TWI844013B - Content addressable memory device, content addressable memory cell and method for data searching and comparing thereof - Google Patents

Abstract

The application provides a content addressable memory (CAM) memory device, a CAM memory cell and a method for searching and comparing data thereof. The CAM memory device includes: a plurality of CAM memory strings; and an electrical characteristic detection circuit. In data searching, a search data is compared with a storage data stored in the CAM memory strings, the CAM memory strings generate a plurality of memory string currents, the electrical characteristic detection circuit detects the memory string currents to generate a plurality of sensing results, or detects a plurality of match line voltages on a plurality of match lines coupled to the CAM memory string to generate the plurality of search results. The storage data and the search data is a range storage data and a single-bit search data, or the storage data and the search data is a single-bit storage data and a range search data.

Description

Content-addressable memory device, content-addressable memory cell and its data search and comparison method

The present invention relates to a content addressable memory (CAM), a CAM cell device and a data search and comparison method thereof, and in particular to a CAM device, a CAM cell and a data search and comparison method thereof that can be used to implement in-memory approximate searching.

With the rise of big data and artificial intelligence (AI) hardware accelerators, data search and data comparison are important functions. Existing ternary content addressable memory (TCAM) can be used to achieve highly parallel searching. Traditional TCAM is usually composed of static random access memory (SRAM), so the memory density is low and the access power is high. In order to improve the memory density and save power consumption, a non-volatile memory array based on TCAM has been proposed recently.

Compared to SRAM-based TCAMs with 16 transistors (16T), RRAM-based TCAMs with 2 transistors and 2 resistors (2T2R) have been recently developed to reduce the cell area. Standby power consumption can also be improved by using RRAM-based non-volatile TCAMs. However, existing non-volatile TCAMs have difficulty implementing range search and range storage, as well as in-memory approximate searching.

Therefore, there is a need for a content addressable memory (CAM) device, a CAM memory cell, and a data search and comparison method thereof, which can be used to implement similarity search within the memory, and to implement range search and range storage.

According to an example of the present invention, a content-addressable memory device is provided, comprising: a plurality of content-addressable memory strings; and an electrical characteristic detection circuit coupled to the content-addressable memory strings; wherein, when performing a data search, a search data is compared with a storage data stored in the content-addressable memory strings, and the content-addressable memory strings generate a plurality of memory string currents. The electrical characteristic detection circuit detects the memory string currents or detects the plurality of match line voltages of the plurality of match lines coupled to the content-addressed memory strings to generate a plurality of search results, wherein the storage data and the search data are a range storage data and a single-bit search data, or the storage data and the search data are a single-bit storage data and a range search data.

According to another example of the present case, a data search and comparison method of a content-addressable memory device is proposed, including: storing a storage data in a plurality of content-addressable memory strings; performing a data search on the content-addressable memory strings with a search data; the content-addressable memory strings generate a plurality of memory string currents; detecting the memory string currents or detecting a plurality of match line voltages of a plurality of match lines coupled to the content-addressable memory strings to generate a plurality of search results, wherein the storage data and the search data are a range storage data and a single-bit search data, or the storage data and the search data are a single-bit storage data and a range search data.

According to another embodiment of the present invention, a content-addressable memory cell is provided, comprising: a plurality of memory cells, wherein the memory cells are connected in series, and a plurality of search voltages representing a search data are input to a plurality of control terminals of the memory cells; or the control terminals of the memory cells receive a selection voltage or a pass voltage, and the search voltages are input to a plurality of first terminals of the memory cells through a plurality of signal lines; or the memory cells The control terminals of the cells are coupled to a plurality of word lines to receive the search voltages, and the first terminals of the memory cells are further coupled to a matching line and a precharge control circuit, and the second terminals of the memory cells are coupled to a ground terminal, wherein a storage data and the search data of the content-addressable memory cell are a range storage data and a single-bit search data, or the storage data and the search data are a single-bit storage data and a range search data.

In order to better understand the above and other aspects of the present invention, the following is a specific example and a detailed description with the attached drawings as follows:

200, 300, 400, 500: content-addressable memory cells

T1~T4: Flash memory cell

WL1~WL4, WL21~WL28, WL31~WL38, WL41~WL44: character lines

SS21~SS24, SS31~SS34: memory string

C21~C28, C31~C38: content-addressable memory cells

SA: Inductive amplifier

BL1~BL12: bit line

ML, ML1~MLn: matching line

501: Pre-charge control circuit

502: Voltage detection circuit

710~740: Steps

Figure 1A shows a schematic diagram of single-bit storage data and single-bit search data.

Figure 1B shows a schematic diagram of range storage data and single-bit search data.

Figure 1C shows a schematic diagram of single-bit storage data and range search data.

FIG. 2A shows a content-addressable memory cell according to the second embodiment of the present invention, and its critical voltage distribution diagram.

Figure 2B shows a schematic diagram of the "range storage and single bit search" operation according to the second embodiment of the present invention.

FIG. 3A shows a content-addressable memory cell according to the third embodiment of the present invention, and its critical voltage distribution diagram.

Figure 3B shows a schematic diagram of the "range storage and single bit search" operation according to the third embodiment of the present invention.

FIG. 4A shows a content-addressable memory cell according to the fourth embodiment of the present invention, and its critical voltage distribution diagram.

Figures 4B and 4C show schematic diagrams of the "range storage and single bit search" operation according to the fourth embodiment of the present invention.

FIG. 5A shows a content-addressable memory cell according to the fifth embodiment of the present invention, and its critical voltage distribution diagram.

