Abstract:
A sense amplifier and method thereof are provided. The sense amplifier includes first and second transistors coupled to first and second bit lines, respectively. The first and second transistors are configured to connect the first and second bit lines to a differential amplifier during a first state (e.g., when a differential voltage is present on the first and second bit lines and prior to a sense signal transition) and to isolate the first and second bit lines from the differential amplifier during a second state (e.g., after the sense signal transition). The sense amplifier further includes a third transistor configured to deactivate the differential amplifier during the first state and configured to activate the differential amplifier during the second state.

Description:
FIELD OF DISCLOSURE 
       [0001]    Disclosed embodiments are related to sense amplifiers circuits and methods. In particular the embodiments relate to dual sensing current latched sense amplifiers. 
       BACKGROUND 
       [0002]    Memory devices conventionally include arrays of bit cells that each store a bit of data. Each data bit can represent a logical low (“0”) or a logical high (“1”), which may correspond to a state of the bit cell. For example, during a read operation a voltage level at a selected bit cell close to ground may be representative a logical low or “0” and a higher voltage level may be representative of a logical high or “1.” Bit lines are coupled to various bit cells in the memory array and couple the bit cells to other components used in read/write operations. 
         [0003]    For example, during a read operation, the voltage/current representing a state of a selected bit cell may be detected via the bit lines coupled to the selected bit cell. A sense amplifier may be coupled to the bit lines to amplify the differential voltage/current to aid in determining the logical state of the bit cell. 
         [0004]    As discussed above, a sense amplifier (SA) is a basic component that is used for operations in memory devices. A commonly used sense amplifier is a current latched sense amplifier (CLSA). 
         [0005]      FIG. 1  illustrates a conventional CLSA  100 . Referring to  FIG. 1 , the CLSA  100  includes NMOS transistors N 1  through N 5 , PMOS transistors P 1  through P 4  and capacitors C 1  and C 2 . The CLSA  100  receives differential input bit line BIT and inverted bit line BITB, sense signal SENSE and is coupled to a power supply voltage Vdd. 
         [0006]    Referring to  FIG. 1 , the differential inputs BIT, BITB are applied to gates of NMOS transistors N 1  and N 2 , respectively. The sense signal SENSE is applied to NMOS transistor N 5  and PMOS transistors P 1  and P 4 . When the sense signal SENSE is low, transistors P 1  and P 4  are conducting or “on” and allow capacitors C 1  and C 2  to charge. When the sense signal SENSE transitions to a higher logic level (e.g., “1”), the current through the gates N 1  and N 2  will be different if the voltages on differential inputs BIT and BITB are different. A different current flow through N 1 /N 3  and N 2 /N 4  will cause a voltage difference between output nodes sout and soutb as the capacitors will be discharged at a different rate. If a voltage on one of the output nodes (sout or soutb) reaches a threshold value to turn on one of cross coupled transistors P 2  or P 3 , and turn off one of corresponding transistors N 3  or N 4 , then a corresponding one of nodes sout or soutb will be coupled to Vdd. The other pair of transistors P 1 /N 3  or P 2 /N 4  cross coupled to the output node (sout or soutb) and coupled to Vdd will remain in a state with the PMOS transistor off and the NMOS transistor conducting. Accordingly, one of the output nodes sout or soutb will be latched to a high state and the other output node will be discharged, so the voltage differential between sout and soutb will be further amplified. 
         [0007]      FIG. 2  illustrates another conventional CLSA  200 . Referring to  FIG. 2 , the CLSA  200  includes NMOS transistors N 1  through N 5 , PMOS transistors P 1  through P 6  and capacitors C 1  and C 2 . The CLSA  200  receives differential inputs BIT and BITB, sense signal SENSE and is coupled to power supply voltage Vdd. The operation of the CLSA  200  is similar to that of the CLSA  100 . However, the CLSA  200  differs from CLSA  100  in that the differential inputs BIT and BITB are coupled to nodes sa and sab through PMOS transistors P 5  and P 6  (which are not present in CLSA  100 ) prior to a triggering of a sensing operation (when sense signal SENSE is low), which can increase a sensitivity of the CLSA  200  as compared to CLSA  100 . 
         [0008]    Thus, CLSA  100  and CLSA  200  are configured to sense voltage differentials in different manners. Also, CLSA  200  is able to achieve greater sensitivity than the CLSA  100  but only at the cost of including additional PMOS transistors, which can increase the layout area, power consumption and leakage of the sense amplifier. 
       SUMMARY 
       [0009]    Exemplary embodiments are directed to current latched sense amplifiers, related circuits and methods. 
