Abstract:
A delay locked loop (DLL) circuit for a synchronous dynamic random access memory (SDRAM) enables a more stable operation when the semiconductor operates in a power-down mode for low power. The present invention can prevent a phase update operation from being interrupted when the DLL circuit enters a power-down mode. For the above purpose, an off operation of a clock buffer is delayed until a clock signal notifying a final period of the phase update is activated.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to semiconductor design technologies; and more particularly, to a delay locked loop (DLL) for a synchronous dynamic random access memory (SDRAM), which enables a more stable operation when the semiconductor operates in a power-down mode for low power.  
       DESCRIPTION OF RELATED ARTS  
       [0002]     A synchronous semiconductor memory device such as double data rate (DDR) SDRAM performs data transmission with external devices by using an internal clock signal that is locked in synchronism with an external clock signal from an external device such as a memory controller. This is because temporal synchronization between a reference clock signal and data is very important for stable data transmission between the memory and the memory controller. In other words, for stable data transmission, data should be correctly arranged at the edge or center of a clock by reverse-compensating a time taken to carry the data on a bus from the clock of respective elements that transmit the data. Clock synchronization circuits for this purpose include a phase locked loop (PLL) circuit and a DLL circuit. For example, if a frequency of an external clock signal is different from that of an internal clock signal, the PLL circuit is mainly employed due to a need for a multiple frequency function. Otherwise, if a frequency of the external clock signal is identical to that of the internal clock signal, the DLL circuit is mostly utilized.  
         [0003]     The DLL circuit creates an internal clock signal through compensation for clock delay components that occur during the course of conveying an output clock signal to a data output stage within a semiconductor memory device and thus allows the clock signal used for input/output of final data to be synchronized with an external clock signal. In this DLL circuit, advantages are that noise is minimal and small-sized circuit implementation is possible, compared to the PLL circuit. Because of such merits, the DLL circuit is generally adopted in the semiconductor memory device as the synchronization circuit. A widely used DLL circuits a register controlled DLL circuit, provided with a register that can store a locked delay value, and which keeps the value in the register when power is interrupted. Time needed for an initial clock locking is reduced by loading the locked delay value stored in the register for use when power is resumed for the clock locking.  
         [0004]      FIG. 1  is a block diagram of a conventional DLL circuit.  
         [0005]     As shown therein, the conventional DLL circuit generally includes a clock buffer controller  10 , a clock buffer  20 , first and second phase delay &amp; delay controllers  30  and  40 , a pre-duty cycle correction (DCC) unit  50 , a DCC unit  60 , a delay replica modeling unit  70 , a phase comparator  80 , a mode generator  90 , a DLL controller  100 , A clock generator  110 , and an output driver  120 .  
         [0006]     Specifically, the clock buffer controller  10  receives an inverted signal CKEB_COM of a clock enable signal, a signal SAPD having power-down mode information of mode register setting (MRS) and a signal RASIDLE with precharge information, and produces a clock buffer enable signal CLKBUF_ENB to control the clock buffer  20 . For low power operation, the DRAM enters the power-down mode in response to the clock enable signal CKE of logic low value when no read/write operations are made therein. At this time, the clock buffer  20  generates no internal clock signals, thus turning the power off for current status storage by the DLL circuit.  
         [0007]     The clock buffer  20 , in response to the clock buffer enable signal CLKBUF-ENB, receives and buffers an external clock signal, and outputs first and second internal clock signals CLKIN 1  and CLKIN 2  of in-phase, a reference internal clock signal REFCLK and a third internal clock signal CONTCLK.  
         [0008]     The first phase delay &amp; delay controller  30  delays a phase of the first internal clock signal CLKIN 1  and outputs a delayed signal as a first internal delay clock signal MIXOUT_R, in response to first and second locked state signals FAST_MODE_END and LOCK_STATE provided from the mode generator  90 .  
         [0009]     Similarly, the second phase delay &amp; delay controller  40  delays a phase of the second internal clock signal CLKIN 2  and provides a delayed signal as a second internal delay clock signal MIXOUT_F, in response to third and fourth locked state signals FAST_MODE_ENDF and LOCK_STATEF from the mode generator  90 .  
