Patent Application
20240135976
The present invention relates to a memory design, and more particularly, to a memory with fly-bitlines that work with single-ended sensing and an associated memory access method.
For a variety of applications, a cache storage element can be used to temporarily retain data for further processing. The traditional approach for this cache storage element is by using single-port static random access memory (SRAM) bit-cells (e.g., six-transistor (6T) single-port SRAM bit-cells) or two-port SRAM bit-cells (e.g., 8T two-port SRAM bit-cells). In a single-port SRAM bit-cell, normally, either of read operation and write operation is performed in one access through a complementary bitline pair that consists of two bitlines. When the read operation is performed on the single-port SRAM bit-cell, two bitlines of the complementary bitline pair are pre-charged to the supply voltage, a wordline is driven high after pre-charging is turned off, one of the bitlines is pulled down according to a stored value, and a differential sense amplifier is activated to capture the stored value according to a differential voltage presented at the complementary bitline pair. However, the differential sense amplifier requires complicated pre-charging timing control and pass-gate timing control. Furthermore, the differential sense amplifier has a high gate count, thus leading to large chip area as well as high power consumption.
Thus, there is a need for an innovative memory design which can have small chip area, low power consumption, and/or simple timing control.
One of the objectives of the claimed invention is to provide a memory with fly-bitlines that work with single-ended sensing and an associated memory access method.
According to a first aspect of the present invention, an exemplary memory is disclosed. The exemplary memory includes a memory array and a single-ended sense amplifier circuit. The memory array includes a plurality of wordlines, a plurality of bitlines, and a plurality of memory cells. Each of the plurality of wordlines includes a first bitline and a second bitline, wherein the first bitline is routed on a first metal layer but not a second metal layer, and the second bitline is routed on the first metal layer and the second metal layer, where the second metal layer is different from the first metal layer. Each of the plurality of memory cells is coupled to one of the plurality of wordlines. The plurality of memory cells include a first group of memory cells, coupled to the first bitline; and a second group of memory cells, coupled to the second bitline, wherein the first group of memory cells and the second group of memory cells are located at a same column. The single-ended sense amplifier circuit is arranged to perform a read operation upon a target memory cell through single-ended sensing when a selected wordline is enabled, wherein the target memory cell is selected from the first group of memory cells and the second group of memory cells.
According to a second aspect of the present invention, an exemplary method for accessing a memory array is disclosed. The memory array includes a plurality of wordlines, a plurality of bitlines, and a plurality of memory cells, wherein the bitlines comprise a first bitline routed on a first metal layer but not a second metal layer that is different from the first metal layer, and a second bitline routed on the first metal layer and the second metal layer, each of the plurality of memory cells is coupled to one of the plurality of wordlines, the plurality of memory cells comprise a first group of memory cells coupled to the first bitline, and a second group of memory cells coupled to the second bitline, and the first group of memory cells and the second group of memory cells are located at a same column. The exemplary method includes: selecting a target memory cell from the first group of memory cells and the second group of memory cells; and in response to a selected wordline being enabled, performing a read operation upon the target memory cell through single-ended sensing.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Certain terms are used throughout the following description and claims, which refer to particular components. As one skilled in the art will appreciate, electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not in function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
The memory array 102 includes a plurality of memory cells arranged in a two-dimensional (2D) array with a plurality of rows and a plurality of columns. As shown in
In this embodiment, each of the memory cells may have a single-port SRAM architecture for storing one bit, such as a 6T bit-cell architecture. As a person skilled in the pertinent art can readily understand details of the typical 6T SRAM bit-cell, further description is omitted here for brevity. The memory array 102 includes a plurality of wordlines WL_0-WL_N−1, one complementary bitline pair consisting of bitlines BL and BLB, and another complementary bitline pair consisting of bitlines BL_fly and BLB_fly, where the wordlines WL_0-WL_N−1 correspond to different memory cell rows, respectively, and the bitlines BL, BLB, BL_fly, BLB_fly correspond to the same memory cell column.
In this embodiment, a fly-bitline (FBL) structure can be adopted to improve the memory access speed. For example, each of the bitlines BL and BLB is routed on a first metal layer (e.g., M0) but not a second metal layer (e.g., M2), and each of the bitlines BL_fly and BLB_fly is an FBL that has a first segment routed on the first metal layer (e.g., M0) and a second segment routed on the second metal layer (e.g., M2), where the second segment routed on the second metal layer (e.g., M2) acts as an extension of the first segment routed on the first metal layer (e.g., M0) and is across the memory cells 106_i+1-106_N−1.
