阅读说明：本技术 能够减少读取时间的存储系统 (Memory system capable of reducing read time ) 是由 陈纬荣 汤强 于 2019-04-30 设计创作，主要内容包括：一种偏置电路包括充电电流再现单元、单元电流再现单元、电流比较器以及位线偏置发生器。所述充电电流再现单元根据流经电压偏置晶体管的充电电流来生成充电参考电压。所述单元电流再现单元根据流经共源晶体管的单元电流来生成单元参考电压。所述电流比较器包括用于根据所述充电参考电压生成复制充电电流的第一电流发生器以及用于根据所述单元参考电压生成复制单元电流的第二电流发生器。所述位线偏置发生器根据所述复制充电电流和所述复制单元电流之间的差异生成位线偏置电压,以控制页缓冲器对位线进行充电。(A bias circuit includes a charge current reproducing unit, a cell current reproducing unit, a current comparator, and a bit line bias generator. The charging current reproducing unit generates a charging reference voltage according to a charging current flowing through a voltage bias transistor. The cell current reproduction unit generates a cell reference voltage according to a cell current flowing through the common-source transistor. The current comparator includes a first current generator for generating a replica charging current from the charging reference voltage and a second current generator for generating a replica cell current from the cell reference voltage. The bit line bias generator generates a bit line bias voltage according to a difference between the replica charge current and the replica cell current to control a page buffer to charge a bit line.)

1. A storage system, comprising:

a plurality of first memory cells coupled to a first bit line;

a voltage bias transistor having a first terminal configured to receive a first system voltage, a second terminal, and a control terminal;

a first page buffer coupled to the first bit line and the second terminal of the voltage bias transistor;

a common-source transistor having a first terminal coupled to the first bit line, a second terminal configured to receive a second system voltage, and a control terminal; and

a bias circuit, the bias circuit comprising:

a charging current reproduction unit coupled to the voltage bias transistor and configured to generate a charging reference voltage according to a charging current flowing through the voltage bias transistor;

a cell current reproduction unit coupled to the common-source transistor and configured to generate a cell reference voltage according to a cell current flowing through the common-source transistor;

a current comparator coupled to the charging current reproduction unit and the cell current reproduction unit; and

a bit line bias generator coupled to the current comparator and the first page buffer and configured to generate and adjust a bit line bias voltage according to a charge state of the first bit line.

2. The memory system of claim 1, wherein the current comparator comprises:

a first current generator configured to generate a first replica charging current from the charging reference voltage; and

a second current generator configured to generate a first replica cell current from the cell reference voltage.

3. The memory system of claim 2, wherein the bit line bias generator is configured to detect the charge state of the first bit line by a difference between the first replica charge current and the first replica cell current.

4. The storage system of claim 2, wherein:

the bit line bias generator increases the bit line bias voltage when the first replica charge current is greater than the first replica cell current; and is

The bit line bias generator maintains the bit line bias voltage when the first replica charge current is substantially equal to the first replica cell current.

5. The memory system according to claim 1, wherein the first page buffer comprises:

a first transistor having a first terminal coupled to the second terminal of the voltage bias transistor, a second terminal, and a control terminal configured to receive a precharge control signal;

a second transistor having a first terminal coupled to the second terminal of the first transistor, a second terminal, and a control terminal configured to receive a clamping control signal;

a third transistor having a first terminal coupled to the second terminal of the second transistor, a second terminal coupled to the first bit line, and a control terminal configured to receive the bit line bias voltage;

a fourth transistor having a first terminal coupled to the second terminal of the second transistor, a second terminal coupled to a sense amplifier, and a control terminal configured to receive a sense control signal; and

a fifth transistor having a first terminal coupled to the second terminal of the first transistor, a second terminal coupled to the second terminal of the fourth transistor, and a control terminal configured to receive a precharge select signal.