         [0010]     The pre-DCC unit  50  buffers the first internal delay clock signal MIXOUT_R and outputs it as a rising clock RCLK; and also buffers and inverts the second internal delay clock signal MIXOUT_F, and outputs an inverted signal as a falling clock FCLK. Here, duties of the rising clock RCLK and the falling clock FCLK are complementary in value. That is, if a high pulse width of the external clock is wide, a high pulse width of the rising clock RCLK is wide, while a high pulse width of the falling clock FCLK is narrow.  
         [0011]     The DCC unit  60  accepts the rising clock RCLK and the falling clock FCLK of which clock duties are complementary, and corrects the duty of each clock to provide them as a rising feedback clock IFBCLKR and a falling feedback clock IFBCLKF.  
         [0012]     The delay replica modeling unit  70  models the rising feedback clock IFBCLKR and the falling feedback clock IFBCLKF from the DCC unit  60  to compensate for delay factors that occur before signals arrive at the phase delay section after receipt of clock from the exterior of chip and until dispatching an output clock of the phase delay section to the exterior of chip. Through such modeling, a compensated rising feedback clock IFBCLKR and a compensated falling feedback clock FBCLKF, which compensate for a time difference between the external clock and the actual internal clock, are derived. The correct delay factors are used to determine a distorted value as a performance of the DLL circuit. For the delay replica modeling unit  70 , there are methods of shrinking, simplifying, and using basic circuits as they are. In fact, the delay replica modeling unit  70  beforehand models the clock buffer, a DLL clock driver, an R/F divider, and an output buffer as it is.  
         [0013]     The phase comparator  80  compares each of the compensated rising feedback clock FBCLKR and the compensated falling feedback clock FBCLKF from the delay replica modeling unit  70  with the reference internal clock signal REFCLK from the clock buffer  20  to produce phase detection signals. Normally, the external clock is divided by a divider for the comparison so that power consumption of the DLL circuit can be reduced.  
         [0014]     The mode generator  90  generates the first and second locked state signals FAST_MODE_END and LOCK_STATE, indicating that a delay locking of the clock in the first phase delay &amp; delay controller  30  has been established, by using a first location comparison control signal FINE, a first coarse delay control signal FM_PDOUT and a first fine delay control signal COARSE, provided from the phase comparator  80 . Also, it produces the third and fourth locked state signals FAST_MODE_ENDF and LOCK_STATEF, denoting that a delay locking of clock in the second phase delay &amp; delay controller  40  has been made, based on a second location comparison control signal FINEF, a second coarse delay control signal FM_PDOUTF and a second fine delay control signal COARSEF from the phase comparator  80 .  
         [0015]     The speed of phase update by the DLL circuit is varied depending on output logical values of the first to fourth locked state signals output from the mode generator  90 . The phase update implies that a phase of each of the rising feedback clock FBCLKR and the falling feedback clock FBCLKF compensated by the DLL circuit is compared with that of the reference internal clock signal REFCLK to be decided, to continuously track a phase difference therebetween. Examples are introduced below.  
         [0016]     If the phase difference between each of the compensated rising feedback clock FBCLKR and falling feedback clock FBCLKF and the reference internal clock signal REFCLK is large, the first and third locked state signals FAST_MODE_END and FAST_MODE_ENDF are kept at a logic low value. Then, the first and second phase delay &amp; delay controllers  30  and  40 , which receive the signals, shift the phases of the compensated rising feedback clock FBCLKR and falling feedback clock FBCLKF by a four-unit delay at a time, respectively. If the phase difference is less than the four-unit delay, the first and third locked state signals FAST_MODE_END and FAST_MODE_ENDF are maintained at a logic high value. The first and second phase delay &amp; delay controllers  30  and  40  shift the phases of the compensated rising feedback clock FBCLKR and falling feedback clock FBCLKF by a two-unit delay at a time, respectively. If the phase difference is smaller than a one-unit delay, the first and second phase delay &amp; delay controllers  30  and  40  fine-tune the phases of the feedback signals while the second and fourth locked state signals LOCK_STATE and LOCK_STATEF rise from a logic low to a logic high. After that, if the phases become in-phase, the DCC unit  60  is enabled by a phase update locking information signal DCC_ENB generated by itself and the phase update process is completed. In this process, the compensated rising feedback clock FBCLKR and falling feedback clock FBCLKF are controlled in different manner but in the same manner after the phase update has been locked.  
