Memory edge cell

The present application is a divisional of U.S. application Ser. No. 13/025,872, filed Feb. 11, 2011, the disclosure of which is incorporated herein by reference in its entirety.

The present disclosure is related to a memory edge cell.

Generally, when a memory cell in a Static Random Access Memory (SRAM) enters a standby mode, to reduce the leakage current, the operational voltage of the memory is reduced to a voltage sufficient to retain the data, commonly called the “retaining voltage.” In many approaches, the power management circuitry that controls the retaining voltage is implemented by logic devices that need area overheads and that do not work well with devices manufactured by a memory process. For example, in an approach, the SRAM retaining voltage is generated by a diode connected logic device. Because SRAMs and logic devices have different manufacturing process variations, the retaining voltage while functioning for the logic device can cause loss of data in the SRAM. In another approach, the retaining voltage is generated by a voltage regulator, which requires a longer wake up time and consumes lots of power. In another approach, the SRAM edge cell requires a large die area for a short bit line in segmented SRAMs and register files.

The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and claims.

FIG. 1 is a block diagram of a memory, in accordance with some embodiments.

FIG. 2 is a detailed circuit of a power management edge cell of the memory in FIG. 1 , in accordance with a first embodiment.

FIG. 3 is a detailed circuit of a power management edge cell of the memory in FIG. 1 , in accordance with a second embodiment.

FIG. 4 is a table summarizing the operation of the circuit in FIG. 3 , in accordance with some embodiments.

FIG. 5 is a detailed circuit of a power management edge cell of the memory in FIG. 1 , in accordance with a third embodiment.

FIG. 6 is a table summarizing the operation of the circuit in FIG. 5 , in accordance with some embodiments.

FIG. 7 is a detailed circuit of a power management edge cell of the memory in FIG. 1 , in accordance with a fourth embodiment.

FIG. 8 is a table summarizing the operation of the circuit in FIG. 7 , in accordance with some embodiments.

FIG. 9 is a diagram of a circuit illustrating a connection of a power management cell and a memory cell of the memory in FIG. 1 , in accordance with some embodiments.

Like reference symbols in the various drawings indicate like elements.

Embodiments, or examples, illustrated in the drawings are disclosed below using specific language. It will nevertheless be understood that the embodiments and examples are not intended to be limiting. Any alterations and modifications in the disclosed embodiments, and any further applications of the principles disclosed in this document are contemplated as would normally occur to one of ordinary skill in the pertinent art. Reference numbers may be repeated throughout the embodiments, but they do not require that feature(s) of one embodiment apply to another embodiment, even if they share the same reference number.

Some embodiments have one or a combination of the following features and/or advantages. The power management edge cell in accordance with some embodiments is about one-half smaller than an edge cell in another approach. The power management edge cell includes mechanisms to generate a voltage reference for the retaining voltage with a reduced current leakage. The front-end layers of the power management edge cell are the same as the front-end layers of the memory cell. As a result, the model of a memory cell can be used to simulate the power management edge cell.

Exemplary Memory

FIG. 1 is a block diagram of a memory or SRAM 100 , in accordance with some embodiments.

Memory 100 includes a plurality of banks. For illustration, two memory banks MB- 1 and MB- 2 are shown, and the details of only memory bank MB- 1 are labeled. A memory bank includes a plurality of segments. For illustration, memory bank MB- 1 is shown having two segments SEG- 1 and SEG- 2 .

A plurality of strap cells STPCELL is shared between two memory arrays. In FIG. 1 , because strap cells STPCELL are shared between two arrays of two memory banks MB- 1 and MB- 2 , strap cells STPCELL are effectively shared between two memory banks MB- 1 and MB- 2 .

The edges of a memory bank include a plurality of either strap cells STPCELL or edge cells ECELL. For example, the top edge of memory bank MB- 1 includes a plurality of strap cells STPCELL, and the bottom edge of memory bank MB- 1 includes a plurality of edge cells ECELL.

The edges of memory 100 include a plurality of edge cells ECELL at the respective top edge and bottom edge of memory 100 .