6. The storage system according to claim 1, wherein the charging current reproducing unit includes:

a sixth transistor having a first terminal configured to receive the first system voltage, a second terminal, and a control terminal coupled to the control terminal of the voltage bias transistor;

a first operational amplifier having a positive input terminal coupled to the second terminal of the sixth transistor, a negative input terminal coupled to the second terminal of the voltage bias transistor, and an output terminal configured to output the charging reference voltage; and

a seventh transistor having a first terminal coupled to the second terminal of the sixth transistor, a second terminal configured to receive the second system voltage, and a control terminal coupled to the output terminal of the first operational amplifier.

7. The memory system according to claim 6, wherein the cell current reproduction unit includes:

an eighth transistor having a first terminal configured to receive the first system voltage, a second terminal, and a control terminal;

a second operational amplifier having a positive input terminal coupled to the second terminal of the eighth transistor, a negative input terminal coupled to the first bit line, and an output terminal coupled to the control terminal of the eighth transistor and configured to output the cell reference voltage; and

a ninth transistor having a first terminal coupled to the second terminal of the eighth transistor, a second terminal configured to receive the second system voltage, and a control terminal coupled to the control terminal of the common-source transistor.

8. The storage system of claim 7, wherein:

the first current generator comprises a tenth transistor having a first terminal, a second terminal configured to receive the second system voltage, and a control terminal configured to receive the charging reference voltage; and is

The second current generator includes an eleventh transistor having a first terminal configured to receive the first system voltage, a second terminal coupled to the first terminal of the tenth transistor, and a control terminal configured to receive the cell reference voltage.

9. The storage system of claim 8, wherein:

the tenth transistor and the seventh transistor are N-type transistors; and is

The eleventh transistor and the eighth transistor are P-type transistors.

10. The memory system of claim 8, wherein the bit line bias generator comprises:

a third operational amplifier having a positive input terminal configured to receive a second bias voltage, a negative input terminal coupled to the first terminal of the tenth transistor, and an output terminal configured to output the bit line bias voltage;

a twelfth transistor having a first terminal coupled to the output terminal of the third operational amplifier, a second terminal coupled to the negative input terminal of the third operational amplifier, and a control terminal coupled to the first terminal of the twelfth transistor; and

a resistor having a first terminal coupled to the second terminal of the twelfth transistor and a second terminal configured to receive the second system voltage.

11. The memory system of claim 2, wherein the current comparator further comprises:

a third current generator configured to generate a second replica charging current from the charging reference voltage;

a fourth current generator configured to generate a second replica cell current from the cell reference voltage; and

an inverter having input terminals coupled to the third and fourth current generators and an output terminal configured to output a sense indication signal according to a difference between the second replica charging current and the second replica cell current.

12. The storage system of claim 1, further comprising:

a plurality of second memory cells coupled to a second bit line; and

a second page buffer coupled to the second bit line, the second terminal of the voltage bias transistor, the first terminal of the common source transistor, and the bit line bias generator.

13. A bias circuit, comprising:

a charging current reproduction unit configured to be coupled to a voltage bias transistor and generate a charging reference voltage according to a charging current flowing through the voltage bias transistor;

a cell current reproduction unit configured to be coupled to a common-source transistor and generate a cell reference voltage according to a cell current flowing through the common-source transistor;

a current comparator coupled to the charging current reproduction unit and the cell current reproduction unit, the current comparator comprising:

a bit line bias generator coupled to the current comparator and configured to be coupled to a page buffer and to generate and adjust a bit line bias voltage according to a charging state of a bit line to control the page buffer to charge the bit line.

14. The bias circuit of claim 13, wherein the current comparator comprises:

a first current generator configured to generate a first replica charging current from the charging reference voltage; and

a second current generator configured to generate a first replica cell current from the cell reference voltage.

15. The biasing circuit of claim 14, wherein the bit line bias generator is configured to detect the charge state of the bit line by a difference between the first replica charge current and the first replica cell current.

16. The bias circuit of claim 14, wherein:

the bit line bias generator increases the bit line bias voltage when the first replica charge current is greater than the first replica cell current; and is

The bit line bias generator maintains the bit line bias voltage when the first replica charge current is substantially equal to the first replica cell current.