Figure 5B shows a schematic diagram of the "range storage and single bit search" operation according to the fifth embodiment of the present invention.

Figures 6A and 6B show the operation diagrams of "range storage and single bit search" and "single bit storage and range search" according to an embodiment of the present invention.

Figure 7 shows a flow chart of a data search and comparison method of a CAM memory device according to an embodiment of the present invention.

The technical terms in this specification refer to the customary terms in this technical field. If this specification explains or defines some terms, the interpretation of these terms shall be based on the explanation or definition in this specification. Each embodiment disclosed in this disclosure has one or more technical features. Under the premise of possible implementation, a person with ordinary knowledge in this technical field can selectively implement part or all of the technical features in any embodiment, or selectively combine part or all of the technical features in these embodiments.

In one embodiment of the present invention, a CAM memory device, a CAM memory cell and a data search and comparison method thereof that can implement memory proximity search are disclosed. Search data is input to a content-addressable memory cell via a word line or a bit line, and storage data is stored in the content-addressable memory cell. In one embodiment of the present invention, the storage data stored in the content-addressable memory cell can be range storage data (i.e., the stored data is range data), and the search data is single-bit search data. Alternatively, in another embodiment of the present case, the storage data stored in the content-addressable memory cell may be single-bit storage data (that is, the stored data is single-bit data), and the search data is range search data. The definitions of "range storage data" and "range search data" will be explained below.

In one embodiment of the present invention, when performing data search or data comparison, in a matching state, the content addressable memory cell provides a cell current; and, in a mismatching state, the content addressable memory cell does not provide a cell current. In another embodiment of the present invention, when performing data search or data comparison, in a matching state, the content addressable memory cell does not provide a cell current; and, in a mismatching state, the content addressable memory cell provides a cell current.

In one embodiment of the present invention, when the search data fully matches the stored data, a memory string provides a high memory string current; when the search data partially matches the stored data, the memory string provides a medium memory string current; and, when the search data does not match the stored data at all, the memory string provides a low memory string current. In another embodiment of the present invention, when the search data fully matches the stored data, a memory string provides a low memory string current; when the search data partially matches the stored data, the memory string provides a medium memory string current; and, when the search data does not match the stored data at all, the memory string provides a high memory string current. That is, the size of the memory string current depends on the degree of match (or mismatch) between the search data and the stored data.

In addition, in another embodiment of the present case, when the search data fully matches the stored data, the match line voltage on the match line can be maintained without being discharged (i.e., no discharge current); when the search data partially matches the stored data, the match line voltage on the match line will be moderately discharged (i.e., the discharge current is a moderate discharge current); and, when the search data does not match the stored data at all, the match line voltage on the match line will be highly discharged (i.e., the discharge current is a high discharge current). That is, the discharge degree of the match line voltage depends on the degree of match (or mismatch) between the search data and the stored data.

Figure 1A shows a schematic diagram of single-bit storage data and single-bit search data. Take the CAM cell as an example. The single-bit storage data of a single CAM cell can be logic 1, logic 0, or X (don’t care). The single-bit search data can be logic 1, logic 0, or wildcard (WC). When the search data matches the storage data, the search result is a match, and vice versa.

FIG. 1B is a schematic diagram showing range storage data and single-bit search data. The range storage data of a single content-addressable memory cell can be range data or X (don’t care, not important). The range storage data refers to, for example but not limited to, 1~3, 2~5, 1~8, "1~2 or 5", etc. When the search data matches the storage data, the search result is a match, and vice versa. To illustrate by searching the first row of FIG. 1B, when the search data is 2 and the storage data is 1~3, the search result is a match; when the search data is 5 and the storage data is 2~5, the search result is a match; and, when the search data is a wildcard (1~8) and the storage data is "1~2 or 5", the search result is a match. Therefore, the search result for the first column is a match, and the same applies to the remaining columns.

FIG. 1C shows a schematic diagram of single-bit storage data and range search data. The range search data input by the bit line or word line refers to, for example but not limited to, 1~2, 5~8, 4~5, etc. When the search data matches the storage data, the search result is a match, and vice versa. To illustrate, when the search data is 1~2 and the storage data is 1, the search result is a match; when the search data is 5~8 and the storage data is 5, the search result is a match; and, when the search data is 4~5 and the storage data is 2, the search result is a mismatch. Therefore, the search result for the first row is a mismatch, and the same can be applied to the remaining rows.

In one embodiment of the present case, when a content addressable memory cell includes N (N is a positive integer greater than or equal to 3) flash memory cells, the encoding definition of these N flash memory cells is as follows.

個。 When N flash memory cells are used to represent a ten-digit digital data combination (0, 1, 2, ... N), that is, the CAM memory cell is used to store one of (0, 1, 2, ... N), the N flash memory cells can be encoded as: 1 flash memory cell is a high critical voltage ("0") and (N-1) flash memory cells are low critical voltage ("1"), or, 1 flash memory cell is a low critical voltage ("1") and (N-1) flash memory cells are high critical voltage ("0"), so the total number of combinations is

Piece.

個。 When N flash memory cells are used to represent 2 ten-digit digital data combinations (0 and 1, 0 and 2, 1 and 3, ... (N-1) and N), that is, the CAM memory cell is used to store one of (0 and 1, 0 and 2, 1 and 3, ... (N-1) and N), the N flash memory cells can be encoded as: 2 flash memory cells are high critical voltage ("0") and (N-2) flash memory cells are low critical voltage ("1"), or, 2 flash memory cells are low critical voltage ("1") and (N-2) flash memory cells are high critical voltage ("0"), so the total number of combinations is

Piece.

