Abstract:
The disclosed is a memory such DRAM (dynamic random access memory), particularly an X-address extractor, an X-address extraction method and a memory adaptable to a high speed operation. A DRAM receives X and Y-addresses through an address line. The X-address is input through a command line when an active command is input to the DRAM, and the Y-address is input when a read/write command is input to the DRAM. The X-address abstractor performs a function of extracting the X-address from the X and Y addresses transferred through the address line. A conventional X-address extractor has a problem that the X-address has a different value when a selection signal changes to logic ‘ 0’  from logic ‘ 1’  after an address signal changes to another value from an X-address. The present X-address extractor includes a selection signal generator, a delayer, a latch and an X-address switch, without the problem of the conventional art.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a memory such as a DRAM (dynamic random access memory), and particularly to an X-address extractor and a memory adaptable to a high speed operation.  
         [0003]     2. Discussion of Related Art  
         [0004]     A DRAM receives an X-address and Y-address through an address line. The X-address is input through a command line when an active command is input to the DRAM, and the Y-address is input when a read/write command is input to the DRAM. The X-address abstractor performs a function of extracting the X-address among the X and Y addresses transferred through the address line.  
         [0005]     Hereinafter, a conventional X-address extractor will be described with reference to  FIGS. 1 and 2 .  
         [0006]      FIG. 1  is a block diagram of an X-address abstractor according to a conventional art. In  FIG. 1 , the X-address extractor includes a selection signal generator  10  and an X-address switch  120 .  
         [0007]     The selection signal generator  110  inputs a command signal CMD and then outputs a selection signal SEL. The command signal CMD is output as the selection signal SEL at rising and falling edges of a clock signal CLK.  
         [0008]     The X-address switch  120  receives an address signal ADD and the selection signal SEL and then outputs an X-address signal XADD. When the selection signal SEL is logic ‘ 1 ’, the address signal ADD becomes the X-address signal XADD. When the selection signal SEL is logic ‘ 0 ’, the address signal ADD retains its previous value.  
         [0009]     By such an operation, the X-address extractor extracts the X-address signal XADD from the address signal ADD.  
         [0010]     However, as illustrated in  FIG. 2 , the selection signal SEL is considerably delayed from the command signal CMD because it is operable in sync with the clock signal CLK. As the address signal ADD is transferred to the X-address signal XADD by the selection signal SEL, the X-address signal XADD is much delayed than the address signal ADD. Furthermore, the X-address signal XADD has a different value not the X-address when the selection signal SEL changes to logic ‘ 0 ’ from logic ‘ 1 ’ after the address signal ADD changes to another value from an X-address. Such a problem should be overcome for an improvement of a high speed DRAM because it would be more serious as the DRAM is improved in a higher speed.  
       SUMMARY OF THE INVENTION  
       [0011]     Therefore, the present invention is directed to solve the aforementioned problem, providing an X-address extractor and a memory capable of reducing a delay between an address signal and an X-address signal.  
         [0012]     Another object of the present invention is to provide an X-address extractor and a memory, by which an X-address signal has a value of the X-address even when the selection signal changes to logic ‘ 0 ’ from logic ‘ 1 ’ after an address signal changes to another value from an X-address.  
         [0013]     In order to accomplish the objects, a first aspect of the present invention provides an address extractor for obtaining an output address signal in response to a command signal, an address signal, and a clock signal, comprising: a first element for outputting either a rising edge or a falling edge of the clock signal with a delay for a predetermined time; a second element for outputting a selection signal with a logic value variable in accordance with that the command signal is a predetermined command value; a third element for outputting the selection signal or retaining a previous output value, in accordance with a logic value of the clock signal; a fourth element for outputting the address signal or retaining a previous value, in accordance with a logic value of an output signal of the first element; and a fifth element for outputting an output signal of the fourth element as the output address signal or retaining a previous value, in accordance with a logic value of an output signal of the third element.  
         [0014]     A second aspect of the present invention provides an address extractor for generating an output address signal in response to a command signal transferring a first command and a second command but the first command, an address signal transferring a first address and a second address but the first address, and a clock signal, the address extractor comprising: a first element for outputting a command clock signal and an address clock signal, the command clock signal having a first edge in a period when the command signal is a the first command and a second edge after the period of the first command, the command clock signal having a first logic value before the first edge and a second logic value after the first edge, the address clock signal having a third edge in a period when the address signal is the first address and a fourth edge after the period of the first address, the address clock signal having a third logic value before the third edge and a fourth logic value after the third edge, the second edge being positioned before the fourth edge; a second element for outputting a fifth logic value when the command clock signal is the first logic value and the command signal is the first command, outputting a sixth logic value when the command clock signal is the first logic value and the command signal is the second command, and retaining a previous output value when the command clock signal is the second logic value; a third element for outputting the address signal when the address clock signal is the third logic value and retaining a previous output value when the address clock signal is the fourth logic value; and a fourth element for outputting an output signal of the third element as the output address signal when an output signal of the second element is the fifth logic value and retaining a previous output value when the output signal of the second element is the sixth logic value.  