17. The bias circuit according to claim 13, wherein the charging current reproducing unit comprises:

a first transistor having a first terminal configured to receive a first system voltage, a second terminal, and a control terminal coupled to the control terminal of the voltage bias transistor;

a first operational amplifier having a positive input terminal coupled to the second terminal of the first transistor, a negative input terminal coupled to the second terminal of the voltage bias transistor, and an output terminal configured to output the charging reference voltage; and

a second transistor having a first terminal coupled to the second terminal of the first transistor, a second terminal configured to receive a second system voltage, and a control terminal coupled to the output terminal of the first operational amplifier.

18. The bias circuit of claim 17, wherein the cell current reproducing unit comprises:

a third transistor having a first terminal configured to receive the first system voltage, a second terminal, and a control terminal;

a second operational amplifier having a positive input terminal coupled to the second terminal of the third transistor, a negative input terminal coupled to the bit line, and an output terminal coupled to the control terminal of the third transistor and configured to output the cell reference voltage; and

a fourth transistor having a first terminal coupled to the second terminal of the third transistor, a second terminal configured to receive the second system voltage, and a control terminal coupled to the control terminal of the common-source transistor.

19. The bias circuit of claim 18, wherein:

the first current generator comprises a fifth transistor having a first terminal, a second terminal configured to receive the second system voltage, and a control terminal configured to receive the charging reference voltage; and is

The second current generator includes a sixth transistor having a first terminal configured to receive the first system voltage, a second terminal coupled to the first terminal of the fifth transistor, and a control terminal configured to receive the cell reference voltage.

20. The bias circuit of claim 19, wherein:

the fifth transistor and the second transistor are N-type transistors; and is

The sixth transistor and the third transistor are P-type transistors.

21. The bias circuit of claim 20 wherein the bit line bias generator comprises:

a third operational amplifier having a positive input terminal configured to receive a second bias voltage, a negative input terminal coupled to the first terminal of the fifth transistor, and an output terminal configured to output the bit line bias voltage;

a seventh transistor having a first terminal coupled to the output terminal of the third operational amplifier, a second terminal coupled to the negative input terminal of the third operational amplifier, and a control terminal coupled to the first terminal of the seventh transistor; and

a resistor having a first terminal coupled to the second terminal of the seventh transistor and a second terminal configured to receive the second system voltage.

22. The biasing circuit of claim 14, wherein the current comparator further comprises:

a third current generator configured to generate a second replica charging current from the charging reference voltage;

a fourth current generator configured to generate a second replica cell current from the cell reference voltage; and

an inverter having input terminals coupled to the third and fourth current generators and an output terminal configured to output a sense indication signal according to a difference between the second replica charging current and the second replica cell current.

Technical Field

The present invention relates to a memory system, and more particularly, to a memory system capable of reducing a read time.

Background

In a memory system, data stored in a memory cell is typically read by sensing a data voltage on a bit line caused by the memory cell. For example, in a NAND memory read sequence, to read data stored in a memory cell, a bit line coupled to the memory cell may first be precharged to a predetermined level. After the voltage of the bit line has been established, the word line coupled to the memory cell may be raised to cause the memory cell to generate a current in accordance with the data stored in the memory cell. If the memory cell has not been programmed, the memory cell may generate a significant current that causes the voltage of the bit line to be pulled down. Otherwise, if the memory cell has been programmed, the memory cell will not generate any current or will only generate a negligible current, so that the voltage of the bit line will remain at a similar level. Accordingly, by sensing the voltage of the bit line, data stored in the memory cell can be read.

However, the setup time of the bit line will be a large fraction of the total read time, since the bit line is resistive and capacitive due to unavoidable parasitic resistors and capacitors. Furthermore, because the resistance and capacitance characteristics are unpredictable and process-dependent, the set-up times required for different memory cells are also different. Therefore, a worst-case settling time is always applied to ensure sensing accuracy. In addition, in the related art, the bit line is precharged using a master-slave transistor controlled by a predetermined voltage. In this case, as the voltage of the bit line approaches the desired level, the charging capability may decrease, which also increases the read time.