個。 When N flash memory cells are used to represent three 10-bit digital data combinations (0 and 1 and 2, 0 and 1 and 3, ... (N-2) and (N-1) and N), that is, The CAM memory cell is used to store one of (0 and 1 and 2, 0 and 1 and 3, ... (N-2) and (N-1) and N). The N flash memory cells can be encoded as: 3 flash memory cells are high critical voltage ("0") and (N-3) flash memory cells are low critical voltage ("1"), or 3 flash memory cells are low critical voltage ("1") and (N-3) flash memory cells are high critical voltage ("0"), so the total number of combinations is

Piece.

個。 And so on. When N flash memory cells are used to represent N ten-digit digital data combinations (0 and 1 and 2... and N), that is, when the CAM memory cells are used to store (0 and 1 and 2... and N), the N flash memory cells can be encoded as: N flash memory cells are high critical voltage ("0") and 0 flash memory cells are low critical voltage ("1"), or, N flash memory cells are low critical voltage ("1") and 0 flash memory cells are high critical voltage ("0"), so the total number of combinations is

Piece.

In one embodiment of the present case, when the search data is defined by N (N is a positive integer greater than or equal to 3) search voltages, the encoding definition of these N search voltages is as follows.

個。 When N search voltages are used to represent a ten-digit digital data combination (0, 1, 2, ... N), that is, the search data represents one of (0, 1, 2, ... N), the N search voltages can be encoded as: 1 search voltage is a high search voltage (which can be a voltage of VH, VH2, VD or VS, which will be described below) and (N-1) search voltages are low search voltages (which can be VL, VH1, 0V or 0V, which will be described below), or, 1 search voltage is a low search voltage and (N-1) search voltages are high search voltages. Therefore, the number of combinations is a total of

Piece.

個。 When N search voltages are used to represent 2 combinations of ten-digit digital data (0 and 1, 0 and 2, 1 and 3, ... (N-1) and N), that is, the search data represents one of (0 and 1, 0 and 2, 1 and 3, ... (N-1) and N), the N search voltages can be encoded as: 2 search voltages are high search voltages and (N-2) search voltages are low search voltages, or, 2 search voltages are low search voltages and (N-2) search voltages are high search voltages. Therefore, the total number of combinations is

Piece.

個。 When N search voltages are used to represent three combinations of ten-digit digital data (0 and 1 and 2, 0 and 1 and 3, ... (N-2) and (N-1) and N), that is, the search data represents one of (0 and 1 and 2, 0 and 1 and 3, ... (N-2) and (N-1) and N), the N search voltages can be encoded as: 3 search voltages are high search voltages and (N-3) search voltages are low search voltages, or, 3 search voltages are low search voltages and (N-3) search voltages are high search voltages. Therefore, the total number of combinations is

Piece.

個。 And so on. When N search voltages are used to represent N ten-digit digital data combinations (0 and 1 and 2... and N), that is, the search data represents (0 and 1 and 2... and N), the N search voltages can be encoded as: N search voltages are high search voltages and 0 search voltages are low search voltages, or, N search voltages are low search voltages and 0 search voltages are high search voltages. Therefore, the total number of combinations is

Piece.

First embodiment

In the first embodiment of the present case, in order to realize "range storage and single-bit search", the critical voltage of multiple flash memory cells and the setting of multiple search voltages can be shown in the following Table 1-1. Below, the content addressable memory cell including 4 flash memory cells is used as an example for explanation, but it should be known that the present case is not limited to this.

Table 1-1

Taking Table 1-1 as an example, when the critical voltages of the four flash memory cells are 1101 or 0010, the storage data of the content addressable memory cell is 1; When the four search voltages are HHLH or LLHL, the search data is 1. The rest can be deduced in the same way.

When the stored data is 0,1,2,3 (XX, not important), the search results are matches regardless of the search data. When the stored data is invalid data, the search results are mismatches regardless of the search data. When the search data is the wildcard 0,1,2,3 (XX, WC), the search results are matches regardless of the stored data. When the search data is invalid data, the search results are mismatches regardless of the stored data.

In the first embodiment of the present case, in order to realize "single bit storage and range search", the critical voltages of multiple flash memory cells and the settings of multiple search voltages can be shown in the following Table 1-2.

Second embodiment

FIG. 2A shows a content addressable memory cell 200 according to the second embodiment of the present invention, and its critical voltage distribution diagram.

The content addressable memory cell 200 includes: a plurality of flash memory cells connected in series, wherein the flash memory cells are, for example but not limited to, floating gate memory cells, Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) memory cells, floating dot memory cells, Ferroelectric FET (FeFET) memory cells, Resistive random-access memory (RRAM or ReRAM), Phase-change memory (PCM), conductive-bridging RAM (CBRAM), etc. In FIG. 2A, the content addressable memory cell 200 includes 4 serially connected flash memory cells T1 to T4 as an example for illustration, but it should be noted that the present invention is not limited thereto. In other embodiments of the present invention, the content addressable memory cell 200 includes N serially connected flash memory cells (N is a positive integer greater than or equal to 3).

The gate of the flash memory cell T1 is connected to the word line WL1 to receive the first search voltage SL_1, the gate of the flash memory cell T2 is connected to the word line WL2 to receive the second search voltage SL_2, the gate of the flash memory cell T3 is connected to the word line WL3 to receive the third search voltage SL_3, and the gate of the flash memory cell T4 is connected to the word line WL4 to receive the fourth search voltage SL_4. The source of the flash memory cell T1 is electrically connected to the drain of the flash memory cell T2, and the rest can be deduced accordingly. The drain of the flash memory cell T1 and the source of the flash memory cell T4 are electrically connected to other signal lines (not shown).