A memory array includes a plurality of memory cells or bit cells arranged in rows and columns. Each of segments SEG- 1 and SEG- 2 includes a respective memory array. Each memory array includes a plurality of memory cells MC (not labeled).

The edges of a memory cell array include a plurality of either edge cells ECELL, power management edge cells PMCELL, or strap cells STPCELL. For example, the top edge of the memory array of SEG- 1 includes a first plurality of power management edge cells, and the bottom edge of the memory array of SEG- 1 includes a first plurality of edge cells ECELL. In contrast, the top edge of the memory array of SEG- 2 includes a plurality of strap cells STPCELL while the bottom edge of the memory array of SEG- 2 includes a second plurality of power management edge cells PMCELL. In some embodiments, edge cells ECELL, strap cells STPCELL and power management cells PMCELL create an environment at the boundary or edges of the memory arrays to protect the inside memory cells MC. From a column perspective, a column of cells in segment SEG- 1 includes a power management cell PMCELL at the top of the column, a plurality of memory cells MC below the power management cell PMCELL, and an edge cell ECELL at the bottom of the column. Similarly, a column of cells in segment SEG- 2 includes a strap cell STCELL at the top of the column, a plurality of memory cells MC below the strap cell STCELL, and a power management cell PMCELL at the bottom of the column.

In some embodiments, a power management cell PMCELL and a memory cell MC have the same transistors (illustrated in FIG. 9 ) with different configurations. As a result, a power management cell PMCELL and a memory cell MC have the same layout below a metal one layer. In some embodiments, the metal layers include the metal one layer below a metal two layer, which, in turn, is below a metal three layer, etc. The layers below the metal one layer are also commonly called the front-end layers, and include, for example, a contact area, a poly area, a diffusion area, etc. Front end layers are distinguished from back-end layers, which refer to the metal layers and the vias. Stated differently, a power management cell PMCELL and a memory cell MC have the same front-end layers. As a result, the simulation model for a memory cell MC can be used to simulate the power management edge cell PMCELL. Further, without the power management edge cells PMCELL at the edge of a memory array, memory cells MC at the edge of the memory array would not have the same performance as memory cells MC that are not at the edge of the memory array due to the nature of the manufacturing process.

In some embodiments, a power management edge cell PMCELL provides ground reference voltages for a retaining voltage with a minimum leakage current because the retaining voltage is referenced to a raised voltage VSSI (illustrated in FIG. 2 ).

A row of local input/output circuits LIO is shared between two segments and includes circuitry for controlling the respective segments.

Power Management Edge Cell

1 st Embodiment

FIG. 2 is a diagram of a circuit 200 illustrating a power management edge cell PMCELL, in accordance with a first embodiment.

Nodes NVSS and NVSSI have respective voltages VSS and VSSI that are provided to memory cells MC in memory 100 , the details of which are explained with reference to FIG. 9 . For illustration purposes, memory cells MC coupled to circuit 200 are called memory cells MCPM. Further, because the internal ground nodes NVSSIM of memory cells MCPM illustrated in FIG. 9 are coupled to nodes NVSSI of power management edge cell PMCELL, internal ground nodes NVSSIM and nodes NVSSI are used interchangeably in this document.

The voltage level of node NVSSI is at either voltage VSS of node NVSS when transistors N 4 and N 2 are on or at a raised voltage at the drain of transistor N 1 functioning as a diode, which is explained below. As a result, memory cells MCPM have a ground reference voltage level at either voltage VSSI or voltage VSS. Stated differently, a power management edge cell PMCELL provides the bias or reference voltage to the internal ground nodes NVSSIM of memory cells MCPM, and therefore serves as a power management cell for memory 100 .

The pair of PMOS transistors P 1 and P 2 , and the pair of NMOS transistors N 1 and N 2 correspond to a pair of PMOS transistors and a pair of NMOS transistors that form a cross latch in a memory cell MC. The gates of transistors P 1 and N 1 and the drain of transistor P 2 are coupled together. The gates of transistors P 2 and N 2 and the drain of transistor P 1 are coupled together. The drain and the source of transistor P 1 , the source of transistor P 2 , and a supply voltage source having operational voltage VDD are coupled together. Because the drain of transistor P 1 is coupled to the gates of PMOS transistor P 2 and NMOS transistor N 2 being at voltage VDD, transistor P 2 is always off while transistor N 2 is always on.