         [0015]     A third aspect of the present invention provides a memory comprising: a row address extractor either the first or second aspects, for outputting a row address in response to a clock signal, an address signal, and a command signal; a column address generator for creating a column address in response to the address signal and the command signal; a row decoder for selecting a row line in accordance with the row address; a column decoder for selecting a column line in accordance with the column address; and a memory cell array including plurality of memory cells which are readable or writable with data, being designated with a low line selected by the X-address signal and a column line selected by the Y-address signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     A more complete understanding of the present invention may be had by reference to the following description when taken in conjunction with the accompanying drawings in which:  
         [0017]      FIG. 1  is a block diagram of an X-address abstractor according to a conventional art;  
         [0018]      FIG. 2  is a timing diagram of the X-address abstractor according to a conventional art;  
         [0019]      FIG. 3  is a block diagram of an X-address extractor according to a first embodiment of the present invention;  
         [0020]      FIG. 4  is a timing diagram of the X-address extractor according to the first embodiment of the present invention;  
         [0021]      FIG. 5  is a circuit diagram of a clock signal delayer according to the first embodiment of the present invention;  
         [0022]      FIG. 6  is a circuit diagram of a delay circuit according to the first embodiment of the present invention;  
         [0023]      FIG. 7  is a circuit diagram of a selection signal generator according to the first embodiment of the present invention;  
         [0024]      FIG. 8  is a circuit diagram of a selection signal latch according to the first embodiment of the present invention;  
         [0025]      FIG. 9  is a circuit diagram of a clocked inverter according to the first embodiment of the present invention;  
         [0026]      FIG. 10  is a circuit diagram of an address signal latch according to the first embodiment of the present invention;  
         [0027]      FIG. 11  is a circuit diagram of an X-address switch according to the first embodiment of the present invention;  
         [0028]      FIG. 12  is a block diagram of an X-address extractor according to a second embodiment of the present invention;  
         [0029]      FIG. 13  is a timing diagram of the X-address extractor according to the second embodiment of the present invention; and  
         [0030]      FIG. 14  illustrates a memory including the X-address extractor in accordance with the first or second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0031]     Referring now to the drawings wherein like or similar elements are designated with identical reference numerals throughout the several views and wherein various elements depicted are not necessarily drawn to scale. It should be understood that the description of the preferred embodiment is merely illustrative and that it should not be taken in a limiting sense. In the following detailed description, several specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to one skilled in the art that the present invention may be practiced without these specific details.  
         [0032]     Hereinafter, it is described about an X-address extractor according to a first embodiment of the invention in conjunction with  FIGS. 3 and 4 .  FIG. 3  is a block diagram of an X-address extractor according to an embodiment of the present invention, and  FIG. 4  is a timing diagram of the X-address extractor according to an embodiment of the present invention.  
         [0033]     In  FIG. 3 , the X-address extractor includes a clock signal delayer  210 , a selection signal generator  220 , a selection signal latch  230 , an address signal latch  240 , and an X-address switch  250 .  
         [0034]     The clock signal delayer  210  receives a reversed clock signal CLKB and then outputs a delayed-reversed clock signal CLKBD. The clock signal delayer  210  can also delay only the position of a rising edge of the reversed clock signal CLKB.  FIG. 4  shows the reversed clock signal CLKB and the delayed-reversed clock signal CLKBD.  
         [0035]     The selection signal generator  220  outputs a selection signal SEL in response to a command signal CMD. The selection signal SEL retains logic ‘ 1 ’ when the command signal CMD is an active command, while retains logic ‘ 0 ’ when the command signal CMD is not an active command.  FIG. 4  illustrates a timing diagram of the command signal CMD and the selection signal SEL.  
         [0036]     The selection signal latch  230  receives the selection signal SEL and the reversed clock signal CLKB and then outputs a delayed selection signal SELD. If the reversed clock signal CLKB is logic ‘ 1 ’, the delayed selection signal SELD has the value of the selection signal SEL. If the reversed clock signal CLKB is logic ‘ 0 ’, the delayed selection signal SELD retains its previous value.  
