Apparatuses and methods for performing compare operations using sensing circuitry

The present disclosure includes apparatuses and methods related to performing compare and/or report operations using sensing circuitry. An example method can include charging an input/output (IO) line of a memory array to a voltage. The method can include determining whether data stored in the memory array matches a compare value. The determination of whether data stored matches a compare value can include activating a number of access lines of the memory array. The determination can include sensing a number of memory cells coupled to the number of access lines. The determination can include sensing whether the voltage of the IO line changes in response to activation of selected decode lines corresponding to the number of memory cells.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor memory and methods, and more particularly, to apparatuses and methods related to performing compare operations using sensing circuitry.

BACKGROUND

Electronic systems often include a number of processing resources (e.g., one or more processors), which may retrieve and execute instructions and store the results of the executed instructions to a suitable location. A processor can comprise a number of functional units such as arithmetic logic unit (ALU) circuitry, floating point unit (FPU) circuitry, and/or a combinatorial logic block, for example, which can be used to execute instructions by performing logical operations such as AND, OR, NOT, NAND, NOR, and XOR logical operations on data (e.g., one or more operands). For example, the functional unit circuitry (FUC) may be used to perform arithmetic operations such as addition, subtraction, multiplication, and/or division on operands.

A number of components in an electronic system may be involved in providing instructions to the FUC for execution. The instructions may be generated, for instance, by a processing resource such as a controller and/or host processor. Data (e.g., the operands on which the instructions will be executed) may be stored in a memory array that is accessible by the FUC. The instructions and/or data may be retrieved from the memory array and sequenced and/or buffered before the FUC begins to execute instructions on the data. Furthermore, as different types of operations may be executed in one or multiple clock cycles through the FUC, intermediate results of the instructions and/or data may also be sequenced and/or buffered.

Executing instructions (e.g, as part of program execution) can involve performing operations such as compare operations and the results can be provided (e.g., reported) to the processing resources as part of the executional flow of an algorithm, for example. Such compare and report functionality can enable, for instance, “if-then-else” programmatic flow, which is often part of program execution.

DETAILED DESCRIPTION

The present disclosure includes apparatuses and methods related to performing compare operations using sensing circuitry. An example method comprises charging (e.g., precharging) an input/output (IO) line (e.g., a local IO line (LIO line)) of a memory array to a pvoltage (e.g., a precharge voltage). The method can include determining whether data stored in the memory array matches a compare value by activating a number of access lines of the memory array and sensing a number of memory cells coupled to the number of access lines. The method can include sensing whether the voltage (e.g., precharge voltage) of the LIO line changes in response to activation of selected decode lines (e.g., column decode lines) corresponding to the number of memory cells. In the present disclosure, a “line” is meant to refer to an operable coupling between at least two nodes.

A number of embodiments of the present disclosure can provide benefits such as improved compare and report functionality in association with determining whether a match exists between a compare value (e.g., a particular data value and/or set of data values) and a data value stored in a memory array. For instance, a number of embodiments can provide for identifying whether particular data is stored in a number of memory cells without transferring data out of the memory array and sensing circuitry via a bus (e.g., data bus, address bus, control bus), for instance. The determination of whether data stored in the array matches the compare value can be reported, for instance, to control circuitry (e.g., to an on-die controller and/or to an external host). The determination of whether data stored in the array matches the compare value can be reported into the memory array. Such compare and report functionality can be associated with performing a number of logical operations (e.g., AND, NOT, NOR, NAND, XOR, etc.). However, embodiments are not limited to these examples.

Also, circuitry such as FUC associated with various processing resource(s) may not conform to pitch rules associated with a memory array. For example, the cells of a memory array may have a 4F2or 6F2cell size, where “F” is a feature size corresponding to the cells. The devices (e.g., logic gates) associated with FUC of previous systems may not be capable of being formed on pitch with the memory cells, which can affect chip size and/or memory density, for example.

FIG. 1is a block diagram of an apparatus in the form of a computing system100including a memory device120in accordance with a number of embodiments of the present disclosure. As used herein, a memory device120, a memory array130, and/or sensing circuitry150might also be separately considered an “apparatus.”