The drain and the source of transistor N 3 are functionally interchangeable, i.e., the drain functions as the source and the source functions as the drain. Similarly, the drain and the source of transistor N 4 are functionally interchangeable.

The drains of transistors P 2 and N 2 and the source of transistor N 4 are coupled together. The drain of transistor N 4 is coupled to node NVSS having voltage VSS. The gate of transistor N 4 is coupled to a signal line SLPB. In effect, transistor N 4 is controlled by the signal on line SLPB, which, for simplicity, is also called signal SLPB. When signal SLPB is applied with a High, transistor N 4 is on. But when signal SLPB is applied with a Low, transistor N 4 is off.

The source of transistor N 2 , node NVSSI having voltage VSSI, and the gate and the drain of transistor N 3 are coupled together. Node NVSSI is coupled to the internal ground node NVSSIM of a memory cell MCPM. The source of transistor N 3 is coupled to a bit line BL, which couples the memory cells in a column. The drain of transistor N 3 is coupled to the drain of transistor N 1 . Because the gate of transistor N 3 is coupled to node NVSSI having voltage VSSI at a low logic level, transistor N 3 is always off.

When transistor N 4 is on, the voltage at the source of transistor N 4 is the same as voltage VSS of node NVSS at the drain of transistor N 4 . Because transistor N 2 is always on, node NVSSI at the source of transistor N 2 has the same voltage as that of at the drain of transistor N 2 . Because the source of transistor N 4 is coupled to the drain of transistor N 2 , node NVSSI at the source of transistor N 2 is at voltage VSS of node NVSS at the drain of transistor N 4 . In contrast, when transistor N 4 is off, transistor N 4 functions as an open circuit, and is electrically disconnected from the drains of transistors N 2 and P 2 . Because transistor N 2 is always on, the drain and the source of transistor N 2 are at the same voltage level. Because the drain of transistor N 2 is coupled to the gate of transistor N 1 , and the source of transistor N 2 is coupled to the drain of transistor N 1 through the gate of transistor N 3 , the drain and the gate of transistor N 1 are at the same voltage level. In effect, transistor N 1 functions as a diode. As a result, node NVSSI coupled to the drain of transistor N 1 is at a voltage level equal to a diode voltage drop of transistor N 1 functioning as a diode. Stated differently, the ground reference of circuit 200 and of the memory cells MCPM coupled to circuit 200 is raised by a diode voltage of the transistor functioning as a diode N 1 . In some embodiments, the retaining voltage of memory 100 is based on the raised reference voltage of node NVSSI. In some embodiments, the diode voltage of transistor N 1 is about the threshold voltage of transistor N 1 , which is about 250 mV for a 0.85 V VDD transistor.

Power Management Edge Cell

2 nd Embodiment

FIG. 3 is a diagram of a circuit 300 illustrating a power management edge cell PMCELL, in accordance with a second embodiment.

Compared with circuit 200 , circuit 300 additionally includes transistor N 5 controlled by signal SDB. The drain of transistor N 5 is coupled to the source of transistor N 1 . The source of transistor N 5 is coupled to ground.

In some embodiments, transistors P 1 , P 2 , N 1 , N 2 , N 3 , and N 4 are manufactured by a “memory” manufacturing process, which refers to a manufacturing process used to manufacture memory devices. In contrast, transistor N 5 is manufactured by a “logic” manufacturing process, which refers to the process used to manufacture logic devices. For illustration purposes, a transistor manufactured by a memory process is called a memory transistor, while a transistor manufactured by a logic process is called a logic transistor. Consequentially, transistor N 5 is called a logic transistor. In some embodiments, memory transistors have threshold voltages different from those of logic transistors.