         [0037]     The address signal latch  240  receives an address signal ADD and the delayed-reversed clock signal CLKBD and then outputs a delayed address signal ADDD. If the delayed-reversed clock signal CLKBD is logic ‘ 1 ’, the delayed address signal ADDD has the value of the address signal ADD. If the delayed-reversed clock signal CLKBD is logic ‘ 0 ’, the delayed address signal ADDD retains its previous value.  FIG. 4  depicts the states of the address signal ADD, the delayed-reversed clock signal CLKBD, and the delayed address signal ADDD.  
         [0038]     The X-address switch  250  receives the delayed address signal ADDD and the delayed selection signal SELD and then outputs an X-address signal XADD. If the delayed selection signal SEL is logic ‘ 1 ’, the delayed address signal ADDD becomes the X-address signal XADD. If the delayed selection signal SELD is logic ‘ 0 ’, the X-address signal XADD retains its previous value.  FIG. 4  represents the states of the delayed address signal ADDD, the delayed selection signal SELD, and the X-address signal XADD.  
         [0039]     As illustrated in  FIG. 4 , the X-address extractor according to the first embodiment of the present invention normally operates even when the selection signal SEL changes to the inactive logical value from the active logical value after the address signal ADD changes from an X-address to another value. In other words, while in the conventional X-address extractor the X-address signal XADD has another value not an X-address in the case, the X-address extractor according to the first embodiment of the present invention makes enables the X-address signals XADD to have a normal X-address. Moreover, the X-address extractor according to the first embodiment of the present invention has an advantage of enabling an output time of the X-address signal XADD to be earlier than the conventional case, which properly contributes to improving a high speed operation of a memory.  
         [0040]     Hereinafter, it will be described about practical implementations of elements of the X-address extractor according to an embodiment of the present invention, in conjunction with  FIGS. 5 through 11 .  
         [0041]      FIG. 5  illustrates an implementation of the clock signal delayer. Referring to  FIG. 5 , the clock signal delayer outputs the reversed-delayed clock signal CLKBD in response to the reversed clock signal CLKB. The clock signal delayer is formed of a delay circuit  211 , a NAND gate  212 , and an inverter  213 . The reversed clock signal CLKB and a signal output from the delay circuit  211  are applied to an AND logic circuit formed of the NAND gate  212  and the inverter  213 . Then it results in the delayed-reversed clock signal CLKBD with a wider time domain of logical value ‘ 1 ’ while with a narrower time domain of logic ‘ 0 ’.  FIG. 6  is an example of the delay circuit  211  shown in  FIG. 5 . As illustrated in  FIG. 6 , the delay circuit  211  is formed of a plurality of inverters.  
         [0042]      FIG. 7  illustrates an implementation of the selection signal generator. Referring to  FIG. 7 , the selection signal generator receives the command signal CMD formed of /CS, /RAS, /CAS, and /WE and outputs the selection signal SEL. The selection signal generator is comprised of third inverters  221 ,  222 , and  224  and a 4-input NAND gate  223 . If /CS=‘0’, /RAS=‘0’, /CAS=‘1’, and /WE=‘1’, the selection signal SEL becomes logic ‘ 1 ’, i.e., the active logical value.  
         [0043]      FIG. 8  illustrates an implementation of the selection signal latch. Referring to  FIG. 8 , the selection signal latch receives the reversed clock signal CLKB and the selection signal SEL and then outputs the delayed selection signal SELD. The selection signal latch is composed of two inverters  231  and  234 , a first clocked inverter  232 , and a second clocked inverter  233 . An example of the clocked inverters  232  and  233  is illustrated in  FIG. 9 . Referring to  FIG. 9 , the clocked inverter is constructed of two PMOS transistors  236  and  237 , and two NMOS transistors  238  and  239 . In the clocked inverter, an output is a signal reversed from a first input when a second input is logic ‘ 0 ’ and a third input is logic ‘ 1 ’, or conditioned at a high impedance when the second input is logic ‘ 1 ’ and the third input is logic ‘ 0 ’. In  FIG. 8 , if the reversed clock signal CLKB is logic ‘ 1 ’, the first clocked inverter  232  outputs a reversed selection signal because the second input is logic ‘ 0 ’ and the third input is logic ‘ 1 ’. The reversed selection signal is converted to the delayed selection signal SELD after being reversed again. During this, an output of the second clocked inverter  233  is being on a high impedance state. If the reversed clock signal CLKB is logic ‘ 0 ’, the second clocked inverter  233  outputs the reversed selection signal SELD because the second input is logic ‘ 0 ’ and the third input is logic ‘ 1 ’. During this, as the output of the first clocked inverter  232  is in a high impedance state, the delayed selection signal SELD retains its precious value. By the operation of the selection signal latch aforementioned, the delayed selection signal SELD becomes the selection signal SEL when the reversed clock signal CLKB is logic ‘ 1 ’, while retains its previous value when the reversed clock signal is logic ‘ 0 ’.  