The storage data of the content addressable memory cell 200 is determined by the combination of multiple critical voltages of the flash memory cells T1~T4.

As shown in FIG. 2A, in the second embodiment of the present invention, when the flash memory cell has a high reference critical voltage (HVT), the flash memory cell stores logic 0; and when the flash memory cell has a low reference critical voltage (LVT), the flash memory cell stores logic 1. In addition, the reference search voltages VH (H) and VL (L) (VH>VL) represent possible values of the first search voltage SL_1 to the fourth search voltage SL_4.

In the second embodiment of the present case, by encoding the critical voltages of the flash memory cells and encoding the search voltages, "range storage and single bit search" and "single bit storage and range search" can be realized. They will be explained below.

The second embodiment of "range storage and single-bit search"

In the second embodiment of the present case, in order to realize "range storage and single-bit search", the critical voltages of the flash memory cells T1~T4 and the settings of the search voltages SL_1~SL_4 can be shown in the following Table 2-1.

Taking Table 2-1 as an example, when the critical voltages of T1~T4 are 0001 respectively, the storage data of the content addressable memory cell 200 is 1; when the search voltages SL_1~SL_4 are VH, VH, VL, VH respectively, the search data is 1. The rest can be deduced in the same way.

The second embodiment of "single-bit storage and range search"

In the second embodiment of the present case, in order to realize "single bit storage and range search", the critical voltages of the flash memory cells T1~T4 and the settings of the search voltages SL_1~SL_4 can be shown in the following Table 2-2.

Figure 2A also shows the critical voltage distribution diagram according to the second embodiment of the present invention.

In the second embodiment of the present case, the voltage difference between the search voltage and the critical voltage applied to the word line is called the gate overdrive voltage (GO). In the matched state, the gate overdrive voltage exceeds a threshold value, and the transistor provides a cell current; on the contrary, in the unmatched state, the gate overdrive voltage is lower than the threshold value, and the transistor does not provide a cell current. Taking FIG. 2A as an example, the reference search voltages VH and VL can be 6V and 2V respectively, the high reference critical voltage is, for example but not limited to, 6V, and the low reference critical voltage is, for example but not limited to, 2V. The gate overdrive voltage between the reference search voltage VH and the high reference critical voltage is about 2V, which can be regarded as a high gate overdrive voltage; the gate overdrive voltage between the reference search voltage VH and the low reference critical voltage is about 6V, which can be regarded as a high gate overdrive voltage; The gate overdrive voltage between the search voltage VL and the high reference critical voltage is approximately <0V, which can be regarded as a low gate overdrive voltage; the gate overdrive voltage between the reference search voltage VL and the low reference critical voltage is approximately 2V, which can be regarded as a high gate overdrive voltage.

In detail, when the search voltage is a high reference search voltage (VH), regardless of whether the critical voltage of the transistor is a low reference critical voltage (LVT) or a high reference critical voltage (HVT), the gate overdrive voltage of the transistor exceeds the threshold value, so the transistor provides a cell current. When the search voltage is a low reference search voltage (VL), (1) if the critical voltage of the transistor is a low reference critical voltage (LVT), the gate overdrive voltage of the transistor exceeds the threshold value, so the transistor provides a reference cell current; and (2) if the critical voltage of the cell is a high reference critical voltage (HVT), the gate overdrive voltage of the transistor is lower than the threshold value, so the transistor does not provide a cell current.

FIG. 2B shows a schematic diagram of the "range storage and single bit search" operation according to the second embodiment of the present invention. In the memory strings SS21~SS24, the storage data of the content addressable memory cells C21~C28 are shown in FIG. 2B. Here, the search data are 2 and 1 for illustration. The search data are input to the content addressable memory cells C21~C28 through word lines WL21~WL28.

The search data is 2 (the search voltages are VH, VL, VH, VH), the four critical voltages of the content addressable memory cell C21 are 0111 (the range storage data of the content addressable memory cell C21 is 0~2), and the four flash memory cells T1~T4 of the content addressable memory cell C21 all provide cell currents, so the search result of the content addressable memory cell C21 is a match. The search data is 1 (the search voltages are VH, VH, VL, VH), the four critical voltages of the content addressable memory cell C22 are 0010 (the range storage data of the content addressable memory cell C22 is 1), and the four flash memory cells T1~T4 of the content addressable memory cell C22 all provide cell currents, so the search result of the content addressable memory cell C22 is a match. Therefore, the memory string SS21 will generate a matching current to the inductive amplifier SA (also called a current detection circuit or an electrical characteristic detection circuit), indicating that the search result of the memory string SS21 is a match.

Similarly, memory string SS22 will not generate a matching current to the sense amplifier SA, indicating that the search result for memory string SS22 is a mismatch. Memory string SS23 will generate a matching current to the sense amplifier SA, indicating that the search result for memory string SS23 is a match. Memory string SS24 will not generate a matching current to the sense amplifier SA, indicating that the search result for memory string SS24 is a mismatch.

Third embodiment

FIG. 3A shows a CAM cell 300 according to the third embodiment of the present invention and its critical voltage distribution diagram. The circuit architecture of the CAM cell 300 may be the same or similar to that of the CAM cell 200, so its details are omitted here.

