Abstract:
A power supplying circuit (PSC) and a phase-change random access memory (PRAM) including the PSC. According to an aspect of the invention, the PSC includes: a first voltage generator configured to output a first voltage to a first terminal; and a second voltage generator configured to output a second voltage to a second terminal, the second voltage generator including: a voltage pump unit configured to output the second voltage based on a clock signal and a pump control signal; a pump output detector coupled to the voltage pump unit, the pump output detector configured to output a pump output detection signal; and a discharging unit coupled to the voltage pump unit, the discharging unit configured to discharge a level of the second voltage to a predetermined level in response to a discharge signal. Embodiments of the invention may prevent write and/or read malfunctions that can occur due to changes in the level of a voltage supplied to PRAM cell blocks.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2007-0115487, filed on Nov. 13, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention provide a power supplying circuit (PSC) and a phase-change random access memory (PRAM) including the PSC. Embodiments of the invention may prevent write and/or read malfunctions that can occur due to changes in the level of a voltage supplied to PRAM cell blocks. 
     According to an aspect of the invention, there is provided a power supply circuit (PSC) adapted for use in a Phase-change Random Access Memory (PRAM). The PSC includes: a first voltage generator configured to output a first voltage to a first terminal; and a second voltage generator configured to output a second voltage to a second terminal, the second voltage generator including: a voltage pump unit configured to output the second voltage based on a clock signal and a pump control signal; a pump output detector coupled to the voltage pump unit, the pump output detector configured to output a pump output detection signal; and a discharging unit coupled to the voltage pump unit, the discharging unit configured to discharge a level of the second voltage to a predetermined level in response to a discharge signal. 
     According to another aspect of the invention, there is provided a semiconductor memory device including: a memory cell array having a plurality of memory blocks; a plurality of switches, each of the plurality of switches connected to a corresponding one of the plurality of memory blocks; a plurality of selectors, each of the plurality of selectors coupled to a corresponding one of the plurality of switches, each of the selectors configured to output a control signal to the corresponding one of the plurality of switches in response to a block selection signal and a discharge success signal; and a power supplying circuit (PSC) coupled to each of the plurality of switches by a first line and a second line, the PSC further coupled to the plurality of selectors by a control line, the PSC configured to output a first voltage to the first line and a second voltage to a second line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a block diagram of a Phase-change Random Access Memory (PRAM) according to an embodiment of the invention; 
         FIG. 2  is a waveform diagram illustrating the operation of the PRAM in  FIG. 1 ; 
         FIG. 3  is a block diagram of a portion of a power supplying circuit (PSC) according to an embodiment of the invention; and 
         FIG. 4  is a timing diagram for signals illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the invention will be described more fully with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. In the drawings, like reference numerals denote like elements. 
       FIG. 1  is a block diagram of a Phase-change Random Access Memory (PRAM) according to an embodiment of the invention. As shown therein, a PRAM semiconductor memory device  100  includes multiple memory blocks BLK 1  through BLKn, switches SW 1  through SWn coupled to the corresponding memory blocks BLK 1  through BLKn, selectors SELL through SELn coupled to the corresponding switches SW 1  through SWn, and a power supplying circuit PSC coupled to the switches SW 1  through SWn and the selectors SEL 1  through SELn. 
     The multiple memory blocks BLK 1  through BLKn may be included in a memory cell array (not shown) of the semiconductor memory device  100 . 
     In operation, the PSC generates a first voltage VPP 1  and a second voltage VPP 2  used in memory cells of the blocks BLK 1  through BLKn. More preferably, the first voltage VPP 1  may be a read voltage and/or a standby voltage, and the second voltage VPP 2  may be a write voltage. Accordingly, the level of the second voltage VPP 2  may be higher than that of the first voltage VPP 1 . The PSC will be described in more detail later. 
     Each of the multiple switches SW 1  through SWn are connected to a first line L 1  and a second line L 2 , the first line L 1  transmitting the first voltage VPP 1  and the second line L 2  transmitting the second voltage VPP 2 . The switches SW 1  through SWn apply at least one of the first voltage VPP 1  and the second voltage VPP 2  to corresponding memory blocks BLK 1  through BLKn in response to corresponding control signals XCON 1  through XCONn output from the corresponding selectors SEL 1  through SELn. More preferably, the switches SW 1  through SWn may be included in corresponding memory blocks BLK 1  through BLKn. 