         [0044]      FIG. 10  illustrates an implementation of the address signal latch. The address signal latch of  FIG. 10  is constructed as similar to the selection signal latch shown in  FIG. 8 , except its input signals CLKBD and ADD and its output signal ADDD. Therefore, the delayed address signal ADDD becomes the address signal ADD when the delayed-reversed clock signal CLKBD is logic ‘ 1 ’, while retains its previous value when the delayed-reversed clock signal CLKBD is logic ‘ 0 ’.  
         [0045]      FIG. 11  is an implementation of the X-address switch. Referring to  FIG. 1 , the X-address switch receives the delayed selection signal SELD and the delayed address signal ADDD and then outputs the X-address signal XADD. The X-address switch is comprised of four inverters  251 ,  253 ,  254 , and  255 , and a pass transistor  252 . The pass transistor  252  is formed of a PMOS transistor and an NMOS transistor. A source/drain of the PMOS transistor is connected to a source/drain of the NMOS transistor to act as a first source/drain of the pass transistor  252 . The other source/drain of the PMOS transistor is connected to the other source/drain of the NMOS transistor to act as a second source/drain of the pass transistor  252 . When the delayed selection signal SELD becomes logic ‘ 1 ’ of the active logical value, the pass transistor  252  is turned on to transfer the delayed address signal ADDD from the first source/drain to the second source/drain. The delayed address signal ADDD transferred to the second source/drain is converted to the X-address signal after passing through the two inverters  254  and  255 . When the delayed selection signal SELD becomes logic ‘ 0 ’ of the inactive logical value, the pass transistor  252  is turned off to make the X-address signal XADD maintain its previous value by a pair of the inverters  253  and  254 . By the operation of the X-address switch aforementioned, the delayed address signal ADDD becomes the address signal ADD only when the delayed selection signal SELD is logic ‘ 1 ’ as the inactive logical value, while retains its previous value when the selection signal is logic ‘ 0 ’ as the active logical value.  
         [0046]     Hereinafter, it will be described about an X-address extractor in accordance with a second embodiment of the present invention, with reference to  FIGS. 12 and 13 .  FIG. 12  is a block diagram of an X-address extractor according to a second embodiment of the present invention, and  FIG. 13  is a timing diagram of the X-address extractor according to the second embodiment of the present invention.  
         [0047]     The X-address extractor includes a clock signal generator  310 , a selection signal generator  320 , an address signal delayer  330 , and an X-address switch  340 .  
         [0048]     The clock signal generator  310  inputs the clock signal CLK and then outputs a command clock signal CLKCMD and an address clock signal CLKADD.  
         [0049]     The command clock signal CLKCMD has a single edge in a period for which an active command is input by the command signal CMD. The single edge is referred to as a first edge in this embodiment. The first edge is one of rising and falling edges. An edge after the first edge is referred to as a second edge. The second edge is one of rising and falling edges, not the first edge. It is further assumed that a logic value before the first edge is a first logic value and a logic value after the first edge is a second logic value. The first logic value may be one of logic ‘ 1 ’ and ‘ 0 ’, and the second logic value may be, not the first logic value, one of logic ‘ 1 ’ and ‘ 0 ’.  
         [0050]     The address clock signal CLKADD has a single edge in a period for which an X-address is input by the address signal ADD. The single edge is referred to as a third edge in this embodiment. The third edge is one of rising and falling edges. An edge after the third edge is referred to as a fourth edge. The fourth edge is one of rising and falling edges, not the third edge. It is further assumed that a logic value before the first edge is a third logic value and a logic value after the first edge is a fourth logic value. The third logic value may be one of logic ‘ 1 ’ and ‘ 0 ’, and the fourth logic value may be, not the first logic value, one of logic ‘ 1 ’ and ‘ 0 ’.  
         [0051]     The second edge should be positioned prior to the fourth edge. Locations of the first and second edges is preferred to be settled by regarding jitter, setup time, and hold time.  