         [0017]     The DLL controller  100  provides a reset signal RESET to control the operation of the DLL circuit in response to a DLL reset signal DLL_RESETB and a DLL inactivation signal DIS_DLL transmitted from the exterior of the memory.  
         [0018]     The clock generator  110  receives the third internal clock signal CONTCLK from the clock buffer  20  and the phase update locking information signal DCC_ENB from the DCC UNIT  60  and generates a first clock PULSE 2  indicating a start of a phase update period at the time of transitioning from the power-down mode and a second clock PULSE 8 _ 11  indicating an end thereof.  
         [0019]     The output driver  120  buffers and outputs the rising feedback clock IFBCLKR and falling feedback clock IFBCLKF from the DCC unit  60 .  
         [0020]     In the DLL circuit having the structure as shown in  FIG. 1 , in case where the DLL circuit slowly escapes from the power-down mode, it is turned off at the time of entering into a precharge power-down mode. Thus, the internal clock of the DLL circuit becomes on/off by controlling on/off operations of the clock buffer  20 . If the internal clock of the DLL circuit turns off, internal operation of the DLL circuit is temporarily halted and then resumed after leaving the precharge power-down mode. In this case, the following problems can occur.  
         [0021]     Firstly, there may be a case in which a phase of the phase delay section is updated by using data, which is compared prior to entering into the precharge power-down mode according to the precharge power-down mode entry timing, after termination of the precharge power-down mode.  
         [0022]     Secondly, the phase update may be conducted with wrong information, which is issued by a faster input of the reference internal clock signal REFCLK to the phase comparator  80 , rather than simultaneous input of the internal clock signal and the compensated rising feedback clock FBCLKR and falling feedback clock FBCLKF thereto, for the reason that the internal clock of the DLL circuit comes on after termination of the precharge power-down mode.  
       SUMMARY OF THE INVENTION  
       [0023]     It is, therefore, an object of the present invention to provide a DLL device and a method for a semiconductor memory device which allows a clock buffer of a DLL circuit to be turned off after an ongoing phase update is completed when the DLL enters a power-down mode entry in a normal mode where the phase update is being performed.  
         [0024]     In accordance with one aspect of the present invention, there is provided a synchronous memory device having a normal mode and a power-down mode including: a DLL for generating a DLL clock based on locking information frozen at the time of termination of the power-down mode, wherein a phase update is not performed during the power-down mode; a clock generator for producing clocks indicating a start and an end of a phase update period during the normal mode; and a control unit for halting the phase update operation of the DLL after the clock indicating the end of the phase update period is input to have a margin of a phase update time when entering into the power-down mode from the normal mode.  
         [0025]     In accordance with another aspect of the present invention, there is provided a DLL circuit including: a power-down mode controller for generating a first control signal to determine whether the DLL circuit enters or leaves a power-down mode; a clock generator for producing a first clock indicating a start of a phase update period and a second clock indicating an end of the phase update period; a clock buffer controller for receiving the first control signal and generating a second control signal in response to toggling of the second clock; a clock buffer for buffering an external clock and generating an internal clock in response to the second control signal; a phase update section for performing the phase update based on the internal clock; and a DLL controller for generating a reset signal to control the operation of DLL the circuit in response to a DLL reset signal and a DLL inactivation signal transmitted from the exterior of the memory.  