Disclosure of Invention

One embodiment of the invention discloses a storage system. The memory system includes a plurality of memory cells, a voltage bias transistor, a page buffer, a common source transistor, and a bias circuit.

The first memory cell is coupled to a bit line. The voltage bias transistor has a first terminal for receiving a first system voltage, a second terminal, and a control terminal for receiving a first bias voltage.

The page buffer is coupled to the bit line and a second terminal of the voltage bias transistor. The page buffer charges a first bit line to a first system voltage according to a bit line bias voltage during a precharge operation, and forms a sensing path from the first bit line to a sense amplifier during a sensing operation.

The common-source transistor has a first terminal coupled to the first bit line, a second terminal for receiving a second system voltage less than the first system voltage, and a control terminal for receiving a control signal.

The bias circuit includes a charging current reproducing unit, a cell current reproducing unit, a current comparator, and a bit line bias generator. The charging current reproduction unit is coupled to the voltage bias transistor. The charging current reproducing unit generates a charging reference voltage according to a charging current flowing through the voltage bias transistor. The cell current reproduction unit is coupled to the common source transistor. The unit current reproduction unit generates a unit reference voltage according to a unit current flowing through the common source transistor.

The current comparator is coupled to the charging current reproduction unit and the cell current reproduction unit. The current comparator includes a first current generator and a second current generator. The first current generator generates a replica charging current according to the charging reference voltage, and the second current generator generates a replica cell current according to the cell reference voltage.

The bit line bias generator is coupled to the current comparator and the first page buffer. The bit line bias generator generates the bit line bias voltage according to a difference between a first replica charge current and a first replica cell current.

Another embodiment of the invention discloses a bias circuit. The bias circuit includes a charging current reproducing unit, a cell current reproducing unit, a current comparator, and a bit line bias generator.

The charging current reproduction unit is coupled to a voltage bias transistor and generates a charging reference voltage according to a charging current flowing through the voltage bias transistor. The cell current reproduction unit is coupled to a common source transistor and generates a cell reference voltage according to a cell current flowing through the common source transistor.

The current comparator is coupled to the charging current reproduction unit and the cell current reproduction unit. The current comparator includes a first current generator and a second current generator. The first current generator generates a replica charging current according to the charging reference voltage, and the second current generator generates a replica cell current according to the cell reference voltage.

The bit line bias generator is coupled to the current comparator and a page buffer, and generates a bit line bias voltage to control the page buffer to charge a bit line according to a difference between the replica charge current and the replica cell current.

A plurality of first memory cells are coupled to the bit line, the voltage bias transistor having a first terminal for receiving a first system voltage, a second terminal, and a control terminal for receiving a first bias voltage. The page buffer is coupled to the bit line and a second terminal of the voltage bias transistor, and charges the bit line to a first system voltage according to the bit line bias voltage during a precharge operation. The common-source transistor has a first terminal coupled to the bit line, a second terminal for receiving a second system voltage less than the first system voltage, and a control terminal for receiving a control signal.

These and other objects of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.

Drawings

FIG. 1 illustrates a storage system according to one embodiment of the invention.

Fig. 2 shows a bias circuit according to an embodiment of the invention.

Detailed Description

FIG. 1 illustrates a storage system 100 according to one embodiment of the invention. The memory system 100 includes a plurality of memory cells MC (1,1) to MC (M, N), a voltage bias transistor 110, page buffers 1201 to 120N, a common source transistor 120, and a bias circuit 130, where M and N are positive integers.

In fig. 1, memory cells MC (1,1) to MC (M, N) are arranged in an array. For example, memory cells MC (1,1) through MC (M,1) may be coupled to bit line BL1, and memory cells MC (1, N) through MC (M, N) may be coupled to bit line BLN. Further, the memory cells MC (1,1) to MC (1, N) may be coupled to the word line WL1, and the memory cells MC (M,1) to MC (M, N) may be coupled to the word line WLM.

The voltage bias transistor 110 has a first terminal for receiving a first system voltage VS1, a second terminal, and a control terminal for receiving a first bias voltage VB 1. The first bias voltage VB1 may turn on the voltage bias transistor 110 to charge the bit lines BL1 to BLN through the page buffers 1201 to 120N.