As shown in FIG. 3A, in the third embodiment of the present invention, when the flash memory cell has a high reference critical voltage (HVT) (for example, but not limited to, 3~4V), the flash memory cell stores logic 0; and, when the flash memory cell has a low reference critical voltage (LVT) (for example, but not limited to, less than 0V), the flash memory cell stores logic 1. In addition, reference search voltages VH1 and VH2 (VH2>VH1) represent possible values of the first search voltage SL_1 to the fourth search voltage SL_4, wherein VH2 and VH1 are, for example, but not limited to, 8V and 5V.

In the third embodiment of the present case, by encoding the critical voltages of the flash memory cells and encoding the search voltages, "range storage and single bit search" and "single bit storage and range search" can be realized. They will be explained below.

The third embodiment of "range storage and single-bit search"

In the third embodiment of the present case, in order to realize "range storage and single-bit search", the critical voltages of the flash memory cells T1~T4 and the settings of the search voltages SL_1~SL_4 can be shown in the following Table 3-1.

Taking Table 3-1 as an example, when the critical voltages of T1~T4 are 0001 respectively, the storage data of the content addressable memory cell 200 is 1; when the search voltages SL_1~SL_4 are VH2, VH2, VH1, VH2 respectively, the search data is 1. The rest can be deduced in the same way.

The third embodiment of "single-bit storage and range search"

In the third embodiment of the present case, in order to realize "single bit storage and range search", the critical voltages of the flash memory cells T1~T4 and the settings of the search voltages SL_1~SL_4 can be shown in the following Table 3-2.

Table 3-2

Figure 3A also shows the critical voltage distribution diagram according to the third embodiment of the present invention.

When the search voltage is a high reference search voltage (VH2), regardless of whether the critical voltage of the transistor is a low reference critical voltage (LVT) or a high reference critical voltage (HVT), the gate overdrive voltage of the transistor exceeds the threshold value, so the transistor provides a cell current. When the search voltage is a low reference search voltage (VH1), (1) if the critical voltage of the transistor is a low reference critical voltage (LVT), the gate overdrive voltage of the transistor exceeds the threshold value, so the transistor provides a reference cell current; and (2) if the critical voltage of the cell is a high reference critical voltage (HVT), the gate overdrive voltage of the transistor is lower than the threshold value, so the transistor does not provide a cell current.

FIG. 3B shows a schematic diagram of the "range storage and single-bit search" operation according to the third embodiment of the present invention. In the memory strings SS31~SS34, the storage data of the content-addressable memory cells C31~C38 are shown in FIG. 3B. Here, the search data are 2 and 1 for illustration. The search data are input to the content-addressable memory cells C31~C38 through word lines WL31~WL38.

Take memory string SS32 as an example. The search data is 2 (the search voltages are VH2, VH1, VH2, and VH2), and the four critical voltages of content addressable memory cell C33 are 1100 (the range storage data of content addressable memory cell C33 is 2~3). Therefore, the four flash memory cells of content addressable memory cell C33 all provide cell current. The search data is 1 (the search voltages are VH2, VH2, VH1, and VH2), and the four critical voltages of the content addressable memory cell C34 are 0100 (the range storage data of the content addressable memory cell C34 is 2). Therefore, the three flash memory cells T1, T2, and T4 of the content addressable memory cell C34 provide cell currents, but the flash memory cell T3 of the content addressable memory cell C34 does not provide cell currents. Therefore, the sensing result of the sense amplifier SA on the memory string SS32 represents a bit mismatch.

Similarly, the sensing result of the sense amplifier SA on the memory string SS31 represents a full match. The sensing result of the sense amplifier SA on the memory string SS33 represents a full match. The sensing result of the sense amplifier SA on the memory string SS34 represents a two-bit mismatch.

That is, in the third embodiment, when the matching result is a full match, the highest current can be sensed; when the matching result is a partial match (such as a one-bit match, a two-bit match, etc.), a medium current can be sensed; when the matching result is a full mismatch, the lowest current can be sensed.

Fourth embodiment

FIG. 4A shows a content addressable memory cell 400 according to the fourth embodiment of the present invention and its critical voltage distribution diagram. The content addressable memory cell 400 includes four flash memory cells, the gates of which are coupled together. In addition, the source terminals of the four flash memory cells are coupled to the bit lines BL1 to BL4 to receive four search voltages respectively, and the drain terminals of the four flash memory cells are coupled to the source terminals of the four flash memory cells of the next content addressable memory cell.

As shown in FIG. 4A, in the fourth embodiment of the present invention, when the flash memory cell has a high reference critical voltage (HVT), the flash memory cell stores logic 0; and when the flash memory cell has a low reference critical voltage (LVT), the flash memory cell stores logic 1. In addition, the reference search voltage VD and 0V (VD>0V) represent possible values of the first search voltage SL_1 to the fourth search voltage SL_4. For example, but not limited to, VD is close to 1V.

When the content addressable memory cell 400 is to be selected, a selection voltage Vselect (Vselect is between a high reference threshold voltage (HVT) and a low reference threshold voltage (LVT)) is applied to the gates of the four flash memory cells of the selected content addressable memory cell 400 through word lines WL41-44, and a pass voltage Vpass is applied to the gates of the four flash memory cells of the unselected content addressable memory cell 400. For example but not limited to, Vpass is close to 7V. When the selection voltage Vs is applied When the pass voltage Vpass is applied, the four flash memory cells of the content addressable memory cell 400 are all turned on. When the pass voltage Vpass is applied, the four flash memory cells of the content addressable memory cell 400 are all turned on. When the pass voltage Vpass is applied, the four flash memory cells of the content addressable memory cell 400 are all turned on. When the pass voltage Vpass is applied, the four flash memory cells of the content addressable memory cell 400 are all turned on. When the pass voltage Vpass is applied, the four flash memory cells of the content addressable memory cell 400 are all turned on. When the pass voltage Vpass is applied, the four flash memory cells of the content addressable memory cell 400 are all turned on.