         [0010]    Accordingly, an embodiment can include a current latched sense amplifier comprising: first and second transistors coupled to first and second bit lines, respectively, the first and second transistors configured to couple the first and second bit lines to first and second output nodes of the sense amplifier in a first phase and to isolate the first and second output nodes in a second phase; and third and fourth transistors having gates coupled to the first and second bit lines and coupled to current paths of the first second and first output nodes, respectively, and configured to be activated during the second phase. 
         [0011]    Another embodiment is directed to a method of sensing a differential between two bit lines, comprising: coupling a first bit line to a first output node of a sense amplifier and a second bit line to a second output node of the sense amplifier, in a first phase to supply an initial differential voltage to the sense amplifier; decoupling the first bit line from the first output node and the second bit line from the second output node during a second phase; and amplifying the initial differential voltage by discharging the first output node based on a voltage on the second bit line and the second output node based on a voltage on the first bit line, in the second phase. 
         [0012]    Another embodiment is directed to an apparatus for sensing a differential between two bit lines, comprising: means for coupling a first bit line to a first output node of a sense amplifier and a second bit line to a second output node of the sense amplifier, in a first phase to supply an initial differential voltage to the sense amplifier; means for decoupling the first bit line from the first output node and the second bit line from the second output node during a second phase; and means for amplifying the initial differential voltage by discharging the first output node based on a voltage on the second bit line and the second output node based on a voltage on the first bit line, in the second phase. 
         [0013]    Another embodiment is directed a method of sensing a differential between two bit lines, comprising: step for coupling a first bit line to a first output node of a sense amplifier and a second bit line to a second output node of the sense amplifier, in a first phase to supply an initial differential voltage to the sense amplifier; step for decoupling the first bit line from the first output node and the second bit line from the second output node during a second phase; and step for amplifying the initial differential voltage by discharging the first output node based on a voltage on the second bit line and the second output node based on a voltage on the first bit line, in the second phase. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    A more complete appreciation of embodiments and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings which are presented solely for illustration and not limitation of the embodiments. 
           [0015]      FIG. 1  illustrates a conventional current latched sense amplifier (CLSA). 
           [0016]      FIG. 2  illustrates another conventional current latched sense amplifier (CLSA). 
           [0017]      FIG. 3  illustrates a current latched sense amplifier (CLSA) according to at least one embodiment. 
           [0018]      FIG. 4  illustrates a flowchart for an exemplary method. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Aspects are disclosed in the following description and related drawings directed to specific embodiments. Alternate embodiments may be devised without departing from the scope of the invention. Additionally, well-known elements will not be described in detail or will be omitted so as not to obscure the relevant details of the disclosed embodiments. 
         [0020]    The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Likewise, the term “embodiments” does not require that all embodiments include the discussed feature, advantage or mode of operation. 
         [0021]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0022]    Further, many embodiments are described in terms of sequences of actions to be performed by, for example, elements of a computing device. It will be recognized that various actions described herein can be performed by specific circuits (e.g., application specific integrated circuits (ASICs)), by program instructions being executed by one or more processors, or by a combination of both. Additionally, these sequence of actions described herein can be considered to be embodied entirely within any form of computer readable storage medium having stored therein a corresponding set of computer instructions that upon execution would cause an associated processor to perform the functionality described herein. Thus, the various aspects of the embodiments may be embodied in a number of different forms, all of which have been contemplated to be within the scope of the claimed subject matter. In addition, for each of the embodiments described herein, the corresponding form of any such embodiments may be described herein as, for example, “logic configured to” perform the described action. 
         [0023]      FIG. 3  illustrates a dual sensing current latch sense amplifier (DSCLSA)  300  according to at least one embodiment. Referring to  FIG. 3 , the DSCLSA  300  includes NMOS transistors N 1  through N 5 , PMOS transistors P 1  through P 4  and capacitors C 1  and C 2 . The DSCLSA  300  receives differential bit line inputs BIT and BITB, sense signal SENSE and is coupled to supply voltage Vdd. As previously discussed, the bit lines may be couple to a plurality of bit cells in a memory array. A memory read operation can be coordinated with the DSCLSA  300  such that the sense signal SENSE can be triggered at an appropriate time after a bit cell has been selected to be read. The various control circuits for memory addressing, read and write operations are well known and will not be described herein. 
         [0024]    As illustrated in  FIG. 3 , any differential voltage between BIT/BITB is provided at sout and soutb at a drain terminal of cross coupled inverted amplifiers P 1 /N 3  and P 2 /N 4  (which can be considered a differential amplifier) and to gates of PMOS transistors P 1  and P 2 , respectively before the DSCLSA  300  is triggered. The differential voltage at sout and soutb is also provided at gates of NMOS transistors N 3  and N 4 . 