The page buffers 1201 to 120N may have the same structure. For example, the page buffer 1201 may be coupled to the bit line BL1 and the second terminal of the voltage bias transistor 110. The page buffer 1201 may charge the bit line BL1 to the first system voltage VS1 according to the bit line bias voltage VBLB during the precharge operation, and may form a sensing path from the bit line BL1 to the sense amplifier during the sensing operation.

In fig. 1, the page buffer 1201 includes transistors M1 to M5. The transistor M1 has a first terminal coupled to the second terminal of the voltage bias transistor 110, a second terminal, and a first terminal for receiving a precharge control signal SIG_C1The control terminal of (1). The transistor M2 has a first terminal coupled to the second terminal of the transistor M1, a second terminal, and a first terminal for receiving a clamp control signal SIG_C2The control terminal of (1). The transistor M3 has a first terminal coupled to the second terminal of the second transistor M2, a second terminal coupled to the bit line BL1, and a control terminal for receiving the bit line bias voltage VBLB. The transistor M4 has a first terminal coupled to the second terminal of the transistor M2, a couplingA second terminal coupled to the sense amplifier for sensing and for receiving a sense control signal SIG_C3The control terminal of (1). The transistor M5 has a first terminal coupled to the second terminal of the transistor M1, a second terminal coupled to the second terminal of the transistor M4, and a first terminal for receiving a precharge select signal SIG_C4The control terminal of (1).

During the precharge operation, transistors M1 and M2 will be turned on, and transistor M3 will also be turned on to charge bit line BL 1. In some embodiments, the memory system 100 may further include high voltage pass transistors 1501 to 150N, and the page buffers 1201 to 120N may be coupled to the bit lines BL1 to BLN through the high voltage pass transistors 1501 to 150N, respectively. In this case, high voltage pass transistor 1501 will also be driven by pass signal SIG during the precharge operation of bit line BL1_HVAnd conducting.

Also, during the sensing operation, the transistors M1, M2, and M3 may be turned off, and the transistor M4 may be turned on, so that the voltage of the bit line BL may be sensed by the sense amplifier. Transistor M5 may be used to select the bit line to be precharged as desired.

The common-source transistor 130 has a first terminal coupled to the bit lines BL 1-BLN, a second terminal for receiving a second system voltage VS2 that is less than the first system voltage VS1, and a first terminal for receiving a control signal SIG_ACSThe control terminal of (1).

During the precharge operation of the bit line BL1, the voltage bias transistor 110 and the common source transistor 130 may be turned on, and may also turn on the transistors M1, M2, and M3 of the page buffer 1201. Therefore, the bit line BL1 may be precharged. However, in the prior art, as the voltage of the bit line BL1 increases, the gate-to-source voltage applied to the transistor M3 will decrease, thereby impairing the charging capability and increasing the time required for precharging. In the memory system 100, to solve this problem, the bias circuit 140 may be used to generate and adjust the bit line bias voltage VBLB to control the transistor M3 according to the situation of the precharge operation.

Fig. 2 also shows a bias circuit 140 according to one embodiment of the invention. The bias circuit 140 includes a charge current reproduction unit 142, a cell current reproduction unit 144, a current comparator 146, and a bit line bias generator 148.

The charging current reproduction unit 142 is coupled to the voltage bias transistor 110, and may be according to the charging current I flowing through the voltage bias transistor 110_chgGenerating a charging reference voltage V_ref1。

The unit current reproduction unit 144 is coupled to the common-source transistor 130, and may be according to a unit current I flowing through the common-source transistor 130_cellGenerating a cell reference voltage V_ref2。

The current comparator 146 is coupled to the charging current reproduction unit 142 and the cell current reproduction unit 144. The current comparator 146 includes a first current generator 146A and a second current generator 146B. The first current generator 146A may be based on the charging reference voltage V_ref1Generating a replica charging current I_rchg1The second current generator 146B can be based on the cell reference voltage V_ref2Generating a replica cell current I_rcell1。

The bit line bias generator 148 is coupled to the current comparator 146 and the page buffers 1201 to 120N. The bit line bias generator 148 may be based on the replica charge current I_rchg1And replica cell current I_rcell1The difference between them generates the bit line bias voltage VBLB.