     As described above, the semiconductor memory device  100  applies a voltage VPP 1  and/or VPP 2  to the cell blocks BLK 1  through BLKn by the power switches SW 1  through SWn. This configuration reduces a load on an output terminal of the PSC. Accordingly, the rising/falling time of the second voltage VPP 2  of the PSC decreases, and less current is consumed. The operating speed may also be improved. 
       FIG. 2  is a waveform diagram illustrating the operation of the PRAM in  FIG. 1 . For purposes of illustration only, we will describe the waveforms with reference to the switch SW 1  and the memory block BLK 1 . 
     Prior to time t 1 , the first voltage VPP 1  that corresponds to a read or standby READ/STBY operation is applied to the first line L 1 . During this same time period, the switch SW 1  connects the first line L 1  to memory block BLK 1 . 
     At time t 1 , the second voltage VPP 2  that corresponds to a write operation WRITE is applied to the second line L 2 , and the switch SW 1  connects the second line L 2  to the memory block BLK 1 . 
     The write operation may be completed at time t 2 . Nevertheless, the switch SW 1  continues to connect the second line L 2  to the memory block BLK 1  until the voltage level of the second line L 2  is discharged to the voltage level of the first voltage VPP 1  (e.g., until time t 3 ). 
     At time t 3 , the first switch SW 1  connects the first line L 1  to the memory block BLK 1 . 
     In the embodiment illustrated in  FIG. 2 , a discharge voltage of the second voltage VPP 2  has the same level as the first voltage VPP 1 ; however, the invention is not limited thereto. For example, in an alternative embodiment, the discharge voltage of the second voltage VPP 2  may have a level associated with an external voltage VCC that is not equal to the first voltage VPP 1 . 
     As illustrated in  FIG. 1 , the operation of the switches SW 1  through SWn are controlled by corresponding control signals XCON 1  through XCONn. The control signals XCON 1  through XCONn are generated by the corresponding selectors SELL through SELn in response to corresponding block selection signals Block  1  through Blockn and a discharge success signal DSC_SCCSS. 
     The block selection signals Block 1  through Blockn may correspond to an external address associated with read and/or write commands. In embodiments of the invention, the selectors SEL 1  through SELn may be included in corresponding switches SW 1  through SWn. 
     With further reference to  FIGS. 1 and 2 , when the write operation is to be performed on memory block BLK 1  (at time t 1 ), the block selection signal Block 1  is activated, the discharge success signal DSC_SCCSS is not activated, the selector SELL outputs the control signal XCON 1  to the switch SW 1  at a first logic level, and the switch SW 1  connects the second line L 2  to the memory block BLK 1 . This same connection state continues between time t 2  and time t 3 . 
     When discharging of the second line L 2  is completed at time t 3 , the discharge success signal DSC_SCCSS is activated, the selector SEL  1  outputs the control signal XCON 1  at a second logic level, and the switch SW 1  connects the first line L 1  to the memory block BLK 1 . 
     Hereinafter, the configuration and operation of the PSC is described in more detail. 
       FIG. 3  is a block diagram of a portion of a power supplying circuit (PSC) according to an embodiment of the invention. 
     The PSC may include a first voltage generator (not shown) and a second voltage generator  300 . The first voltage generator may apply the first voltage VPP 1  to the first line L 1 . The second voltage generator may apply the second voltage VPP 2  to the second line L 2 . For convenience of description,  FIG. 3  illustrates only the second voltage generator  300 . The first voltage generator performs a simple operation, and thus detailed description is omitted. In addition, the configuration and operation of the first voltage generator can be deduced from the configuration and operation of the second voltage generator  300 . 
     Referring to  FIG. 3 , the second voltage generator  300  includes a voltage pump unit  310 , a pump output detector  320 , a discharging unit  330 , and a control unit  340 . 
     The voltage pump unit  310  pumps a clock signal CLK to the second voltage VPP 2  and outputs the second voltage VPP 2  to the second line L 2 . 
     The pump output detector  320  checks the voltage level of an output voltage of the voltage pump unit  310  (e.g., at node N 1 ) and generates a pump output detection signal DET_ACT that indicates a voltage level difference between the output voltage and the second voltage VPP 2 . More preferably, the pump output detector  320  may include a voltage distributor VDIV and a comparator AMP 1 . 