         [0025]    Referring to  FIG. 3 , the voltage differential of bit line BIT, BITB are also applied to the gates of NMOS transistors N 1  and N 2 , respectively, and are also applied to source inputs of PMOS transistors P 3  and P 4 , respectively. The sense signal SENSE is applied to the gates of NMOS transistor N 5  and PMOS transistors P 3  and P 4 . As will now be described in greater detail, the DSCLSA  300  is “dual sensing” because the DSCLSA  300  is capable of amplifying a voltage differential at sout and soutb in two different manners, which reinforce each other and increase a sensitivity of the DSCLSA  300 . 
         [0026]    It will be appreciated that in a first phase prior to triggering the DSCLSA  300 , when the sense signal SENSE is at a low logic level or logic “0”, a differential voltage may already be developed, at least partially, between the nodes sout and soutb. This is because PMOS transistors P 3  and P 4  are gated on when sense signal SENSE is set to the lower logic level, thereby coupling BIT to node sout and BITB to node soutb. 
         [0027]    In a second phase when the DSCLSA  300  is triggered, the sense signal SENSE transitions from the lower logic level to a higher logic level or “1”. PMOS transistors P 3  and P 4  transition to an “off” state, whereas NMOS transistor N 5  transitions to an “on” state. As noted above, the differential bit line inputs BIT, BITB are coupled to the gates of NMOS transistors N 1  and N 2 . Accordingly, when transistor N 5  turns on, the differential voltage applied to the gates of NMOS transistors N 1  and N 2  causes different currents at N 1  and N 2 , respectively. The different currents at NMOS transistors N 1  and N 2  increases the voltage differential at nodes sout and soutb by discharging capacitors C 1  and C 2  through transistors N 3  and N 4 , respectively. 
         [0028]    Accordingly, the voltage differential at sout and soutb that is amplified by the DSCLSA  300  is based on an initial differential voltage occurring prior to a transition of the sense signal SENSE from a lower logic level to a higher logic level which enhances the differential voltage determined when the sense signal SENSE transitions to the higher logic level. Also, the enhanced sensitivity of the DSCLSA  300  is provided without an increase in the number of components and without an increase in the area used in the layout of the DSCLSA  300 , over the conventional CLSA  100 . Additionally, fifth and sixth PMOS transistors P 5  and P 6 , which are present within the CLSA  200  of  FIG. 2 , need not be included within DSCLSA  300 . Accordingly, DSCLSA  300  may occupy less physical space, use less power, and have less leakage compared to CLSA  200  of  FIG. 2 . 
         [0029]    For example, referring to  FIG. 3 , assume that sense signal SENSE is set to the lower logic level, and a bit line voltage at BITB is equal to a bit line voltage at BIT. Next, assume during a memory operation the bit line voltage at BITB drops a given amount (e.g., 20 mV). The BIT and BITB bit line voltages pass through PMOS transistors P 4  and P 3 , respectively, until sense signal SENSE transitions to the higher logic level. Thus, sout and soutb are set to different voltages before sense signal SENSE transitions to the higher logic level. For example, this could be during a read operation prior to the DSCLSA  300  being triggered by sense signal SENSE and the output (sout, soutb) being read. Further, it will be appreciated that C 1  and C 2  do not have a discharge path through N 1 /N 3  and N 4 /N 2 , respectively, as transistor N 5  will be non-conducting or “off” prior to the transition of sense signal SENSE to the higher logic level. 
         [0030]    When signal SENSE transitions to the higher logic level to trigger the DSCLSA  300 , transistors P 3  and P 4  turn off, and transistor N 5  turns on, thereby providing a current path through transistor N 5  and discharge paths through transistors N 1 /N 3  and N 2 /N 4  for capacitors C 1  and C 2 , respectively. Additionally, the voltage differential which has already developed between sout and soutb is provided to the gates of N 1  and N 2 . This differential voltage at the gates of N 1  and N 2  causes different currents to flow through N 1  and N 2 , which reinforces the initial voltage difference at sout and soutb because the current through the gates N 1  and N 2  will be different if the voltages on differential inputs BIT and BITB are different. The different current flows through N 1 /N 3  and N 2 /N 4  will cause the voltage difference between output nodes sout and soutb to increase as the capacitors C 1  and C 2  will be discharged at different rates. 