In some embodiments, the charging current I_chgMay flow to a parasitic capacitor on the bit lines BL 1-BLN at the beginning of the precharge operation, while the rest of the charging current I_chgWill flow through common source transistor 130. Then, when the parasitic capacitor is charged, the charging current I_chgWill all flow through common source transistor 130.

That is, at the start of the precharge operation, the charging current I_chgWill be greater than the cell current I_cellThus, the charging current I is reproduced_rchg1Should be greater than the replica cell current I_rcell1. In this case, the charging current I is replicated_rchg1And replica cell current I_rcell1The difference between will cause the bit line bias generator 148 to increase the bit line bias voltage VBLB, fromAnd transistor M3 may be fully turned on to improve charging capability.

Thereafter, when the parasitic capacitor is fully charged, the charging current I is replicated_rchg1Will be substantially equal to the replica cell current I_rcell1. In this case, it may mean that the bit line BL1 has been charged, and therefore the bit line bias generator 148 will hold the bit line bias voltage VBLB, and the sensing operation may be performed accordingly.

In some embodiments, the current comparator 146 may further include a third current generator 146C, a fourth current generator 146D, and a circuit for generating the sensing indication signal SIG_IDCTInverter 146E. The third current generator 146C may be based on the charging reference voltage V_ref1Generating a replica charging current I_rchg2The fourth current generator 146D may be based on the cell reference voltage V_ref2Generating a replica cell current I_rcell2. The inverter 146E has input terminals coupled to the third current generator 146C and the fourth current generator 146D, and is configured to be charged according to the replica charging current I_rchg2And replica cell current I_rcell2Outputs the sense indication signal SIG_IDCTAn output terminal of (1). In this case, when the charging current I is copied_rchg2And replica cell current I_rcell2Becomes zero, sensing indication signal SIG_IDCTIs to be inverted, and the sensing operation may be indicated by the inverted sensing indication signal SIG_IDCTAnd is triggered accordingly.

Since the bit line bias generator 148 can immediately adjust the bit line bias voltage VBLB according to the charge states of the bit lines BL1 through BLN, the charging capability can be maintained strong during the precharge operation. Moreover, since the charging current I can be copied_rchg1And replica cell current I_rcell1The difference between them detects the charged state of the bit lines BL1 through BLN, so the precharge operation may be terminated and the sensing operation may be triggered once the bit lines BL1 through BLN are precharged. That is, the precharge time can be optimized, and the precharge operation can be controlled without being affected by process variations.

In fig. 2, a charging current reproducing unit 142 includes transistors M6, M7, and an operational amplifier OP 1. The transistor M6 has a first terminal for receiving a first system voltage VS1, a second terminal, and a control terminal coupled to the control terminal of the voltage bias transistor 110. The operational amplifier OP1 has a positive input terminal coupled to the second terminal of the transistor M6, a negative input terminal coupled to the second terminal of the voltage bias transistor 110, and a means for outputting a charging reference voltage V_ref1An output terminal of (1). The transistor M7 has a first terminal coupled to the second terminal of the transistor M6, a second terminal for receiving the second system voltage VS2, and a control terminal coupled to the output terminal of the operational amplifier OP 1.

In this case, the operational amplifier OP1 can ensure that the transistor M6 is biased under the same conditions as the voltage bias transistor 110. Therefore, the charging current reproducing unit 142 can bias the transistor 110 according to the charging current I flowing through the voltage_chgA reproduction current is generated.