System100includes a host110coupled to memory device120, which includes a memory array130. Host110can be a host system such as a personal laptop computer, a desktop computer, a digital camera, a mobile telephone, or a memory card reader, among various other types of hosts. Host110can include a system motherboard and/or backplane and can include a number of processing resources (e.g., one or more processors, microprocessors, or some other type of controlling circuitry). The system100can include separate integrated circuits or both the host110and the memory device120can be on the same integrated circuit. The system100can be, for instance, a server system and/or a high performance computing (HPC) system and/or a portion thereof. Although the example shown inFIG. 1illustrates a system having a Von Neumann architecture, embodiments of the present disclosure can be implemented in non-Von Neumann architectures (e.g., a Turing machine), which may not include one or more components (e.g., CPU, ALU, etc.) often associated with a Von Neumann architecture.

For clarity, the system100has been simplified to focus on features with particular relevance to the present disclosure. The memory array130can be a DRAM array, SRAM array, STT RAM array, PCRAM array, TRAM array, RRAM array, NAND flash array, and/or NOR flash array, for instance. The array130can comprise memory cells arranged in rows coupled by access lines (which may be referred to herein as row lines, word lines or select lines) and columns coupled by sense lines (which may be referred to herein as digit lines or data lines). Although a single array130is shown inFIG. 1, embodiments are not so limited. For instance, memory device120may include a number of arrays130(e.g., a number of banks of DRAM cells). An example DRAM array is described in association withFIGS. 2 and 3.

The memory device120includes address circuitry142to latch address signals provided over an I/O bus156(e.g., a data bus) through I/O circuitry144. Address signals are received and decoded by a row decoder146and a column decoder152to access the memory array130. Data can be read from memory array130by sensing voltage and/or current changes on the sense lines using sensing circuitry150. The sensing circuitry150can read and latch a page (e.g., row) of data from the memory array130. The I/O circuitry144can be used for bi-directional data communication with host110over the I/O bus156. The write circuitry148is used to write data to the memory array130.

Control circuitry140decodes signals provided by control bus154from the host110. These signals can include chip enable signals, write enable signals, and address latch signals that are used to control operations performed on the memory array130, including data read, data write, and data erase operations. In various embodiments, the control circuitry140is responsible for executing instructions from the host110. The control circuitry140can be a state machine, a sequencer, or some other type of controller (e.g., an on-die controller).

An example of the sensing circuitry150is described further below in association withFIGS. 2 and 3. For instance, in a number of embodiments, the sensing circuitry150can comprise a number of sense amplifiers (e.g., sense amplifiers206-1, . . . ,206-P shown inFIG. 2or sense amplifier306shown inFIG. 3) and a number of compute components (e.g., compute component331shown inFIG. 3), which may comprise an accumulator and can be used to perform compare and report operations (e.g., on data associated with complementary sense lines). In a number of embodiments, the sensing circuitry (e.g.,150) can be used to perform compare and report operations using data stored in array130as inputs and store the results of the logical operations back to the array130without transferring via a sense line address access (e.g., without firing a column decode signal). As such, various compute functions can be performed within array130using sensing circuitry150rather than being performed by processing resources external to the sensing circuitry (e.g., by a processor associated with host110and/or other processing circuitry, such as ALU circuitry, located on device120(e.g., on control circuitry140or elsewhere)). In various previous approaches, data associated with an operand, for instance, would be read from memory via sensing circuitry and provided to external ALU circuitry via local I/O lines. The external ALU circuitry would perform compute functions using the operands and the result would be transferred back to the array via the local I/O lines. In contrast, in a number of embodiments of the present disclosure, sensing circuitry (e.g.,150) can be configured to perform logical operations on data stored in memory (e.g., array130) and store the result to the memory without enabling a local I/O line coupled to the sensing circuitry.

FIG. 2illustrates a schematic diagram of a portion of a memory array coupled to sensing circuitry in accordance with a number of embodiments of the present disclosure. In this example, the memory array is a DRAM array of memory cells (MCs)260-1, . . . ,260-N. In a number of embodiments, the memory cells are destructive read memory cells (e.g., reading the data stored in the cell destroys the data such that the data originally stored in the cell is refreshed after being read). The memory cells260-1, . . . ,260-N of the array inFIG. 2can be arranged in a number of rows coupled by word line204and columns coupled by sense lines (e.g., digit lines)205-1, . . . ,205-M. For ease of reference, the sense lines205-1, . . . ,205-M represent respective pairs of complementary sense lines (e.g.,305-1and305-2inFIG. 3). Although only one row and two columns of memory cells are illustrated inFIG. 2, embodiments are not so limited. For instance, a particular array may have a number of columns of memory cells and/or sense lines (e.g., 4,096, 8,192, 16,384, etc.). As an example, a gate of a particular memory cell transistor (e.g.,302inFIG. 3) can be coupled to its corresponding word line (204), a source/drain region can be coupled to its corresponding sense line (e.g.,205-1), and a second source/drain region of a particular memory cell transistor can be coupled to its corresponding capacitor (e.g.,303inFIG. 3).