In the fourth embodiment of the present case, by encoding the critical voltages of the flash memory cells and encoding the search voltages, "range storage and single bit search" and "single bit storage and range search" can be realized. They will be explained below.

The fourth embodiment of "range storage and single-bit search"

In the fourth embodiment of the present case, in order to realize "range storage and single-bit search", the critical voltages of the flash memory cells T1~T4 and the settings of the search voltages SL_1~SL_4 can be shown in the following Table 4-1.

Taking Table 4-1 as an example, when the critical voltages of T1~T4 are 1101 respectively, the storage data of the content addressable memory cell 400 is 1; when the search voltages SL_1~SL_4 are 0V, 0V, VD, 0V respectively, the search data is 1. The rest can be deduced in the same way.

The fourth embodiment of "single bit storage and range search"

In the fourth embodiment of the present case, in order to realize "single bit storage and range search", the critical voltages of the flash memory cells T1~T4 and the settings of the search voltages SL_1~SL_4 can be shown in the following Table 4-2.

FIG. 4A also shows a critical voltage distribution diagram according to the fourth embodiment of the present invention. In the fourth embodiment of the present invention, when the search data matches the stored data, the content addressable memory cell 400 does not provide a cell current; and when the search data does not match the stored data, the content addressable memory cell 400 provides a cell current.

FIG. 4B and FIG. 4C show schematic diagrams of the "range storage and single bit search" operation according to the fourth embodiment of the present invention. The storage data of the content addressable memory cells are shown in FIG. 4B and FIG. 4C. Here, the search data is 1, 2, 2 for illustration. The search data is input to the content addressable memory cells through bit lines BL1~BL12.

Take the selection of word line WL41 as an example. The search data is 1 (the search voltages are 0V, 0V, VD, and 0V respectively), and the four critical voltages of the first content addressable memory cell are 1101 respectively (the range storage data of the content addressable memory cell is 1). Therefore, the four flash memory cells of the first content addressable memory cell do not provide cell current. The search data is 2 (the search voltages are 0V, VD, 0V, and 0V respectively), and the four critical voltages of the second content addressable memory cell are 1000 (the range of content addressable memory cells is 0 to 2), so none of the four flash memory cells of the second content addressable memory cell provide cell current. The search data is 2 (the search voltages are 0V, VD, 0V, and 0V respectively), and the four critical voltages of the third content addressable memory cell are 0011 (the range of content addressable memory cells is 2 to 3), so none of the four flash memory cells of the third content addressable memory cell provide cell current. Therefore, the detection result of the current detection circuit 410 on the word line WL41 represents full match (no current).

Similarly, in FIG. 4C , the detection result of the current detection circuit 410 on the word line WL43 represents a 2-bit mismatch (current), wherein the first content addressable memory cell and the second content addressable memory cell provide current, while the third content addressable memory cell does not provide current.

In the fourth embodiment, when the matching result is a full match, no current can be sensed; when the matching result is a partial match (such as a one-bit mismatch, a two-bit mismatch, etc.), a medium current can be sensed; when the matching result is a full mismatch, the highest current can be sensed.

Fifth embodiment

FIG. 5A shows a content-addressable memory cell 500 according to the fifth embodiment of the present invention and its critical voltage distribution diagram. The content-addressable memory cell 500 includes four flash memory cells, and the gates of the four flash memory cells are respectively coupled to different word lines WL1-WL4 to receive four search voltages respectively. In addition, the source terminals of the four flash memory cells are coupled to the matching line ML, and the drain terminals of the four flash memory cells are coupled to the ground terminal.

As shown in FIG. 5A, in the fifth embodiment of the present invention, when the flash memory cell has a high reference critical voltage (HVT), the flash memory cell stores logic 0; and when the flash memory cell has a low reference critical voltage (LVT), the flash memory cell stores logic 1. In addition, the reference search voltage VS and 0V (VS>0V) represent possible values of the first search voltage SL_1 to the fourth search voltage SL_4. For example, but not limited to, VS is close to 3V.

When searching for the content addressable memory cell 500, a search voltage is applied to the four flash memory cells of the content addressable memory cell 500 through the word lines WL1-WL4. In addition, each match line ML is coupled to a pre-charge control circuit 501. The pre-charge control circuit 501 is, for example but not limited to, composed of a transistor, wherein the gate of the transistor receives a start voltage VST, the source is coupled to a reference voltage VM, and the drain is coupled to the match line ML. The match line ML is further coupled to a voltage detection circuit 502 (also referred to as an electrical characteristic detection circuit). Before the search starts, the start voltage VST turns on the pre-charge control circuit 501, so that the match line ML is pre-charged to the reference voltage VM.

In the fifth embodiment of the present case, by encoding the critical voltages of the flash memory cells and encoding the search voltages, "range storage and single bit search" and "single bit storage and range search" can be realized. They will be explained below.

The fifth embodiment of "range storage and single-bit search"

In the fifth embodiment of the present case, in order to realize "range storage and single-bit search", the critical voltages of the flash memory cells T1~T4 and the settings of the search voltages SL_1~SL_4 can be shown in the following Table 5-1.

Taking Table 5-1 as an example, when the critical voltages of T1~T4 are 1101 respectively, the storage data of the content addressable memory cell 500 is 1; when the search voltages SL_1~SL_4 are 0V, 0V, VS, 0V respectively, the search data is 1. The rest can be deduced in the same way.