As shown in
In this embodiment, the single-ended sense amplifier circuit 105 is arranged to perform a read operation upon a target memory cell through single-ended sensing when a selected wordline is enabled. For example, the target memory cell is selected from the first group of memory cells 108 and the second group of memory cells 110 located at the same memory cell column, and the selected wordline is one of the wordlines WL_0-WL_N−1. Hence, when the selected wordline WL j {j=0, 1, . . . , N−1} is enabled, the single-ended sense amplifier circuit 105 is activated to capture a stored data bit of the target memory cell 106_j {j=0, 1, . . . , N−1} through single-ended sensing. That is, the single-ended sense amplifier circuit 105 does not need to receive voltage levels at two bitlines BL and BLB (or BL_fly and BLB_fly) of the same complementary bitline pair to capture a stored data bit of the target memory cell. Instead, the single-ended sense amplifier circuit 105 is capable of capturing a stored data bit of the target memory cell by referring to a voltage level at one of two bitlines of a complementary bitline pair that is connected to the target memory cell.
In this embodiment, the single-ended sense amplifier circuit 105 may include a logic gate circuit (e.g., NAND gate) 112 and an output latch circuit 114. The logic gate circuit 112 is arranged to receive two single-ended input signals. For example, the logic gate circuit 112 may have a first input node coupled to one bitline BLB and a second input node coupled to another bitline BLB_fly, where the bitlines BLB and BLB_fly may be connected to SRAM cells at the same column of the memory array. For another example, the logic gate circuit 112 may have a first input node coupled to one bitline BL and a second input node coupled to another bitline BL_fly, where the bitlines BL and BL_fly may be connected to SRAM cells at the same column of the memory array. It should be noted that the logic gate circuit 112 may be implemented by a NAND gate or other logic gate, depending upon actual design considerations. The output latch circuit 114 has an input node coupled to the output node of the logic gate circuit 112, and an output node arranged to output a read-out data DO of the target memory cell.
Please refer to
In this embodiment, the single-ended sense amplifier circuit 200 includes a NAND gate 202 and an output latch circuit 204. One input node of the NAND gate 202 (i.e., gate terminal of one P-channel metal-oxide-semiconductor transistor) is coupled to the bitline BL, and the other input node of the NAND gate 202 (i.e., gate terminal of another P-channel metal-oxide-semiconductor transistor) is coupled to the bitline BL_fly, where the bitlines BL and BL_fly may be connected to SRAM cells at the same column of the memory array. Suppose that the selected memory cell is one of the memory cells 106_i+1-106_N−1 coupled to the complementary bitline pair consisting of bitlines BL and BLB, and stores a data bit of “0”. During a read period of one cycle of the memory clock CK, pre-charging is applied to bitlines BL, BLB, BL_fly, BLB_fly (i.e., BL=VDD, BLB=VDD, BL_fly=VDD, and BLB_fly=VDD) and then turned off, a selected wordline WL of the selected memory cell is driven high by an enable pulse to allow the selected memory cell (which stores “0”) to pull down the bitline BL that connected to the selected memory cell, and the single-ended sense amplifier circuit 200 is activated by a complementary control signal pair consisting of output latch signals OUTEN and OUTENb. When the bitline BL is developed and becomes lower than a trip point of the NAND gate 202, the NAND gate output signal DOC rises and then the read-out signal DO falls. It should be noted that the access time is decided by firing of the selected wordline WL and the voltage developing speed of the bitline BL if the output latch signals OUTEN and OUTENb are fired earlier than the bitline BL develops. It should be noted that, since the single-ended sense amplifier circuit 105 (or 200) is fully implemented within a global I/O circuit of the memory 100, no additional buffer(s) are needed between the logic gate circuit 112 (or NAND gate 202) and the output latch circuit 114 (or 204).
Alternatively, the single-ended sense amplifier circuit 200 may be properly modified to have two single-ended input signals obtained from bitlines BLB and BLB_fly. To put it simply, the circuit design shown in
Compared to a typical differential sense amplifier circuit, the single-ended sense amplifier circuit 105/200 that works with FBL has a simple control design and a lower gate count, which leads to smaller chip area as well as lower power consumption. The single-ended sense amplifier circuit 105/200 is shown having a logic gate circuit and an output latch circuit. However, this is for illustrative purposes only, and is not meant to be a limitation of the present invention. In practice, any single-ended sensing scheme may be employed by the single-ended sense amplifier circuit 105 to works with FBL used by the memory array 102. These alternative designs all fall within the scope of the present invention.