The array inFIG. 2can be coupled to sensing circuitry in accordance with a number of embodiments of the present disclosure. In this example, the sensing circuitry comprises sense amplifiers206-1,206-P and secondary sense amplifier (SSA)268. The sensing circuitry can be sensing circuitry150shown inFIG. 1. The sense amplifiers206-1to206-P are coupled to the respective sense lines205-1to205-M. The sense amplifiers206-1to206-P can be sense amplifiers such as sense amplifier306described below in association withFIG. 3. The sense amplifiers206-1to206-P are coupled to input/output lines266-1(IO) and266-2(IO_) via transistors218-1and218-2, respectively. Column decode lines264-1(CD-1) to264-R (CD-R) are coupled to the gates of transistors218-1and218-2and can be selectively activated to transfer data sensed by respective sense amps206-1to206-P to the SSA268via IO lines266-1and266-2

In operation, sense amps (e.g.,206-1to206-P) can sense a data value (e.g., a logic “1” or “0”) stored in a memory cell (e.g.,260-1to260-N) by amplifying a differential signal (e.g., voltage or current) on the complementary sense lines (e.g.,205-1to205-M) responsive to activation of a selected row line (e.g.,204). As an example, the sense amps206-1to206-P can drive one of the sense lines (e.g., D) of the pair of complementary sense lines205-1to a first value (e.g., to a supply voltage such as Vcc), and the other sense line (D_) of the pair of complementary sense lines205-1to a second value (e.g., to a reference voltage such as a ground voltage). In this manner, the data value stored by the memory cell (e.g.,260-1) can be determined based on which of the sense lines of the complementary sense line pair is driven to Vcc, for instance. The voltages of the complementary sense line pairs205-1to205-M can then be selectively transferred to the IO lines266-1and266-2via activation of the column decode lines264-1to264-R. In this manner, the data sensed by the sense amps206-1to206-P can be transferred to the SSA268via IO lines266-1and266-2. Often, the SSA268may only be capable of storing a data value from a single cell (e.g., one of cells260-1to260-N) at a particular time. As such, if it is desired to transfer the data stored in cell260-1to the SSA268, then column decode line264-1would be activated, and if it is desired to transfer the data stored in cell260-N to the SSA268, then column decode264-R would be activated. If both lines264-1and264-R were activated, the SSA268may not be able to determine the actual stored data values stored in either of the cells.

However, in various instances, it can be useful to selectively activate more than one of the column decode lines (e.g.,264-1to264-R). For example, selectively activating a number of column decode lines can be done in association with performing a compare operation in accordance with a number of embodiments described herein. For instance, in a number of embodiments of the present disclosure, the data path portion shown inFIG. 2can be operated to determine whether data stored in a memory array (e.g., array130) matches a compare value, which may be provided by an on-die control circuit (e.g., control circuitry140) and/or by external control circuitry (e.g., host110) as part of an “if-then-else” programmatic flow, for example.

In a number of embodiments, control circuitry (e.g.,140inFIG. 1) can be configured to charge (e.g., precharge) an IO line (e.g.,266-1) to a voltage (e.g., a precharge voltage). For example, the IO line266-1can be precharged to a voltage (e.g., a supply voltage such as Vcc) corresponding to a logic “1.” The control circuitry can be configured to selectively activate row lines (e.g., a row line including memory cells260-1, . . . ,260-N) and column decode lines (e.g., CD-1, . . . , CD-R). Sensing circuitry (e.g.,150inFIG. 1) can be configured to sense a number of selected memory cells (e.g.,260-1, . . . ,260-N) coupled to an activated row line. The sensing circuitry can be configured to determine whether the precharge voltage of the IO line266-1changes in response to selective activation of column decode lines CD-1 to CD-R.