Similarly, the cell current reproduction unit 144 includes transistors M8, M9, and an operational amplifier OP 2. The transistor M8 has a first terminal for receiving a first system voltage VS1, a second terminal, and a control terminal. An operational amplifier OP2 has a positive input terminal coupled to the second terminal of transistor M8, a negative input terminal coupled to the bit lines BL 1-BLN, and a control terminal coupled to transistor M8 for outputting a cell reference voltage V_ref2An output terminal of (1). The transistor M9 has a first terminal coupled to the second terminal of the transistor M8, a second terminal for receiving a second system voltage VS2, and a control terminal coupled to the control terminal of the common-source transistor 130.

In this case, the operational amplifier OP2 may ensure that the transistor M9 and the common source transistor 130 are biased under the same conditions. Therefore, the cell current reproduction unit 144 can be based on the cell current I flowing through the common source transistor 130_cellA reproduction current is generated.

In fig. 2, the first current generator 146A comprises a transistor M10, the transistor M10 having a first terminal, a second terminal for receiving the second system voltage VS2, and a second terminal for receiving the charging reference voltage V_ref1Control ofAnd a terminal. In addition, the second current generator 146B includes a transistor M11, the transistor M11 having a first terminal for receiving the first system voltage VS1, a second terminal coupled to the first terminal of the transistor M10, and a second terminal for receiving the cell reference voltage V_ref2The control terminal of (1).

In addition, in fig. 2, the transistors M7 and M10 are N-type transistors, and the transistors M8 and M11 are P-type transistors. In this case, the charging reference voltage V is used_ref1Transistor M10 will be biased under the same conditions as transistor M7, so that transistor M10 can generate the replica charging current I by mirroring the current flowing through transistor M7_rchg1. Similarly, using cell reference voltage V_ref2The transistor M11 biases the transistor M8 under the same conditions, so that the transistor M11 can generate the replica cell current I by mirroring the current flowing through the transistor M8_rcell1。

In fig. 2, the bit line bias generator 148 includes an operational amplifier OP3, a transistor M12, and a resistor R1. The operational amplifier OP3 has a positive input terminal for receiving the second bias voltage VB2, a negative input terminal coupled to the first terminal of the transistor M10, and an output terminal for outputting the bit line bias voltage VBLB. The transistor M12 has a first terminal coupled to the output terminal of the operational amplifier OP3, a second terminal coupled to the negative input terminal of the operational amplifier OP3, and a control terminal coupled to the first terminal of the transistor M12. The resistor R1 has a first terminal coupled to the second terminal of the transistor M12 and a second terminal for receiving a second system voltage VS 2.

In this case, when the charging current I is copied_rchg1Greater than replica cell current I_rcell1Time, differential current I_diffWill be fed to the bit line bias generator 148, pulling down the voltage of the negative input terminal of the operational amplifier OP3 and raising the bit line bias voltage VBLB.

In some embodiments, the size ratio of transistors M7 and M10 may be selected to adjust the replica charging current I according to system requirements_rchg1. However, the size ratio of the transistors M8 and M11 should be compared to that of the transistors M7 and M10The size ratio is the same.

Similarly, the size ratio of transistor M6 and voltage bias transistor 110 may be selected according to system requirements, and the size ratio of transistor M6 and voltage bias transistor 110 should be the same as the size ratio of transistor M9 and common source transistor 130.

Further, in fig. 2, the charging current reproduction unit 142 and the cell current reproduction unit 144 may firmly fix the bias condition using the operational amplifiers OP1 and OP 2; however, in some other embodiments, the charging current reproduction unit 142 and the cell current reproduction unit 144 may be implemented with other structures, such as a current mirror in common use.

Also, in fig. 1, the bit lines BL1 through BLN may be precharged at the same time, but in some other embodiments, the bit lines BL1 through BLN may be precharged independently of the page buffers 1201 through 120N according to system requirements.

In summary, the memory system and the bias circuit provided by the embodiment of the invention can immediately adjust the bit line bias voltage according to the charging state of the bit line, so that the strong charging capability can be maintained during the precharge operation. Also, since the charged state of the bit line can be detected by copying the difference between the charge current and the copy cell current, the precharge time can be optimized and the precharge operation can be controlled without being affected by process variations.

Those skilled in the art will readily observe that numerous modifications and alterations of the apparatus and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the scope and metes of the following claims.