JPH0480480B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor memory device, and particularly to improvements in its sense amplifier.

Common data line pair CDL in static random access memory (RAM),
The sense amplifier that amplifies the signal and transmits it to the data output buffer circuit uses an asymmetric differential amplifier circuit consisting of a differential MISFET and a current mirror circuit (active load) as its load. Therefore, as the output signal, the differential
This sense amplifier can have relatively high sensitivity because it obtains a current that is the difference between the drain currents of the MISFETs. However, since the amplification factor is as small as about 5, a predetermined output voltage cannot be obtained unless the input level difference from the common data line CDL becomes large.

In addition, the offset voltage caused by variations in the characteristics of the elements that make up this sense amplifier is
This sense amplifier has the disadvantage that it is transmitted as is to the next stage. Furthermore, this sense amplifier is an asymmetric type that receives the difference in the level of a pair of input signals as an input signal and forms an output signal having a potential corresponding to the input signal level with respect to the installed potential of the circuit. The noise margin is also reduced due to the influence of logic threshold voltage. From the above, when using the above sense amplifier, it is necessary to increase the level difference between the common data line pair CDL to approximately 0.5 volts.
This is a major obstacle in achieving high-speed operation.

An object of the present invention is to provide a semiconductor memory device that operates at high speed.

Another object of the present invention is to provide a semiconductor memory device equipped with a highly sensitive sense amplifier that reduces variations in device characteristics and the effects of noise.

According to the invention, the common data line pair CDL,
Parallel first and second asymmetric differential amplifier circuits that receive the CDL signal and form output signals with opposite phases to each other are used as sense amplifiers.

Hereinafter, this invention will be explained in detail together with examples.

[Configuration and operation of static memory system]

The configuration of the static memory system will be explained with reference to FIG. First, the block diagram surrounded by dotted lines shows a static memory system, which is an S-RAM IC.
ARRAY (hereinafter referred to as S-RAM) and an interface circuit between the computer's central processing unit (hereinafter referred to as CPU, not shown) and S-RAM. E is a power supply circuit that basically represents the backup function. Normally, the power supply E _O is in operation, but when the power supply E _O is turned off or when it breaks down, the auxiliary power supply E _B is activated. It is configured to hold the memory contents of the memory chip. Note that the power supplies V _CC and V _SS are for all memory ICs.
It has become common to

Next, the static memory system and CPU
The input/output signals between the First, address signals A _p to A _k are signals for selecting addresses of 2 ^k memory cells in the S-RAM surrounded by solid lines. Among them, address signals A _p to A _i are assigned as common address signals to each memory IC, and A ₁₊₁ to _{A k}
The address signal is assigned as a selection signal for the m-column IC array, and is used as a chip select signal common to the ICs in each column. is a write enable signal, which is a data read and write command signal in S-RAM, and all memory ICs
is supplied to the WE terminal of MS is a memory activation signal that starts the memory operation of S-RAM.
D ₁ to _{D 8} are input/output data on a data bus connecting the CPU and S-RAM.

Next, the static memory system is S-RAM.
and the above interface circuit.
First, S-RAM is an nk-bit integrated circuit (hereinafter referred to as nk
It is called. Note that 1k bits indicates 2 ¹⁰ =1024 bits. ) are arranged in m columns and B in rows, and (n
xm) Consists of an IC array connected in a matrix of words x B bits. In addition, IC of line B
The data input terminal D _io and data output terminal D _put of the memory ICs in each row of the array are commonly connected.

Next, the interface circuit will be explained. ADR
is an address receiver that receives address signals A _p to A _k sent from the CPU and converts them into address signals with timing appropriate for the operation of the S-RAM.

DCR is a chip selection control signal (hereinafter referred to as CS ₁ to CS _n) for selecting a chip of the S-RAM.
m=2k ^-1 ).

DBD is a data bus driver in which data input/output between the CPU and S-RAM is switched by a gate control signal GC. Note that the gate control signal GC
are write enable signal and memory activation signal
Created by logical combinations of MS.