In a number of embodiments, the control circuitry (e.g.,140inFIG. 1) can, in conjunction with the sensing circuitry, can be used to perform a compare function (e.g., to determine if data stored in the memory array matches a compare value). As an example, the IO line266-1can be precharged to a particular voltage. The particular voltage can be a voltage corresponding to a data value. For instance the precharge voltage can be a supply voltage such as Vcc, which may correspond to a logic “1,” or a ground voltage, which may correspond to a logic “0.”

Activation of column decode line CD-1 turns on transistors218-1and218-2, which provides voltages corresponding to the data stored in sense amp206-1to IO lines266-1and266-2. As such, the precharge voltage of IO line266-1can change based on the particular data value stored in sense amp206-1(which represents the data stored in a particular memory cell such as cell260-1). For example, if the sense amplifier206-1senses a logic 0 (e.g., a ground voltage) stored in cell260-1, then the precharge voltage (e.g., Vcc) on the IO line266-1will be pulled down (e.g., lowered) when CD-1 is activated, and the change in the precharge voltage change can be detected by the SSA268. As such, the detected change in the precharge voltage indicates that the sensed memory cell (e.g.,260-1) stores a data value (e.g., 0) different from the data value (e.g., 1) corresponding to the precharge voltage. Similarly, if the sense amplifier206-1senses a logic 1 (e.g., Vcc) stored in cell260-1, then the precharge voltage (e.g., Vcc) on the IO line266-1will not be pulled down when CD-1 is activated, and no change in the precharge voltage will be detected by the SSA268. As such, no detected change in the precharge voltage indicates that the sensed memory cell (e.g.,260-1) stores the same data value (e.g., 1) as the data value (e.g., 1) corresponding to the precharge voltage.

The above described ability of the SSA268to determine whether the precharge voltage changes can be used to perform compare functions to determine whether a particular compare value matches data stored in a memory array, for instance. As an example, if an operation requires knowledge of whether a number of cells coupled to a particular row line stores a particular compare value (e.g., 0), the particular row line can be activated along with the sense lines corresponding the number of memory cells. If any of the cells store a 0, then the precharge voltage of the IO line (e.g., local IO line) will be changed (e.g., pulled down). The result of the operation can be reported, for instance, to the requesting control circuitry (e.g., on-die controller, host, etc.). The result of the operation can be reported into the memory array for further calculations. The determined result may be used as part of continued execution of a particular algorithm. For instance, execution may include not only determining if any of the memory cells of the row store a data value (e.g., 0), but which cell(s) store the data value. As such, subsets of the column decode lines may be selectively activated to compare the data values stored by their corresponding cells to the compare value, which can be used in association with binary searching, for instance.

The compare values used in association with compare operations can be requested by control circuitry coupled to the sense circuitry (e.g., on-die controller) and/or by a number of other sources such as an external host, for instance. Similarly, results of compare operations can be reported to various control circuitry and/or used to perform further operations (e.g., logic operations) as part of if-then-else programmatic flow prior to being reported to control circuitry.

FIG. 3illustrates a schematic diagram of a portion of a memory array330coupled to sensing circuitry in accordance with a number of embodiments of the present disclosure. In this example, the memory array330is a DRAM array of 1T1C (one transistor one capacitor) memory cells each comprised of an access device302(e.g., transistor) and a storage element303(e.g., a capacitor). In a number of embodiments, the memory cells are destructive read memory cells (e.g., reading the data stored in the cell destroys the data such that the data originally stored in the cell is refreshed after being read). The cells of array330are arranged in rows coupled by word lines304-0(Row0),304-1(Row1),304-2, (Row2)304-3(Row3), . . . ,304-N (RowN) and columns coupled by sense lines (e.g., digit lines)305-1(D) and305-2(D_). In this example, each column of cells is associated with a pair of complementary sense lines305-1(D) and305-2(D_). Although only a single column of memory cells is illustrated inFIG. 3, embodiments are not so limited. For instance, a particular array may have a number of columns of memory cells and/or sense lines (e.g., 4,096, 8,192, 16,384, etc.). A gate of a particular memory cell transistor302is coupled to its corresponding word line304-0,304-1,304-2,304-3, . . . ,304-N, a first source/drain region is coupled to its corresponding sense line305-1, and a second source/drain region of a particular memory cell transistor is coupled to its corresponding capacitor303. Although not illustrated inFIG. 3, the sense line305-2may also be coupled to a column of memory cells.