     The voltage distributor VDIV may divide an output voltage of the voltage pump unit  310  into an arbitrary comparison voltage Vcom. The comparator AMP 1  compares the comparison voltage Vcom with a reference voltage VREF 1  in response to an operation enable signal EN_ACT. The pump output detection signal DET_ACT is the result of the comparison. The operation enable signal EN_ACT may be activated during the write operation. 
     The discharging unit  330  may discharge the voltage level of the second voltage VPP 2  to the voltage level of the first voltage VPP 1  in response to a discharge signal P_DSC. More preferably, the discharging unit  330  may include multiple transistors connected in series between the second line L 2  and ground. The multiple transistors may be turned on in response to the discharge signal P_DSC. 
     The discharge signal P_DSC may be activated during the discharging period (e.g., between t 2  and t 3  in  FIG. 2 ). The discharging period may begin when the pump control signal PMP_SCCSS activated. The discharging period may end when the discharge success signal DSC_SCCSS is activated. 
     The control unit  340  may include a first controller (not shown). The first controller (not shown) may generate a pump control signal PMP_SCCSS, which determines whether to pump the voltage pump unit  310 , in response to the pump output detection signal DET_ACT. When the output voltage of the voltage pump unit  310  and the voltage level of the second voltage VPP 2  are equal, the voltage pump unit  310  completes its operation in response to the pump control signal PMP_SCCSS. Otherwise, voltage pump unit  310  continues a pumping operation. 
     The control unit  340  may further include a second controller (not shown). The second controller outputs the discharge success signal DSC_SCCSS or the discharge signal P_DSC according to a logic level of a discharge voltage detection signal DET_DSC. The discharge voltage detection signal DET_DSC may be generated by a discharge detector  350 . 
     The discharge detector  350  checks the voltage level of the second line L 2  during discharging of the second voltage VPP 2  and outputs the discharge voltage detection signal DET_DSC. The discharge detector  350  may include a voltage distributor and a comparator. 
     The discharge voltage detection signal DET_DSC has a first logic level when the voltage level of the second line L 2  has discharged to the same level as a voltage level of the first voltage VPP 1 . The discharge voltage detection signal DET_DSC has a second logic level when the voltage level of the second line L 2  is higher than the voltage level of the first voltage VPP 1 . 
     When the discharge voltage detection signal DET_DSC has the first logic level, the second controller may output the discharge success signal DSC_SCCSS. When the discharge voltage detection signal DET_DSC has the second logic level, the second controller may output the discharge signal P_DSC. 
     The second voltage generator  300  may further include a standby detector  360 . The standby detector  360  compares the output of the voltage pump unit  310  to a comparison voltage VREF  3  and outputs the resulting standby detection signal DET_STB. Thus, the PSC according to the current embodiment of the invention checks the voltage level of the second voltage VPP 2  during a standby period (e.g., after time t 3 ) and controls inappropriate rising of the second voltage VPP 2  during the standby period. 
       FIG. 4  is a timing diagram for signals illustrated in  FIG. 3 . 
     Referring to  FIGS. 3 and 4 , when the write operation is required, the operation enable signal EN_ACT is transitioned to a logic high. In response, the voltage pump unit  310  starts the pumping operation. When the output voltage of the voltage pump unit  310  reaches a target level (the voltage level of the second voltage VPP 2 ), the pump control signal PMP_SCCSS is activated to a logic high and a program (write) operation is performed on the associated memory cells. 
     When the write operation is completed, the pump control signal PMP_SCCSS is transitioned to a logic low. Additionally, the discharge signal P_DSC is transitioned to a logic high so that the second voltage VPP 2  is discharged to the voltage level of the first voltage VPP 1 . When discharging is completed, the discharge success signal DSC_SCCSS is transitioned to a logic high. The write operation for the memory cells is thus completed, and the memory cells are in a read or standby state. 
     While the invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. For instance, In alternative embodiments of the invention, the switches SW 1  through SWn may not be included in corresponding memory blocks. Moreover, in alternative embodiments, the write and read/standby voltages may not be applied according to memory blocks. Furthermore, in alternative embodiments of the invention, discharging may not be performed. Features of the above-described embodiments may therefore be utilized separately or in combinations not expressly illustrated.