The data outputs D _O1 to D _OB of the IC array receive read output signals from the data output terminals of the ICs (B pieces) in the selected column, and the data inputs D _I1 to D _IB of the IC array receive the read output signals from the data output terminals of the ICs (B pieces) in the selected column. Send the write data to the data input terminals D _io (B pieces).

Next, the function of address signals within the static memory system will be explained.

Address signals A _p to A _k from the CPU are divided into two systems, namely, address signals A _p to _{A i} are used as address signals of the memory matrix in each chip of S-RAM, and address signals A _{i+ 1} ~
From the perspective of the S-RAM chip, A _k becomes a chip selection signal indicating whether or not to select the entire chip.

[16k words x 1 bit S-RAM circuit configuration] Figure 2A shows a memory capacity of 16k bits and an output of 1.
BIT's S-RAM integrated circuit (hereinafter referred to as IC)
It shows the internal configuration of.

Each 16k bit memory cell has 128 columns (rows) x 32 rows (columns) = 4096 bits (4k bits)
The memory array is composed of four matrices (memory arrays M-ARY1 to M-ARY4) having a storage capacity of , and each matrix is arranged in two parts on the left and right sides of the row decoder R-DCR.

Row address selection lines (word lines WL1~
WL128, WR1 to WR128) have ²⁸ signals obtained based on the address signals A0 to _A5 , _A12 to _{A13 .}
= 256 decoded output signals are row decoder R
- Sent from DCR.

In this way, the memory M−CEL of each matrix
are word lines WL1 to WL128, WR1 to WR12
8 and one of complementary data line pairs D11, 11 to D132, 132, which will be described later.

Address signals A ₅ and A ₆ are used to select only one of the four memory matrices. Address signal A ₇ to select one column in one selected memory matrix
~A ₁₁ is used.

The memory matrix selection signal GS is decoded into four combinations based on the address signals A ₅ and A ₆ .

Column decoders C- _DCR1 to C- _DCR4 each perform ²⁵ =
Provides 32 different decode output signals for column selection.

During reading, common data line pair CDL,
CDL is the common data line dividing transistor Q ₁ ,
It is divided into four parts for each memory array by Q ₁ ;...;Q ₄ and ₄ , and the common data line pair CDL is commonly coupled at the time of writing.

Sense amplifiers SA1, SA2, SA3, and SA4 are provided corresponding to the divided common data line pairs CDL, respectively.

In this way, the common data line pair CDL is divided, and the sense amplifiers SA1, SA2, SA3, and
The purpose of providing SA4 is to provide common data line pair CDL,
The purpose is to divide the parasitic capacitance of the CDL and speed up the memory cell information read operation.

The address buffer ADB creates 14 pairs of complementary address signals aa ₀ to a ₁₂ from the 14 external address signals A ₀ to A ₁₂ , respectively, and sends them to the decoder circuit (R-
DCR, C-DCR, GS).

The internal control signal generation circuit COM-GE receives two external control signals (chip select signal) and (write enable signal) and generates CS1 (row decoder control signal), SAC (sense amplifier control signal),
Sends we (write control signal), DOC (data output buffer control signal), DIC (data input buffer control signal), etc.

[16k words x 1 bit S-RAM circuit operation] The circuit operation of the S-RAMIC shown in Section 2A will be explained according to the timing diagram of FIG. 2B.

All operations in this IC, that is, address setting operations, read operations, and write operations, are performed only while one of the external control signals is at a low level. At this time, if the other external control signal is at a high level, a read operation is performed, and if the other external control signal is at a low level, a write operation is performed.

First, address setting operation and read operation will be explained.

The address setting operation is always performed based on the address signal applied during this period when the external control signal is at a low level. Conversely, by keeping the external control signal at high level,
Address setting operations and read operations based on uncertain address signals can be prevented.

When the external control signal becomes low level, the row decoder R-DCR receives a high level internal control signal CS1 synchronized with this signal and starts operating. The above row decoder (also word driver) R-
DCR has eight types of complementary pair address signals a ₀ to a ₅ , a
₁₂ to a13 are decoded to select one word line and drive it to high level _.