         [0031]    For example in a first phase, assume that the difference between BIT and BITB is 20 mV prior to the DSCLSA  300  being triggered, as discussed above. This initial voltage differential will be provided to sout and soutb because transistors P 3  and P 4  are both on. Specifically, the voltage on BIT will be coupled to node sout via transistor P 4  and the voltage on BITB will be coupled to soutb via transistor P 3 . In the second phase, when the DSCLSA  300  is triggered (i.e., SENSE transitions to a high level), transistor N 5  is turned on and the current can flow through N 1  and N 2 . The current flowing through N 2  will be greater than that of N 1 , because of the higher voltage on BIT. This in turn will enhance the differential already established between soutb and sout, because the charge on C 2  coupled to node soutb will be discharged at a higher rate than C 1  coupled to node sout. 
         [0032]    Accordingly, the voltage differential at sout and soutb can be developed in response to a bit line voltage differential by two separate phases (i.e., both before and after SENSE transitions to a high level). This is accomplished without including additional transistors (e.g., as in  FIG. 2 ) which can increase the layout area of the sense amplifier. 
         [0033]    It will be appreciated that embodiments can include various methods for performing the processes, functions and/or algorithms disclosed herein. For example, as illustrated in  FIG. 4 , an embodiment can include a method of sensing a voltage differential at a sense amplifier. For example, the method can include coupling a first bit line (e.g., BIT) to a first output node (e.g., sout) and a second bit line (e.g., BITB) to a second output node (soutb), in a first phase to supply an initial differential voltage to the sense amplifier, block  402 . During a second phase, the first bit line is decoupled from the first output node and the second bit line is decoupled from the second output node, block  404 . Then, initial differential voltage (between sout and soutb) can be amplified by discharging the first output node (sout) based on a voltage on the second bit line (BITB) and the second output node (soutb) based on a voltage on the first bit line, in a second phase, block  406 . As discussed above, in the second phase transistors P 3  and P 4  decouple the bit lines from the output nodes/gars of the cross coupled inverters (P 1 /N 3  and P 2 /N 4 ), which leaves any differential voltage at the common output/gates. Also, during the second phase transistor N 5  is activated, which activates the sense amplifier in that current can flow through the inverters or at least though N 3 /N 4  to discharge the output nodes if P 1  or P 2  is gated off Essentially, the voltage differential will be amplified, because the lower voltage (of the initial differential voltage) will be applied to the gate of the transistor (N 1 /N 2 ) coupled in series with the higher voltage node (sout/soutb) and higher voltage will be applied to the gate of the transistor (N 1 /N 2 ) coupled in series with the lower voltage node (sout/soutb). Accordingly, the reverse differential is applied to gates of the transistors in the current path of the output nodes. 
         [0034]    It will be appreciated that the method illustrated in the flowchart of  FIG. 4  is merely one embodiment and is not intended to limit the various embodiments to the illustrated examples. For example, other functional aspects/sequence of actions discussed herein may be added to the actions discussed in relation to  FIG. 4  including alternatives to the actions already described. 
         [0035]    Those of skill in the art will appreciate that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
         [0036]    Further, it will be appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the invention. 
         [0037]    In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM, a solid state memory device, such as a flash-drive, or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
         [0038]    It will be appreciated that sense amplifiers, as illustrated for example in  FIG. 3 , may be included within a mobile phone, portable computer, hand-held personal communication system (PCS) unit, portable data units such as personal data assistants (PDAs), GPS enabled devices, navigation devices, settop boxes, music players, video players, entertainment units, fixed location data units such as meter reading equipment, or any other device that stores or retrieves data or computer instructions, or any combination thereof. Accordingly, embodiments may include any device which includes sense amplifiers as disclosed herein. 
         [0039]    Further, it will be appreciated that various to memory devices can include an multiple sense amplifiers as disclosed herein. Accordingly, although potions of the foregoing disclosure discuss the sense amplifier in isolation, it will be appreciated that various embodiments can include devices into which the sense amplifier is integrated, such as memory devices comprising arrays of memory cells and a plurality of sense amplifiers. 
         [0040]    The foregoing disclosed devices and methods may be designed and configured into GDSII and GERBER computer files, stored on a computer readable media. These files are in turn provided to fabrication handlers who fabricate devices based on these files. The resulting products are semiconductor wafers that are then cut into semiconductor die and packaged into a semiconductor chip. The chips are then employed in devices described above. 
         [0041]    Accordingly, embodiments can include machine-readable media or computer-readable media embodying instructions which when executed by a processor transform the processor and any other cooperating elements into a machine for performing the functionalities described herein as provided for by the instructions. Accordingly, the scope of the invention is not limited to illustrated examples and any means for performing the functionality described herein are included in embodiments. 
         [0042]    While the foregoing disclosure shows illustrative embodiments, it should be noted that various changes and modifications could be made herein without departing from the scope of the invention as defined by the appended claims. The functions, steps and/or actions of the method claims in accordance with the embodiments described herein need not be performed in any particular order. Furthermore, although elements of embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.