Transistor N 5 acts as a power switch. When transistor N 5 is off, transistor N 5 functions as an open circuit. If transistor N 4 is off, circuit 200 is shut down because there is no ground reference voltage for transistors N 4 , N 2 , and N 1 . Explained differently, internal ground node NVSSI is floating. In effect, all data stored in the memory cells MC working with circuit 200 are destroyed.

When transistor N 5 is on, the drain of transistor N 5 is at the same low voltage level or ground at the source of transistor N 5 . Because the source of transistor N 1 is coupled to the drain of transistor N 5 , the source of transistor N 1 is also at the ground level. In effect, transistor N 5 provides the ground path for transistor N 1 . Explained differently, the source of transistor N 1 is electrically coupled to ground at the source of transistor N 5 . As a result, circuit 300 functions in a similar manner as circuit 200 . That is, when transistor N 5 is on and transistor N 4 is off, node NVSSI is raised by the diode voltage of transistor N 1 functioning as a diode as explained above.

When transistor N 4 is on, the voltage level at the source of transistor N 4 is pulled to the VSS voltage level at the drain of transistor N 4 . Because transistor N 2 is always on, the voltage level at the drain and at node NVSSI at the source of transistor N 2 are the same. Because the source of transistor N 4 is coupled to the drain of transistor N 2 , the voltage level at node NVSSI at the source of transistor N 2 is at voltage VSS at the drain of transistor N 4 . In some embodiments, when transistor N 4 is on, transistor N 5 is prohibited from being turned off.

FIG. 4 is a table 400 summarizing the operation of circuit 300 , in accordance with some embodiments.

On line ( 1 ), when both transistor N 4 and N 5 are on, circuit 300 sets memory cells MCPM in the idle or read or write mode because internal ground node NVSSI is at voltage VSS.

On line ( 2 ), when transistor N 4 is off and transistor N 5 is on, memory cells MCPM are in a sleep mode because internal ground node NVSSI is raised by the diode voltage of transistor N 1 .

On line ( 3 ), when both transistors N 4 and N 5 are off, memory cells MCPM are shut down because there is no ground reference for transistors N 1 and N 2 .

On line ( 4 ), circuit 300 is prohibited from having transistor N 4 on while transistor N 5 is off.

Power Management Edge Cell

3 rd Embodiment

FIG. 5 is a detailed circuit 500 illustrating a power management edge cell PMCELL, in accordance with a third embodiment.

Compared with circuit 300 , circuit 500 additionally includes transistor N 6 controlled by signal LSLPB. The drain of transistor N 6 is coupled to node NVSSI. The source of transistor N 6 is coupled to ground or node NVSS. In some embodiments, transistor N 6 is a logic transistor.

When transistor N 6 is on, node NVSSI at the drain of transistor N 6 is pulled to the VSS voltage level at the source of transistor N 6 . In effect, the internal ground nodes NVSSI of memory cells MCPM are at the normal low voltage level VSS. In some embodiments, transistor N 6 is a logic transistor and has a resistance less than the combined resistance of both transistors N 2 and N 4 . As a result, transistor N 6 provides a stronger current to pull node NVSSI at the drain of transistor N 6 to voltage VSS at the source of transistor N 6 . When transistor N 6 is off, transistor N 6 functions as an open circuit. As a result, circuit 500 functions in the same manner as circuit 300 that does not include transistor N 6 .

FIG. 6 is a table 600 summarizing the operation of circuit 500 , in accordance with some embodiments.

On line ( 1 ), when transistor N 5 is off, transistors N 4 and N 6 are forced to be off. Circuit 500 is in the shut down mode.

On line ( 2 ), when transistor N 5 is on and transistor N 4 is off, transistor N 6 is forced to be off. Circuit 500 is in the sleep mode. Node NVSSI has a raised voltage level at voltage VSSI through diode N 1 . Transistor N 5 provides the ground path for transistor N 1 .

On line ( 3 ), when transistor N 5 is on, transistor N 4 is on, and transistor N 6 is off. Circuit 500 is in the Idle/Read/Write mode similar to line ( 1 ) in table 400 . Voltage VSSI at node NVSSI at the source of transistor N 2 is at the same VSS voltage level at the source of transistor N 4 .