         [0026]     The present invention can prevent an ongoing phase update operation from being abruptly interrupted by delaying an off time of a clock buffer to allow the clock buffer to be turned off after the phase update is completed when the DLL enters a power-down mode entry in a normal mode where the phase update is being performed. For the above purpose, the present invention employs an effective scheme that uses a final signal PULSE 8 _ 11  of a phase update period and delays an off time of the clock buffer until the final signal is activated, and is implemented in the clock buffer controller. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:  
         [0028]      FIG. 1  is a block diagram of a configuration of a conventional DLL circuit;  
         [0029]      FIG. 2  is a block diagram of a configuration of a DLL circuit in accordance with an embodiment of the present invention;  
         [0030]      FIG. 3  is a schematic circuit diagram of a power-down mode controller and a clock buffer controller in accordance with an embodiment of the present invention; and  
         [0031]      FIG. 4  is a circuit diagram for describing another embodiment of the power-down mode controller and the clock buffer controller of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     Hereinafter, a delay locked loop (DLL) circuit in accordance with the present invention will be set forth in detail with reference to the accompanying drawings so that the invention can be readily carried out by those in the art to which the invention pertains.  
         [0033]      FIG. 2  is a block diagram of a configuration of a DLL circuit in accordance with an embodiment of the present invention.  
         [0034]     Referring to  FIG. 2 , the inventive DLL circuit has a normal mode and a power-down mode for use in a synchronous memory device. A DLL  300  generates a DLL clock based on locking information frozen at the time of termination of the power-down mode, wherein phase update is not performed during the power-down mode. A clock generator  400  generates clocks PULSE 2  and PULSE 8 _ 11 , indicating a start and an end of a phase update period during the normal mode. A control unit  200  for halts the phase update operation of the DLL  300  after the clock PULSE 8 _ 11 , indicating the end of the phase update period is input, to provide a margin of phase update time when entering into the power-down mode from the normal mode.  
         [0035]     More specifically, the control unit  200  is composed of a power-down mode controller  220  for generating a first control signal BUF_ENB to decide whether the power-down mode is entered or terminated and a clock buffer controller  240  for receiving the first control signal BUF_ENB and providing a second control signal CLKBUF_ENB in response to toggling of the second clock PULSE 8 _ 11 .  
         [0036]     The DLL  300  is provided with a clock buffer  310  that buffers an external clock and generates an internal clock REFCLK in response to the second control signal CLKBUF_ENB, and phase update circuits  320  to  370  for performing the phase update operation based on the internal clock REFCLK.  
         [0037]      FIG. 3  is a schematic circuit diagram of the power-down mode controller  220  and the clock buffer controller  240  in accordance with an embodiment of the present invention.  
         [0038]     Referring to  FIG. 3 , the clock buffer controller  240  includes a signal delay circuit  242  for receiving the first control signal BUF_ENB and providing a signal that is generated by delaying the first control signal BUF_ENB by a predetermined time period in response to toggling of the second clock PULSE 8 _ 11 , a logic circuit  244  for taking an output signal BUF_ENB 8 _ 11  of the signal delay circuit  242  and the first control signal BUF_ENB and generating the second control signal CLKBUF_ENB, and a reset circuit  246  for receiving the reset signal RESET and an inverted signal BUF_EN of the first control signal and controlling an operation of the signal delay circuit  242 .  
         [0039]     Among the components of the clock buffer controller  240 , the signal delay circuit  242  is provided with a D Flip/Flop (F/F) in which the first control signal BUF_ENB is input to a data input D, the second clock PULSE 8 _ 11  to a clock input C, and the output signal of the reset circuit to a reset input. The D F/F is composed of a plurality of D F/Fs connected in series although not shown in the figure. The logic circuit  244  includes a first NAND gate NAND 1  for receiving and NAND-operating the output signal BUF_ENB 8 _ 11  of the signal delay circuit  242  and the first control signal BUF_ENB to output a NAND-operated signal, and a first inverter INV 1  for inverting the output signal of the first NAND gate NAND 1  to provide the second control signal CLKBUF_ENB.  