Since impedance of the bitline BL_fly/BLB_fly may not be the same as that of the bitline BL/BLB due to the fact that bitline BL_fly/BLB_fly are further routed on the second metal layer (e.g., M2), access speed of the memory cells 106_0-106_N−1 is constrained by the access speed of memory cells 106_0-106_i connected to the bitline BL_fly/BLB_fly. To address this issue, the present invention further proposes using an imbalanced FBL/non-FBL load to compensate speed. For example, a cell number of the first group of memory cells 108 (i.e., non-FBL load) may be different from a cell number of the second group of memory cells 110 (i.e., FBL load).
In above embodiments, each of the memory cells has a single-port SRAM architecture for storing one bit, such as a 6T bit-cell architecture. However, this is for illustrative purposes only, and is not meant to be a limitation of the present invention. The same single-ended sensing concept may be applied to a memory array using two-port memory cells and fly-bitlines.
The memory array 602 includes a plurality of memory cells arranged in a 2D array with a plurality of rows and a plurality of columns. As shown in
In this embodiment, each of the memory cells may have a two-port SRAM architecture for storing one bit, such as an 8T bit-cell architecture. As a person skilled in the pertinent art can readily understand details of the typical 8T SRAM bit-cell, further description is omitted here for brevity. The memory array 602 includes a plurality of read wordlines RWL_0-RWL_N−1 (which are used in read operations of 8T SRAM bit-cells), a plurality of write wordlines WWL_0-WWL_N−1 (which are used in write operations of 8T SRAM bit-cells), a complementary write bitline pair consisting of write bitlines WBL and WBLB (which are used in write operations of 8T SRAM bit-cells, and are not used in read operations of 8T SRAM bit-cells), a complementary write bitline pair consisting of write bitlines WBL_fly and WBLB_fly (which are used in write operations of 8T SRAM bit-cells, and are not used in read operations of 8T SRAM bit-cells), a read bitline RBL (which is used in read operations of 8T SRAM bit-cells, and is not used in write operation of 8T SRAM bit-cells), and a read bitline RBL_fly (which is used in read operations of 8T SRAM bit-cells, and is not used in write operations of 8T SRAM bit-cells), where a read wordline RWL_j and a write wordline WWL_j (j={0, 1, . . . , N−1}) correspond to a same memory cell row, and the bitlines WBL, WBLB, WBL_fly, WBLB_fly, RBL, RBL_fly correspond to a same memory cell column.
In this embodiment, an FBL structure can be adopted to improve the memory access speed. For example, each of the bitlines WBL, WBLB, and RBL is routed on a first metal layer (e.g., M0) but not a second metal layer (e.g., M2), and each of the bitlines WBL_fly, WBLB_fly, and RBL_fly is an FBL that has a first segment routed on the first metal layer (e.g., M0) and a second segment routed on a second metal layer (e.g., M2), where the second segment routed on the second metal layer (e.g., M2) acts as an extension of the first segment routed on the first metal layer (e.g., M0) and is across the memory cells 606_i+1-606_N−1.
As shown in
In this embodiment, the single-ended sense amplifier circuit 605 is arranged to perform a read operation upon a target memory cell through single-ended sensing when a selected read wordline is enabled. For example, the target memory cell is selected from the first group of memory cells 608 and the second group of memory cells 610 located at the same memory cell column, and the selected read wordline is one of the read wordlines RWL_0-RWL_N−1.
In this embodiment, the single-ended sense amplifier circuit 605 may include a logic gate circuit (e.g., NAND gate) 612 and an output latch circuit 614. The logic gate circuit 612 is arranged to receive two single-ended input signals. For example, the logic gate circuit 612 may have a first input node coupled to one bitline RBL and a second input node coupled to another bitline RBL_fly, where the bitlines RBL and RBL_fly may be connected to SRAM cells at the same column of the memory array. It should be noted that the logic gate circuit 612 may be implemented by a NAND gate or other logic gate, depending upon actual design considerations. The output latch circuit 614 has an input node coupled to the output node of the logic gate circuit 612, and an output node arranged to output a read-out data DO of the target memory cell. Since a person skilled in the art can readily understand details of the single-ended sense amplifier circuit 605 that works with FBL after reading above paragraphs directed to the single-ended sense amplifier circuit 105/200, further description is omitted here for brevity.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 63/380,598, filed on Oct. 24, 2022. The content of the application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63380598 | Oct 2022 | US |