On line ( 4 ), when transistors N 5 , N 6 , and N 4 are on, circuit 500 is in the turbo mode. Node NVSSI at the drain of transistor N 6 is pulled to the VSS voltage level at the source of transistor N 6 .

Power Management Edge Cell

4 th Embodiment

FIG. 7 is a detailed circuit 700 illustrating a power management edge cell PMCELL, in accordance with a fourth embodiment.

Circuit 700 includes circuit 100 coupled with a circuit 710 . Circuit 710 has similar transistors as those in circuit 100 with different configurations. Transistors P 1 - 2 , P 2 - 2 , N 1 - 2 , N 2 - 2 , N 3 - 2 and N 4 - 2 of circuit 710 correspond to respective transistors P 1 , P 2 , N 1 , N 2 , N 3 , and N 4 of circuit 100 . In addition, transistor N 3 - 2 functions in a manner similar to transistor N 5 in circuit 500 . As a result, transistor N 3 - 2 in circuit 710 can be considered equivalent to transistor N 5 in circuit 500 . For illustration purposes, transistors N 3 - 2 and N 5 are used interchangeably. Circuit 700 also includes transistor N 6 that functions in the same manner as transistor N 6 in circuit 500 .

The gate, the drain, and the source of transistor P 1 - 2 , voltage VDD, and the gate of transistor N 1 - 2 are coupled together. Because the gate of transistor N 1 - 2 is coupled to voltage VDD, transistor N 1 - 2 is always on. As a result, the drain and the source of transistor N 1 - 2 are at the same voltage level. Because the source of transistor N 1 is coupled to the drain of transistor N 1 - 2 , the voltage level at the source of transistor N 1 is at the same voltage level at the source of transistor N 1 - 2 . When transistor N 5 is on, the drain and the source of transistor N 5 are at the same voltage level. Because the source of transistor N 1 - 2 is coupled to the drain of transistor N 5 , when transistor N 5 is on, the source of transistor N 1 - 2 is at the same VSS voltage level at the source of transistor N 5 . In effect, when transistor N 5 is on, the source of transistor N 1 is at voltage VSS of node NVSS.

The gate, the drain and the source of transistor P 2 - 2 , voltage VDD, and the gate of transistor N 2 - 2 are coupled together. Because the gate of transistor N 2 - 2 is at voltage VDD, transistor N 2 - 2 is always on. As a result, the drain and the source of transistor N 2 - 2 are at the same level.

Signal SLPB at the gates of transistors N 4 and N 4 - 2 turns on or off transistors N 4 and N 4 - 2 at the same time. When transistors N 4 and N 4 - 2 are on (e.g., by activating signal SLPB), the drain and the source of transistor N 4 are at the same voltage level, and the drain and the source of transistor N 4 - 2 are at the same voltage level. Because the drains of transistors N 4 and N 4 - 2 are coupled together, the source of transistor N 4 - 2 is at the same voltage level at the source of transistor N 4 . Because transistor N 2 is always on, the drain and the source of transistor N 2 are at the same level. Consequently, node NVSSI at the source of transistor N 2 is at the same level at the source of transistor N 4 . In effect, when transistors N 4 and N 4 - 2 are on, node NVSSI at the source of transistor N 2 is at voltage VSS of node NVSS at the source of transistor N 2 - 2 .

Compared with circuit 500 , circuit 700 has less leakage current. In circuit 700 , while node NVSSI at the source of transistor N 2 is pulled to voltage VSS at the source of transistor N 2 - 2 , the current flows from node NVSSI through four transistors N 2 , N 4 , N 4 - 2 , and N 2 - 2 to ground. In contrast, in circuit 500 , while node NVSSI at the source of transistor N 2 is pulled to voltage VSS at the drain of transistor N 4 , the current flows through two transistors N 2 and N 4 to ground. In effect, transistors N 4 - 2 and N 2 - 2 provide additional resistance in circuit 700 to reduce the current flow or the leakage current.