The fifth embodiment of "single bit storage and range search"

In the fifth embodiment of the present case, in order to realize "single bit storage and range search", the critical voltages of the flash memory cells T1~T4 and the settings of the search voltages SL_1~SL_4 can be shown in the following Table 5-2.

FIG. 5A also shows a critical voltage distribution diagram according to the fifth embodiment of the present invention. In the fifth embodiment of the present invention, when the search data matches the stored data, the content addressable memory cell 500 is non-conductive to maintain the matching line voltage; and when the search data does not match the stored data, the content addressable memory cell 500 is conductive to discharge the matching line voltage.

FIG. 5B shows a schematic diagram of the "range storage and single bit search" operation according to the fifth embodiment of the present invention. The storage data of the content addressable memory cells is shown in FIG. 5B. Here, the search data is 1, 2, 2 for illustration. The search data is input to the content addressable memory cells through word lines.

Take the matching line ML1 as an example. When the search data is 1 (the search voltages are 0V, 0V, VS, and 0V respectively), the four critical voltages of the first content addressable memory cell are 1101 respectively (the range storage data of the content addressable memory cell is 1), so the four flash memory cells of the first content addressable memory cell are not turned on. When the search data is 2 (the search voltage is 0V, VS, 0V, 0V), the four critical voltages of the second content addressable memory cell are 1000 (the range of content addressable memory cell storage data is 0~2), so the four flash memory cells of the second content addressable memory cell are not conducting. When the search data is 2 (the search voltage is 0V, VS, 0V, 0V), the four critical voltages of the third content addressable memory cell are 0011 (the range of content addressable memory cell storage data is 2~3), so the four flash memory cells of the third content addressable memory cell are not conducting. Since all content-addressed memory cells on the match line ML1 are not conducting, the match line ML1 will not be discharged. The match line ML1 can be maintained at the reference voltage VM. The search result of the match line ML1 represents a full match (no discharge current).

Similarly, in Figure 5B, two content addressable memory cells on the match line ML2 are turned on, and the match line ML2 is discharged, that is, the search result of the match line ML2 represents a 2-bit mismatch; one content addressable memory cell on the match line MLn is turned on, and the match line MLn is discharged, that is, the search result of the match line MLn represents a 1-bit mismatch. When there are more bit mismatches (more content addressable memory cells are turned on), the discharge speed of the match line is faster.

In the fifth embodiment, the discharge level of the matching line can be used to determine whether the matching result of the matching line is full match, partial match or no match at all.

Sixth embodiment

FIG. 6A and FIG. 6B show the operation schematic diagrams of "range storage and single bit search" and "single bit storage and range search" according to an embodiment of the present invention. In the sixth embodiment of the present invention, by encoding the critical voltages of the flash memory cells and encoding the search voltages, "range storage and single bit search" and "single bit storage and range search" can be realized. In FIG. 6A and FIG. 6B, a content addressable memory cell 600 including 6 flash memory cells is used as an example for explanation, but it should be known that the present invention is not limited to this.

In Figures 6A and 6B, the matching results can be used to find the Hamming distance (HD) between the search data and the stored data.

FIG. 7 is a flow chart of a data search and matching method of a CAM memory device according to an embodiment of the present invention. As shown in FIG. 7, the data search and matching method includes: storing a storage data in a plurality of content-addressable memory strings (710); performing a data search on the content-addressable memory strings using a search data (720); the content-addressable memory strings generating a plurality of memory string currents (730); and detecting the memory string currents or Detecting a plurality of match line voltages of a plurality of match lines coupled to the content addressable memory strings to generate a plurality of search results, wherein the search data and the storage data are a range storage data and a single bit search data, or the search data and the storage data are a single bit storage data and a range search data (740).

In the above embodiments of the present invention, the CAM memory device may be a two-dimensional (2D) flash memory architecture or a three-dimensional (3D) flash memory architecture, which is within the spirit of the present invention.

In an embodiment of the present case, when performing in-memory similarity search, data search and comparison can be completed within one read cycle. With the high storage density of CAM memory devices, the in-memory similarity search of the present embodiment can be used in a variety of fields, such as but not limited to, big-data searching, AI hardware accelerator/classifier, approximate computing, associative memory, solid-state drive (SSD) data management, deoxyribonucleic acid (DNA) matching, data filtering, etc.

In summary, although the present invention has been disclosed as above by the embodiments, it is not intended to limit the present invention. Those with common knowledge in the technical field to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope defined in the attached patent application.

710~740: Steps

Claims (15)