The array330is coupled to sensing circuitry in accordance with a number of embodiments of the present disclosure. In this example, the sensing circuitry comprises a sense amplifier306and a compute component331. The sensing circuitry can be sensing circuitry150shown inFIG. 1. The sense amplifier306is coupled to the complementary sense lines D, D_corresponding to a particular column of memory cells. The sense amp306can be operated to determine a state (e.g., logic data value) stored in a selected cell. Embodiments are not limited to the example sense amplifier306. For instance, sensing circuitry in accordance with a number of embodiments described herein can include current-mode sense amplifiers and/or single-ended sense amplifiers (e.g., sense amplifiers coupled to one sense line).

In a number of embodiments, a compute component (e.g.,331) can comprise a number of transistors formed on pitch with the transistors of the sense amp (e.g.,306) and/or the memory cells of the array (e.g.,330), which may conform to a particular feature size (e.g., 4F2, 6F2, etc.). As described further below, the compute component331can, in conjunction with the sense amp306, operate to perform various compare and report operations using data from array330as input and store the result back to the array330without transferring the data via a sense line address access (e.g., without firing a column decode signal such that data is transferred to circuitry external from the array and sensing circuitry via local I/O lines (e.g.,266-1inFIG. 2).

In the example illustrated inFIG. 3, the circuitry corresponding to compute component331comprises five transistors coupled to each of the sense lines D and D_; however, embodiments are not limited to this example. Transistors307-1and307-2have a first source/drain region coupled to sense lines D and D_, respectively, and a second source/drain region coupled to a cross coupled latch (e.g., coupled to gates of a pair of cross coupled transistors, such as cross coupled NMOS transistors308-1and308-2and cross coupled PMOS transistors309-1and309-2. As described further herein, the cross coupled latch comprising transistors308-1,308-2,309-1, and309-2can be referred to as a secondary latch (the cross coupled latch corresponding to sense amp306can be referred to herein as a primary latch).

The transistors307-1and307-2can be referred to as pass transistors, which can be enabled via respective signals311-1(Passd) and311-2(Passdb) in order to pass the voltages or currents on the respective sense lines D and D_to the inputs of the cross coupled latch comprising transistors308-1,308-2,309-1, and309-2(e.g., the input of the secondary latch). In this example, the second source/drain region of transistor307-1is coupled to a first source/drain region of transistors308-1and309-1as well as to the gates of transistors308-2and309-2. Similarly, the second source/drain region of transistor307-2is coupled to a first source/drain region of transistors308-2and309-2as well as to the gates of transistors308-1and309-1.

A second source/drain region of transistor308-1and308-2is commonly coupled to a negative control signal312-1(Accumb). A second source/drain region of transistors309-1and309-2is commonly coupled to a positive control signal312-2(Accum). The Accum signal312-2can be a supply voltage (e.g., Vcc) and the Accumb signal can be a reference voltage (e.g., ground). Enabling signals312-1and312-2activates the cross coupled latch comprising transistors308-1,308-2,309-1, and309-2corresponding to the secondary latch. The activated sense amp pair operates to amplify a differential voltage between common node317-1and common node317-2such that node317-1is driven to one of the Accum signal voltage and the Accumb signal voltage (e.g., to one of Vcc and ground), and node317-2is driven to the other of the Accum signal voltage and the Accumb signal voltage. As described further below, the signals312-1and312-2are labeled “Accum” and “Accumb” because the secondary latch can serve as an accumulator while being used to perform a logical operation. In a number of embodiments, an accumulator comprises the cross coupled transistors308-1,308-2,309-1, and309-2forming the secondary latch as well as the pass transistors307-1and308-2. As described further herein, in a number of embodiments, a compute component comprising an accumulator coupled to a sense amplifier can be configured to perform a logical operation that comprises performing an accumulate operation on a data value represented by a signal (e.g., voltage or current) on at least one of a pair of complementary sense lines.