Similar to circuit 500 , when transistor N 6 is on, node NVSSI at the drain of transistor N 6 is pulled to voltage VSS of node NVSS at the source of transistor N 6 . Stated differently, node NVSSI is at voltage VSS. When transistor N 6 is off, transistor N 6 acts as an open circuit. Node NVSSI at the source of transistor N 2 is electrically disconnected from the drain of transistor N 6 , and is affected by other transistors through the source of transistor N 2 and the gate and the drain of transistor N 3 .

FIG. 8 is a table 800 summarizing the operation of circuit 700 , in accordance with some embodiments. Table 800 is similar to table 600 except that in table 600 transistor N 4 functions individually while, in table 800 , transistors N 4 and N 4 - 2 are turned on or off at the same time.

On line ( 1 ), when transistor N 5 is off, transistors N 4 , N 4 - 2 , and N 6 are forced to be off. Circuit 700 is in the shut down mode because transistor N 5 acts as an open circuit and there is no ground for transistor N 1 - 2 , N 1 , N 4 and N 2 - 2 .

On line ( 2 ), when transistor N 5 is on and transistors N 4 and N 4 - 2 are off, transistor N 6 is forced to be off. Circuit 700 is in the sleep mode. Node NVSSI has a raised voltage level at voltage VSSI through diode N 1 . Because transistor N 5 is on, voltage VSS at the source of transistor N 5 serves as a current path for the current at the source of transistor N 1 flowing through transistor N 1 - 2 and N 5 .

On line ( 3 ), when transistor N 5 is on, transistors N 4 and N 4 - 2 are on, and transistor N 6 is off. Circuit 700 is in the Idle/Read/Write mode. Voltage VSSI at node NVSSI at the source of transistor N 2 is at the same voltage level at the source of transistor N 2 - 2 through the drain of transistor N 2 coupled to the source of transistor N 4 , the drain of transistor N 4 coupled to the drain of transistor N 4 - 2 , and the source of transistor N 4 - 2 coupled to the drain of transistor N 2 - 2 .

On line ( 4 ), when transistors N 5 , N 6 , and N 4 are on, circuit 700 is in the turbo mode. Node NVSSI at the drain of transistor N 6 is pulled to the VSS voltage level at the source of transistor N 6 . In some embodiments, the resistance of transistor N 6 is much less compared to the resistance of cascaded transistors N 2 - 2 , N 4 - 2 , N 4 and N 2 . At the same time, node NVSSI at the source of transistor N 2 is at the same voltage level at the source of transistor N 2 - 2 through the drain of transistor N 2 coupled to the source of transistor N 4 , the drain of transistor N 4 coupled to the drain of transistor N 4 - 2 , and the source of transistor N 4 - 2 coupled to the drain of transistor N 2 - 2 . In effect, node NVSSI is at voltage VSS at both the source of transistor N 6 and the source of transistor N 2 - 2 .

Exemplary Connection of a Memory Cell and a Power Management Cell

FIG. 9 is a diagram of a circuit 900 illustrating a connection of a memory cell MC and a power management edge cell 200 , in accordance with some embodiments.

Memory cell MC includes transistors P 1 M, P 2 M, N 1 M, N 2 M, N 3 M, N 4 M corresponding to transistors P 1 , P 2 , N 1 , N 2 , N 3 , and N 4 of cell 200 , respectively. Transistor P 1 M, P 2 M, and N 1 M, and N 2 M form a cross latch for memory cell MC as should be recognizable by persons of ordinary skill in the art. Word line WL of memory cell MC corresponds to signal line SLPB of cell 200 . In some embodiments, an available memory cell MC is used to form a power management edge cell 200 . For example, the word line WL is used to form signal SLPB. The gate of transistor N 3 M is disconnected from word line WL and is connected to the source of transistor N 2 M. The source of transistor N 2 M is disconnected from ground. The drain of transistor P 1 M is disconnected from the drain of transistor N 1 M, and is connected to the source of transistor P 1 M. The drain of transistor N 4 M is disconnected from bit line BLB, and is connected to ground node NVSS, etc.

