mode. Further, the reason for using the DLL on/off signal ‘dllon/off’ to generate the control signal ‘ctrl’ is that the main clock buffering unit  200  provides the single clock signal as the internal clock signal to reduce the power consumption when the semiconductor memory apparatus does not perform the DLL operation, and that the main clock buffering unit  200  selectively provides the differential clock signal pair or the single clock signal as the internal clock signal depending on the frequency of the external clock signal ‘CLK’ when the semiconductor memory apparatus performs the DLL operation. Signals for generating the control signal ‘ctrl’ are not limited to the example and may include control signals in regard to all operations of the semiconductor memory apparatus, which are related to a frequency of a clock signal. 
     In an embodiment, the detection signal generating unit  120  receives the detection pulse signal ‘dlyp’ and the external clock signal ‘CLK’ for generating the detection signal ‘det’. The detection signal generating unit  120  is configured to detect whether or not the rising edge of the external clock signal ‘CLK’ is generated during an interval when the detection pulse signal ‘dlyp’ is enabled and enables the detection signal ‘det’ when the rising edge of the external clock signal ‘CLK’ is generated and disables the detection signal ‘det’ when the rising edge of the external clock signal is not generated. 
     Referring to the detection pulse generating unit  110  shown in  FIG. 3 , in an embodiment the detection pulse generating unit  110  includes a delay portion  111 , a PMOS transistor P 1 , an NMOS transistor N 1 , and first and second inverters IV 1  and IV 2 . The delay portion  111  delays the control signal ‘ctrl’ so as to create the predetermined pulse width ‘ta’ of the detection pulse signal ‘dlyp’, that is, an enable interval of the detection pulse signal ‘dlyp’. The PMOS transistor P 1  is responsive to the output of the delay portion  111  and when turned on applies an external voltage VDD to a common node A. The NMOS transistor N 1  is responsive to the control signal ‘ctrl’ and when turned on applies a ground voltage VSS to the common node A. The first and second inverters IV 1  and IV 2  constitute a latch in which input terminals of the respective inverters IV 1  and IV 2  are connected to output terminals of the respective inverters IV 1  and IV 2 , so as to generate the detection pulse signal ‘dlyp’ whose voltage level depends on the voltage level of the common node A. Accordingly, the detection pulse generating unit  110  can generate a detection pulse signal ‘dlyp’ having a predetermined pulse width ‘ta’ as much as the delay amount of the delay portion  111  when the control signal ‘ctrl’ is applied as a pulse. 
     Referring to the detection signal generating unit  120  shown in  FIG. 3 , in an embodiment the detection signal generating unit  120  includes a first NAND gate ND 1 , a third inverter IV 3 , and a flip-flop FF. The first NAND gate ND 1  receives the detection pulse signal ‘dlyp’ and the external clock signal ‘CLK’. The third inverter IV 3  inverts the output of the first NAND gate ND 1 . The output of the third inverter IV 3  is applied to a clock signal terminal of the flip-flop FF, and the detection pulse signal ‘dlyp’ is applied to the data terminal of the flip-flop. The flip-flop FF outputs the detection signal ‘det’ by latching the detection pulse signal ‘dlyp’ inputted into the data terminal at the time when the rising edge of the output of the third inverter IV 3  inputted into the clock signal terminal is generated. Accordingly, the detection signal generating unit  120  is configured to enable the detection signal ‘det’ when the rising edge of the external clock signal ‘CLK’ is generated and disable the detection signal ‘det’ when the rising edge of the external clock signal ‘CLK’ is not generated during the interval in which the detection pulse signal ‘dlyp’ is enabled. 
       FIG. 4  is a schematic diagram of an exemplary main clock buffering unit of the clock signal generating circuit shown in  FIG. 2  according to an embodiment of the present invention. In  FIG. 4 , the main clock buffering unit  200  includes first and second internal clock signal generating units  210  and  220 . The first internal clock signal generating unit  210  receives the first delay clock signal ‘irclkdll’ and the external voltage VDD in order to generate the first internal clock signal ‘rclkdll’. In an embodiment, the first internal clock signal generating unit  210  is configured to include a second NAND gate ND 2  and a plurality of inverters IVn. The first delay clock signal ‘irclkdll’ and the external voltage VDD are applied to the second NAND gate ND 2 . The plurality of inverters IVn are sequentially connected to each other in series and generate the first internal clock signal ‘rclkdll’ by sequentially inverting the output of the second NAND gate ND 2 . Since the second NAND gate ND 2  is applied with the external voltage VDD as one input, the first internal clock signal generating unit  210  generates the first internal clock signal ‘rclkdll’ from the first delay clock signal ‘irclkdll’ at all times irrespective of the frequency of the external clock signal ‘CLK’. 