The compute component331also includes inverting transistors314-1and314-2having a first source/drain region coupled to the respective digit lines D and D_. A second source/drain region of the transistors314-1and314-2is coupled to a first source/drain region of transistors316-1and316-2, respectively. The gates of transistors314-1and314-2are coupled to a signal313(InvD). The gate of transistor316-1is coupled to the common node317-1to which the gate of transistor308-2, the gate of transistor309-2, and the first source/drain region of transistor308-1are also coupled. In a complementary fashion, the gate of transistor316-2is coupled to the common node317-2to which the gate of transistor308-1, the gate of transistor309-1, and the first source/drain region of transistor308-2are also coupled. As such, enabling signal InvD serves to invert the data value stored in the secondary latch and drives the inverted value onto sense lines305-1and305-2.

In a number of embodiments of the present disclosure, a compare operation can include activating a row of memory cells (e.g., row line204) to determine if there is a match in the row line (e.g., at least one memory cell stores a compare value). A compare operation can be expanded to include comparing a 32-bit compare value to data stored in the array. For example, compare values of a number of memory cells can be aggregated in an accumulator (as described above) to determine if there is a collection of compare values that match a 32-bit compare value.

Embodiments of the present disclosure are not limited to the particular sensing circuitry configuration illustrated inFIGS. 2 and 3. For instance, different compute component circuitry can be used to perform logical operations in accordance with a number of embodiments described herein.

FIG. 4illustrates an example of a method for performing a compare operation in accordance with a number of embodiments of the present disclosure. At block470, the method includes precharging an input/output (IO) line (e.g.,266-1inFIG. 2) of a memory array (e.g.,330inFIG. 3) to a precharge voltage. The IO line (e.g., a local IO line) can be precharged, for instance, to a voltage corresponding to a particular data value, such as a supply voltage (e.g., Vcc corresponding to logic 1) or a reference voltage (e.g., a ground voltage corresponding to logic 0). A number of embodiments can include precharging a LIO_line (e.g.,266-2inFIG. 2) of a memory array to a precharge voltage. The voltage to which the LIO_line is precharged can be an inverse of a voltage to which the LIO line is precharged.

At block472, the method includes determining whether data stored in the memory array matches a compare value. The compare value can be a value provided by an external host (e.g., an external processor) and/or an on die controller. The compare value can include a number of different data values that the control circuitry is attempting to determine whether are stored in at least one memory cell in a memory array. The compare value can be stored in a number of memory cells. For example, the data can be stored in one, two, three, etc., memory cells. A match can refer to a determination that a compare value provided by the control circuitry is stored in at least one memory cell of the array. A determination that the compare value is not stored in at least one memory cell can indicate that there is not a match.

The determination of whether data stored in the memory array matches a compare value can be determined, at block474, by activating a number of row lines of the memory array. The number of row lines can be selectively activated based on a characteristic of the row lines. The number of row lines can include particular row lines that are predetermined by a controller (e.g., an external host, an on-die controller).

The determination of whether data stored in the memory array matches a compare value can be determined, at block476, by sensing a number of memory cells coupled to the number of row lines. The voltage of the memory cells of the row lines of the memory array can be sensed by the sense amplifiers and column decode lines can be activated to provide the voltage of the sense amplifers (and corresponding memory cells) to the LIO line.

The determination of whether data stored in the memory array matches a compare value can be determined, at block478, by sensing whether the precharge voltage of the LIO line changes in response to activation of selected column decode lines corresponding to the number of memory cells. For example, the LIO line can be precharged to a supply voltage (e.g., Vcc) corresponding to a logic 1. A memory cell in the memory array may store a data value (e.g., logic 0) corresponding to a compare value that a controller is trying to locate (e.g., match). When the memory cell is activated and the voltage of the cell is provided to the LIO line (e.g., via the corresponding sense amp), the voltage on the LIO line (e.g., precharge voltage) will drop if the data value stored by the cell matches the compare value (e.g., if the data value stored by the cell is a logic 0). The secondary sense amplifier can detect the drop in voltage and determine that a match has occurred. The determination of the match can be reported to circuitry that provided the compare value (e.g., an on die controller, an external host, etc.) and/or to some other control circuitry for further use. If a match is determined, further operations can be performed to determine a particular location (e.g., cell or cells) within the array where the match occurs. Peripheral control logic can read a data path to determine the compare state of the memory array. Locating the match can include a search method (e.g., a binary search) to determine which memory cell in the memory array matched. The match can occur at a number of memory cells (e.g, no memory cell, one memory cell, or a plurality of memory cells).