         [0052]      FIG. 13  illustrates the cooperative relation between the command signal CMD, the command clock signal CLKCMD, the address signal ADD, and the address clock signal CLKADD when the first logic value is logic ‘ 1 ’ and the third logic value is logic ‘ 1 ’.  
         [0053]     The selection signal generator  320  inputs the command clock signal CLKCMD and the command signal CMD and then outputs the selection signal SEL.  
         [0054]     In the condition that the command clock signal CLKCMD is the first logic value, the selection signal SEL is output with a fifth logic value when the command signal CMD is an active command, while with a sixth logic value when the command signal CMD is not an active command. When the command clock signal CLKCMD is the second logic value, the selection signal SEL retains its previous value. The fifth logic value may be one of logic ‘ 1 ’ and ‘ 0 ’, and the sixth logic value may be, not the first logic value, one of logic ‘ 1 ’ and ‘ 0 ’.  FIG. 13  also illustrates the cooperative relation between the command clock signal CLKCMD, the command signal CMD, and the selection signal SEL when the first logic value is logic ‘ 1 ’ and the fifth logic value is logic ‘ 1 ’.  
         [0055]     The address signal delayer  330  receives the address clock signal CLKADD and the address signal ADD and then outputs the delayed address signal ADDD.  
         [0056]     When the address clock signal CLKADD is the third logic value, the address signal ADD directly becomes the delayed address signal ADDD. When the address clock signal CLKADD is the fourth logic value, the delayed address signal ADDD retains its previous value.  FIG. 13  also illustrates the cooperative relation between the address clock signal CLKADD, the address signal ADD, and the delayed address signal ADDD when the third logic value is logic ‘ 1 ’.  
         [0057]     The X-address switch  340  receives the selection signal SEL and the delayed address signal ADDD and then outputs the X-address signal XADD.  
         [0058]     When the selection signal SEL is the fifth logic value, the delayed address signal ADDD directly becomes the X-address signal XADD. When the selection signal SEL is the sixth logic value, the X-address signal XADD retains its previous value.  FIG. 13  also illustrates the cooperative relation between the selection signal SEL, the delayed address signal ADDD, and the X-address signal XADD when the fifth logic value is logic ‘ 1 ’.  
         [0059]     As illustrated in  FIG. 13 , the X-address extractor according to the second embodiment of the present invention normally operates even when the selection signal SEL changes to the inactive logical value from the active logical value after the address signal ADD changes from an X-address to another value. In other words, while in the conventional X-address extractor the X-address signal XADD has another value not an X-address in the case, the X-address extractor according to the second embodiment of the present invention makes enables the X-address signals XADD to have a normal X-address. Moreover, the X-address extractor according to the second embodiment of the present invention has an advantage of enabling an output time of the X-address signal XADD to be earlier than the conventional case, which properly contributes to improving a high speed operation of a memory.  
         [0060]     Hereinafter, it will be explained about a memory including the X-address extractor according to either the first or the second embodiment of the present invention, in conjunction with  FIG. 14 .  FIG. 14  illustrates the memory embedding the present X-address extractor therein.  
         [0061]     Referring to  FIG. 10 , the memory is comprised of an X-address extractor  410  (as same as the described formerly), a Y-address generator  420 , an X-decoder  430 , a Y-decoder  440 , a memory cell array  450 . Here, the X-address denotes a row address and the Y-address denotes a column address. The X-address extractor  410  is that described and illustrated above according to this embodiment of the present invention. The Y-address generator  420  creates the Y-address in response to the command signal CMD and the address signal ADD. The X-decoder  430  selects a low line assigned to the X-address signal XADD and the Y-decoder  440  selects a column line assigned to the Y-address signal YADD. The memory cell array  450  has a plurality of memory cells which are readable or writable with data, being designated with a low line selected by the X-address signal and a column line selected by the Y-address signal.  
         [0062]     With the operation in the memory, data is written into or read from a memory cell in accordance with the X-address signal XADD obtained by the X-address extractor  410  and the Y-address signal YADD provided by the Y-address generator  420 .  
         [0063]     As aforementioned, the X-address extractor and the memory according to the present invention provides an advantage of offering a normal operation even when the selection signal changes to logic ‘ 1 ’ from logic ‘ 0 ’ after an address signal changes from an X-address to another value.  
         [0064]     In addition, the X-address extractor according to the second embodiment of the present invention has an advantage of enabling an output time of the X-address signal XADD to be earlier than the conventional case.  
         [0065]     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as described in the accompanying claims.