Internal ground node NVSSIM of memory cell MC is coupled to node NVSSI of power management edge cell 200 . In effect, node NVSS of cell 200 serves as the ground or VSS node for memory cell MC. As a result, the ground reference of memory cell MC is either at the normal voltage VSS of node NVSS or at the raised voltage VSSI at node NVSSI when voltage VSSI is raised as explained above.

FIG. 9 is used for illustration. Additional memory cells MC are coupled to FIG. 9 as should be recognizable by persons of ordinary skill in the art. For example, internal ground nodes NVSSIM of the additional memory cells MC in a column are also coupled to node NVSSI of cell 200 . Transistors N 3 M of the additional memory cells MC are coupled to bit line BL while transistors N 4 M of the additional memory cells MC are coupled to bit line BLB, etc. Circuit 900 is in fact a column of cells of memory array of memory 100 . The memory cell MC at the bottom of the column is coupled either to a power management cell PMCELL, a strap cell STPCELL, or an edge cell ECELL as should be recognizable by persons of ordinary skill in the art. Circuit 200 is used for illustration in circuit 900 . Other power management edge cells, including cells 300 , 500 , or 700 being used in place of circuit 200 , are within the scope of various embodiments.

A number of embodiments have been described. It will nevertheless be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, the various transistors being shown as a particular dopant type (e.g., N-type or P-type Metal Oxide Semiconductor, or NMOS and PMOS) are for illustration purposes, embodiments of the disclosure are not limited to a particular type. Selecting different dopant types is within the scope of various embodiments. The logic level (e.g., Low or High) of various signals used in the above description is also for illustration purposes. Various embodiments are not limited to a particular level when a signal is activated and/or deactivated. Selecting different logic levels is within the scope of various embodiments.

In accordance with at least one embodiment, a column of a memory includes a first edge cell and at least one memory cell. The first edge cell is located at a first edge of the column and includes a first edge cell reference node and a second edge cell reference node. Each of the at least one memory cells includes a first memory reference node. The first edge cell reference node is coupled to respective first memory reference nodes of the at least one memory cell. The second edge cell reference node serves as second memory reference nodes of the at least one memory cell. Front-end layers of the first edge cell are the same as front-end layers of a memory cell of the at least one memory cell.

In accordance with another embodiment, a memory circuit includes an input/output circuit coupled to a bit line, an edge cell coupled to the bit line, and at least one memory cell coupled to the bit line. The edge cell includes a first transistor, a second transistor, and a third transistor. The first transistor has a source coupled to a first voltage node, a drain coupled to the source, and a gate. The second transistor has a source coupled to a second voltage node, a gate coupled to the gate of the first transistor, and a drain coupled to a reference voltage node. The third transistor has a source coupled to the reference voltage node, a gate coupled to the source of the third transistor, and a drain coupled to the bit line. The edge cell is located between the at least one memory cell and the input/output circuit.

In accordance with another embodiment, a memory circuit includes an input/output circuit coupled to a bit line, a first edge cell coupled to the bit line, a second edge cell located adjacent to the first edge cell, and at least one memory cell coupled to the bit line. The first edge cell includes a first transistor, a second transistor, and a third transistor. The first transistor has a source coupled to a first voltage node, a drain coupled to the source, and a gate. The second transistor has a source coupled to a second voltage node, a gate coupled to the gate of the first transistor, and a drain. The third transistor has a source coupled to a reference voltage node, a gate coupled to the source of the third transistor, and a drain coupled to the bit line. The second edge cell includes a fourth transistor, a fifth transistor, and a sixth transistor. The fourth transistor has a source coupled to the first voltage node, a drain coupled to the source, and a gate coupled to the first voltage node. The fifth transistor has a source, a drain coupled to the source of the second transistor, and a gate coupled to the first voltage node. The sixth transistor has a source coupled to the second voltage node, a gate, and a drain coupled to the source of the fifth transistor. The first and second edge cells are located between the at least one memory cell and the input/output circuit.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art would appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art would also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.