         [0040]     The reset circuit  246  includes a second inverter INV 2  for inverting and outputting the reset signal RESET, a delay line block for receiving and delaying an inverted signal BUF_EN of the first control signal for a predetermined time period, a third inverter INV 3  for inverting and outputting an output signal of the delay line block, a second NAND gate NAND 2  for receiving and NAND-operating an output signal of the third inverter INV 3  and the inverted signal BUF_EN of the first control signal to provide an NAND-operated signal, and a third NAND gate NAND 3  for taking and NAND-operating an output signal of the second inverter INV 2  and the output signal of the second NAND gate NAND 2  to produce an internal reset signal TMP_RESET to control an operation of the signal delay circuit  242 .  
         [0041]     The power down mode controller  220  includes a NAND gate NAND 4  for receiving and NAND-operating an inverted signal CKEB_COM of the clock enable signal CKE, power-down mode information SAPD of mode register setting (MSR) and precharge information RASIDLE to provide a NAND-operated signal, and an inverter INV 4  for inverting the output signal BUF_EN of the NAND gate NAND 4  to output the first control signal BUF_ENB.  
         [0042]     Description of the flow of signals of the control unit  200 is as follows. At the power-down mode controller  220 , when the clock enable signal CKE has a second logic value, its inverted signal CKEB_COM and the power-down mode information of MRS are of a first logic value, respectively. When the precharge information RASIDLE has a first logic value, the first control signal BUF_ENB of a first logic value is output.  
         [0043]     The signal delay circuit  242  is not reset but can operate when the inverted signal BUF_EN of the first control signal and the reset signal RESET of the reset circuit  246  have a second logic value, respectively.  
         [0044]     At the signal delay circuit  242 , although the first control signal BUF_ENB of first logic value is applied to the data input of the D F/F, the first control signal BUF_ENB is delayed until the second clock PULSE 8 _ 11  applied to the clock input of the D F/F changes from the second logic value to the first logic value, thus securing a sufficient time to do the phase update.  
         [0045]     If the phase update is completed, then the locking information of the DLL circuit is formed and at the same time the second clock PULSE 8 _ 11  transitions to the first logic value. If the second clock PULSE 8 _ 11  assumes the first logic value, the first control signal BUF_ENB, which is being delayed by the D F/F, is provided as the output signal BUF_ENB 8 _ 11  of the signal delay circuit  242 . Then, the logic circuit  244  receives the output signal BUF_ENB 8 _ 11  of the signal delay circuit  242  and the first control signal BUF_ENB and outputs the second control signal CLKBUF_ENB of the first logic value. In response to the second control signal CLKBUF_ENB of the first logic value, the operation of the clock buffer  310  turns off. Thus the internal clock of the DLL circuit turns off, and the DLL circuit enters the power-down mode.  
         [0046]      FIG. 4  is a circuit diagram for describing another embodiment of the clock buffer controller  240  of the present invention.  
         [0047]     With reference to  FIG. 4 , the present invention allows the signal BUF_ENB_ 11  issued from the final output stage of the signal delay circuit to assume the first logic value after the second clock PULSE 8 _ 11  is issued n times (n being a natural number greater than 1) since the clock enable signal CKE assumes the second logic value. By doing so, the present invention can compensate the phase update n times by causing the second control signal CLKBUF_ENB to have the first logic value. Thus the clock buffer of the DLL circuit will be off after performing the phase update n times.  
         [0048]     The above described invention avoids phase update with wrong information caused by time difference of the internal clock signal REFCLK and the feedback signal FBCLK that are input to the phase comparator for the reason that the clock buffer of the DLL circuit is on. The phase update is performed with the current information immediately after an ongoing phase update is completed when the clock buffer is turned off when it enters the power-down mode.  
         [0049]     It should be noted that the logic gates and transistors illustrated in the embodiment may be implemented differently in type and location based on polarities of signals applied thereto.  
         [0050]     The present application contains subject matter related to Korean patent application No. 2005-91555 &amp; 2005-117124, filed in the Korean Patent Office on Sep. 29, 2005 &amp; Dec. 2, 2005, the entire contents of which are incorporated herein by reference.  
         [0051]     While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.