     The second internal clock signal generating unit  220  receives the second delay clock signal ‘ifclkdll’ and the detection signal ‘det’ in order to generate the second internal clock signal ‘fclkdll’. In an embodiment, the second internal clock signal generating unit  220  includes a third NAND gate and a plurality of inverters IVn. The second delay clock signal ‘ifclkdll’ and the detection signal ‘det’ are applied to the second NAND gate ND 2 . The plurality of inverters IVn are sequentially connected to each other in series and generate the second internal clock signal ‘fclkdll’ by sequentially inverting the output of the third NAND gate ND 3 . In an embodiment, the number of inverters IVn of the second internal clock signal generating unit  220  is the same as the number of inverters IVn of the first internal clock signal generating unit  210 . Since the third NAND gate ND 3  is applied with the detection signal ‘det’, the second internal clock signal generating unit  220  generates the second internal clock signal ‘fclkdll’ from the second delay clock signal ‘ifclkdll’ when the detection signal ‘det’ is enabled and does not generate the second internal clock signal ‘fclkdll’ when the detection signal ‘det’ is disabled. 
       FIG. 5  is a schematic diagram of an exemplary sub clock buffering unit of the clock signal generating circuit shown in  FIG. 2  according to an embodiment of the present invention. In  FIG. 5 , the sub clock buffering unit  300  includes a first clock signal generating unit  310  and a second clock signal generating unit  320 . The first clock signal generating unit  310  receives the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ and the external voltage VDD in order to generate the first clock signal ‘rclk’. In an embodiment, the first clock signal generating unit  310  includes a fourth NAND gate ND 4 , a first NOR gate NOR 1 , a fourth inverter IV 4 , and a fifth NAND gate ND 5 . the first internal clock signal ‘rclkdll’ and the external voltage VDD are applied to the fourth NAND gate ND 4 . The second internal clock signal ‘fclkdll’ and the external voltage VDD are applied to the first NOR gate NOR 1 , and the fourth inverter IV 4  inverts the output of the first NOR gate NOR 1 . The fifth NAND gate ND 5  receives the output of the fourth NAND gate ND 4  and the output of the fourth inverter IV 4  in order to generate the first clock signal ‘rclk’. As such, the first clock signal generating unit  310  generates the first clock signal ‘rclk’ from the first internal clock signal ‘rclkdll’ at all times irrespective of the frequency of the external clock signal ‘CLK’. Since the first clock signal generating unit  310  generates the first clock signal ‘rclk’ from the first internal clock signal ‘rclkdll’ at all times, the first clock signal generating unit  310  may be configured by an embodiment having simpler logic. In the embodiment shown in  FIG. 5 , the logic of the first clock signal generating unit  310  has the same configuration as the logic of the second clock signal generating unit  320  in order to correspond to the loading operation of the second clock signal generating unit  320  to be described below. 
     The second clock signal generating unit  320  receives the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ and the detection signal ‘det’ in order to generate the second clock signal ‘fclk’. In an embodiment, the second clock signal generating unit  320  includes a sixth NAND gate ND 6 , a second NOR gate NOR 2 , a fifth inverter IV 5 , and a seventh NAND gate ND 7 . The second internal clock signal ‘fclkdll’ and the detection signal ‘det’ are applied to the sixth NAND gate ND 6 . The first internal clock signal ‘rclkdll’ and the detection signal ‘det’ are applied to the second NOR gate NOR 2 , and the fifth inverter IV 5  inverts the output of the second NOR gate NOR 2 . The seventh NAND gate ND 7  receives the output of the sixth NAND gate ND 6  and the output of the fifth inverter IV 5  in order to generate the second clock signal ‘fclk’. Accordingly, the second clock signal generating unit  320  generates the second clock signal ‘fclk’ from the second internal clock signal ‘fclkdll’ when the detection signal ‘det’ is enabled and generates the second clock signal ‘fclk’ from the first internal clock signal ‘rclkdll’ when the detection signal ‘det’ is disabled. 
       FIG. 6  is a timing diagram shown for illustrating the operation of a clock signal generating circuit when an external clock signal has a low frequency according to an embodiment; and  FIG. 7  is a timing diagram shown for illustrating the operation of a clock signal generating circuit when an external clock signal has a high frequency according to an embodiment. Referring to  FIGS. 2 to 7 , the operation of the clock signal generating circuit  1  will be described below. When the semiconductor memory apparatus is powered up such that the DLL reset signal ‘dllrst’ is enabled, or when the semiconductor memory apparatus is switched from the power down mode to the active mode such that the clock signal enable signal ‘clke’ is enabled, the control signal ‘ctrl’ is enabled. The detection pulse generating unit  110  of the frequency detector  100  generates a detection pulse signal ‘dlyp’ having a predetermined pulse width ‘ta’ in response to the control signal ‘ctrl’, and the detection signal generating unit  120  of the frequency detector receives the detection pulse signal ‘dlyp’ and the external clock signal ‘CLK’. Since the rising edge of the external clock signal ‘CLK’ having the low frequency is not generated during the interval when the detection pulse signal ‘dlyp’ is enabled, the detection signal ‘det’ is disabled. The main clock buffering unit  200  generates the first internal clock signal ‘rclkdll’ from the first delay clock signal ‘irclkdll’ of the first and second delay clock signals ‘irclkdll’ and ‘ifclkdll’ transmitted from the DLL circuit  10  in response to the disabled detection signal ‘det’. In  FIG. 6 , a delay time ‘tb’ by the main clock buffering unit  200  is shown. The delay time ‘tb’ can be determined by the number of inverters that are included in the main clock buffering unit  200 . The number of inverters may be changed in order to match the application and synchronization timing of the semiconductor memory apparatus. 