A content-addressable memory device includes: a plurality of content-addressable memory strings; and an electrical characteristic detection circuit coupled to the content-addressable memory strings; wherein, when performing a data search, a search data is compared with a storage data stored in the content-addressable memory strings, the content-addressable memory strings generate a plurality of memory string currents, and the electrical characteristic detection circuit detects the memory string currents or detects a plurality of matching line currents of a plurality of matching lines coupled to the content-addressable memory strings. Press to generate a plurality of search results, each of the CAM strings includes a plurality of CAM cells, wherein the storage data and the search data are a range storage data and a single-bit search data, or the storage data and the search data are a single-bit storage data and a range search data, and when the range storage data includes a plurality of different storage data, the plurality of different storage data are stored in a single CAM cell of the CAM cells. A content-addressable memory device as described in claim 1, wherein when the search data matches the stored data, the electrical characteristic detection circuit detects the memory string current; and when the search data does not match the stored data, the electrical characteristic detection circuit does not detect the memory string current, the range stored data includes a plurality of different continuous or discontinuous stored data, and the range search data includes a plurality of different continuous or discontinuous search data. A content-addressable memory device as described in claim 1, wherein when the search data matches the stored data, the electrical characteristic detection circuit cannot detect the memory string current; and when the search data does not match the stored data, the electrical characteristic detection circuit detects the memory string current. A content-addressable memory device as described in claim 1, wherein the degree of match between the search data and the stored data is determined to be one of the following based on the search results: full match, partial match, and no match. A content-addressable memory device as described in claim 4, wherein when the search data fully matches the stored data, the electrical characteristic detection circuit detects a first memory string current; when the search data partially matches the stored data, the electrical characteristic detection circuit detects a second memory string current; and when the search data does not fully match the data stored in the stored data, the electrical characteristic detection circuit detects a third memory string current, the first memory string current is higher than the second memory string current, and the second memory string current is higher than the third memory string current. A content-addressable memory device as described in claim 4, wherein when the search data fully matches the stored data, the electrical characteristic detection circuit detects a first memory string current; when the search data partially matches the stored data, the electrical characteristic detection circuit detects a second memory string current; and when the search data does not fully match the data stored in the stored data, the electrical characteristic detection circuit detects a third memory string current, the first memory string current is lower than the second memory string current, and the second memory string current is lower than the third memory string current. The content addressable memory device as described in claim 4 further includes: a precharge control circuit coupled to the match lines, and before the search starts, the precharge control circuit precharges the match lines to a reference voltage; wherein when the search data fully matches the stored data, the electrical characteristic detection circuit detects a first match line voltage; when the search data When the search data partially matches the stored data, the electrical characteristic detection circuit detects a second match line voltage; and when the search data does not match the stored data at all, the electrical characteristic detection circuit detects a third match line voltage, the first match line voltage is higher than the second match line voltage, and the second match line voltage is higher than the third match line voltage. A data search and matching method for a content-addressable memory device, comprising: Storing a storage data in a plurality of content-addressable memory strings, each of which includes a plurality of content-addressable memory cells; performing a data search on the content-addressable memory strings using a search data; the content-addressable memory strings generate a plurality of memory string currents; detecting the memory string currents or detecting a plurality of matching lines coupled to the content-addressable memory strings; A plurality of matching line voltages are connected to generate a plurality of search results, wherein the storage data and the search data are a range storage data and a single-bit search data, or the storage data and the search data are a single-bit storage data and a range search data, and when the range storage data includes a plurality of different storage data, the plurality of different storage data are stored in a single content addressable memory cell of the content addressable memory cells. A data search and comparison method for a content-addressable memory device as described in claim 8, wherein when the search data matches the stored data, an electrical characteristic detection circuit detects the memory string current; and when the search data does not match the stored data, the electrical characteristic detection circuit cannot detect the memory string current, the range stored data includes a plurality of different continuous or discontinuous stored data, and the range search data includes a plurality of different continuous or discontinuous search data. A data search and matching method for a content-addressable memory device as described in claim 8, wherein: When the search data matches the stored data, an electrical characteristic detection circuit cannot detect the memory string current; and when the search data does not match the stored data, the electrical characteristic detection circuit detects the memory string current. A data search and comparison method for a content-addressable memory device as described in claim 8, wherein the degree of match between the search data and the stored data is determined to be one of the following based on the search results: full match, partial match, and no match. A data search and comparison method for a content-addressable memory device as described in claim 11, wherein when the search data fully matches the stored data, an electrical characteristic detection circuit detects a first memory string current; when the search data partially matches the stored data, the electrical characteristic detection circuit detects a second memory string current; and when the search data does not fully match the data stored in the stored data, the electrical characteristic detection circuit detects a third memory string current, the first memory string current is higher than the second memory string current, and the second memory string current is higher than the third memory string current. A data search and comparison method for a content-addressable memory device as described in claim 11, wherein when the search data fully matches the stored data, an electrical characteristic detection circuit detects a first memory string current; when the search data partially matches the stored data, the electrical characteristic detection circuit detects a second memory string current; and when the search data does not fully match the data stored in the stored data, the electrical characteristic detection circuit detects a third memory string current, the first memory string current is lower than the second memory string current, and the second memory string current is lower than the third memory string current. A data search and comparison method for a content-addressable memory device as described in claim 11, wherein the match lines are precharged to a reference voltage before the search begins; when the search data fully matches the stored data, a first match line voltage is detected; when the search data partially matches the stored data, a second match line voltage is detected; and when the search data does not fully match the stored data, a third match line voltage is detected, the first match line voltage is higher than the second match line voltage, and the second match line voltage is higher than the third match line voltage. A content-addressable memory cell comprises: a plurality of memory cells, wherein the memory cells are connected in series, and a plurality of search voltages representing a search data are input to a plurality of control terminals of the memory cells; or the control terminals of the memory cells receive a selection voltage or a pass voltage, and the search voltages are input to a plurality of first terminals of the memory cells through a plurality of signal lines; or the control terminals of the memory cells are coupled to a plurality of word lines to receive the search voltages, and the control terminals of the memory cells receive a selection voltage or a pass voltage, and the search voltages are input to a plurality of first terminals of the memory cells through a plurality of signal lines. The first terminals of the memory cells are further coupled to a matching line and a precharge control circuit, and the second terminals of the memory cells are coupled to the ground terminal, wherein a storage data and the search data of the content-addressable memory cell are a range storage data and a single-bit search data, or the storage data and the search data are a single-bit storage data and a range search data, and when the range storage data includes a plurality of different storage data, the plurality of different storage data are stored in the content-addressable memory cell.

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