     At this time, the second internal clock signal ‘fclkdll’ is not generated due to the disabled detection signal ‘det’; and therefore, the main clock buffering unit  200  provides the first internal clock signal ‘rclkdll’ as the single clock signal. In an embodiment, the repeater  400  can then buffer and transmit the first internal clock signal ‘rclkdll’ to the sub clock buffering unit  300 . The sub clock buffering unit  300  receives the first internal clock signal ‘rclkdll’. The first clock signal generating unit  310  of the sub clock buffering unit  300  generates the first clock signal ‘rclk’ from the first internal clock signal ‘rclkdll’, and the second clock signal generating unit  320  generates the second clock signal ‘fclk’ also from the first internal clock signal ‘rclkdll’ due to the disabled detection signal ‘det’. The first and second clock signals ‘rclk’ and ‘fclk’ are transferred to circuits of the semiconductor memory apparatus, which operate in synchronization with the clock signal. 
     Referring to  FIG. 7 , when the external clock signal ‘CLK’ has a high frequency, a rising edge of the external clock signal ‘CLK’ is generated while the detection pulse signal ‘dlyp’ is enabled, such that the detection signal ‘det’ is enabled. The first internal clock signal generating unit  210  of the main clock buffering unit  200  generates the first internal clock signal ‘rclkdll’ from the first delay clock signal ‘irclkdll’, and the second internal clock signal generating unit  220  generates the second internal clock signal ‘fclkdll’ from the second delay clock signal ‘ifclkdll’ in response to the enabled detection signal ‘det’. Accordingly, when the detection signal ‘det’ is enabled, the main clock buffering unit  200  generates and provides the first and second internal clock signals ‘rclkdll’ and fclkdll’ as the differential clock signal pair. The first clock signal generating unit  310  of the sub clock buffering unit  300  generates the first clock signal ‘rclk’ from the first internal clock signal ‘rclkdll’, and the second clock signal generating unit  320  generates the second clock signal ‘fclk’ from the second internal clock signal ‘fclkdll’ in response to the is enabled detection signal ‘det’. 
     Accordingly, when the external clock signal ‘CLK’ has the low frequency, the main clock buffering unit generates the clock signal by providing the single clock signal as the internal clock signal, thereby reducing the power consumption of the main clock buffering unit and the repeater. Further, when the external clock signal has the high frequency, the main clock buffering unit provides the differential clock pair as the internal clock signal, thereby generating a stable and accurate clock signal even at high frequencies. 
       FIG. 8  is a schematic diagram of an exemplary semiconductor memory apparatus according to an embodiment of the present invention. In  FIG. 8 , a semiconductor memory apparatus can includes a frequency detector  100 , a main clock buffering unit  200 , and first and second sub clock buffering units  300 A and  300 B. In an embodiment, the frequency detector  100  and the main clock buffering unit  200  have the same configuration as the circuits shown in  FIGS. 3 and 4 , and the first and second sub clock buffering units  300 A and  300 B have the same configuration as the circuit shown in  FIG. 5 . Referring to  FIG. 8 , the main clock buffering unit  200  is positioned in a center peripheral circuit region CRERI; the first sub clock buffering unit  300 A is positioned in a left peripheral circuit region DPERIL; and the second sub clock buffering unit  300 B is positioned in a right peripheral circuit region DPERIR. In an embodiment, the sub clock buffering unit  300 A receives the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’, which are generated by the main clock buffering unit  200 , in order to generate a pair of first clock signals ‘rclk_L’ and ‘fclk_L’. Further, the second sub clock buffering unit  300 B also receives the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ in order that the second sub clock buffering unit  300 B can generate a pair of second clock signals ‘rclk_R’ and ‘fclk_R’. The first sub clock buffering unit  300 A, which is positioned at the left side of the center peripheral circuit region, transmits the pair of first clock signals ‘rclk_L’ and ‘fclk_L’ to circuits that operate in synchronization with a clock signal, and the second sub clock buffering unit  300 B, which is positioned at the right side of the center peripheral circuit region, transmits the pair of second clock signals ‘rclk_R’ and ‘fclk_R’ to the circuits that operate in synchronization with the clock signal. 
     In an embodiment, the semiconductor memory apparatus can further include a first repeater  400 A that buffers and provides the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ to the first sub clock buffering unit  300 A and a second repeater  400 B that buffers and provides the first and second internal clock signals ‘rclkdll’ and ‘fclkdll’ to the second sub clock buffering unit  300 B. 
     While certain embodiments have been described above, it will be understood to those skilled in the art that the embodiments described are by way of example only. Accordingly, the device and method described herein should not be limited based on the described embodiments. Rather, the apparatus described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.