On the other hand, four memory arrays M-ARY1 to M-
Any one of ARY4 is selected by memory array selection signals m1-m4, and the selected one
one memory array (e.g. M-ARY1)
Two complementary data line pairs (for example, D11, 11) are selected by a column decoder (for example, C-DCR1).

In this way, one memory cell is selected (address set).

The information of the memory cell selected by the address setting operation is sent to one of the divided common data line pairs to the sense amplifier (for example, SA1).
is amplified.

In this case, four sense amplifiers SA1, SA2,
One of SA3 and SA4 is selected by memory array selection signals m1 to m4, and only the selected sense amplifier operates while receiving the high-level internal control signal SAC.

In this way, the four sense amplifiers SA1, SA2,
Power consumption can be reduced by putting three sense amplifiers out of SA3 and SA4 that do not need to be used into a non-operating state. 3 of the above non-operating states
The outputs of the two sense amplifiers are in a high impedance (floating) state.

The output signal of the sense amplifier is the data output buffer.
Amplified by DOB, IC as output data D _put
Sent to the outside.

The data output buffer DOB operates while receiving the high level control signal DOC.

Next, the write operation will be explained.

When the external control signal becomes low level, a high level control signal we synchronized with it is sent to the common data line dividing transistor (Q ₁ , ₁ ;...;
_Q4 , ₄ ) and the common data lines CDL,
CDL is commonly combined.

On the other hand, while receiving the low level control signal DIC, the data input buffer DIB amplifies the input data signal _Dio from outside the IC and sends it to the commonly coupled common data line pair CDL.

The input data signal on the common data line pair CDL is written into the memory cell M-CEL determined by the address setting operation.

[2k words x 8 bits S-RAM circuit configuration] Figure 3A shows a memory capacity of 16k bits and an output of 8 bits.
BIT's S-RAM integrated circuit (hereinafter referred to as IC)
It shows the internal configuration of.

Each 16k bit memory cell has 128 columns (rows) x 16 rows (columns) = 2048 bits (2k bits)
It consists of eight matrices (memory arrays M-ARY1 to M-ARY8) with a storage capacity of
They are arranged separately.

Row address selection lines (word lines WL1~
²⁷ =128 decoder output signals obtained based on address signals _A0 to _A6 are sent from the row decoder R-DCR to WL128, WR1 to WR128).

In this way, the memory M−CEL of each matrix
are word lines WL1 to WL128, WR1 to WR12
8 and one of complementary data line pairs D11, 11 to D132, 132, which will be described later.

Note that the word line intermediate buffers MB1 and MB2 are
Word lines WL1 to WL128, WR1 to each
It has an amplification effect to minimize the delay time at the end of WR128, and M-ARY2 and M-
It is arranged between ARY3 and M-ARY6 and M-ARY7.

Address signals _A7 to _A10 are used to select one column from each of the eight matrices.

Column decoder C-DCR uses the above address signal
Based on A ₇ to _{A 10} , 2 ⁴ =16 decode output signals for column selection are provided.

The address buffer ADB creates 11 pairs of complementary address signals a0 to _a10 from the 11 external address signals _A0 to A10, respectively, and outputs them to the decoder circuits (R-DCR,
C-DCR).

The internal control signal generation circuit COM-GE receives three external control signals (chip select signal), (write enable signal), and (output enable signal), and generates CS1 (row decoder control signal), CS12 (sense amplifier and data input buffer control signal), w・c (write control signal),
Sends w・c・o (data output buffer control signal), etc.

[2k words x 8 bits S-RAM circuit operation] The circuit operation of the S-RAMIC shown in Figure 3A is explained in the third
This will be explained according to the timing diagram shown in Figure B.

All operations in this IC, including address setting operations, read operations, and write operations, are controlled by external control signals.
This is performed only while CS is at low level. At this time, if the other external control signal is at a high level, a read operation is performed, and if the other external control signal is at a low level, a write operation is performed.

The external control signal is used to control the output timing when sending the 8-bit output signal to the outside of the IC.

First, address setting operation and read operation will be explained.

The address setting operation is always performed based on the signal applied during this period when the external control signal is at a low level. Conversely, by keeping the external control signal at a high level, address setting operations and read operations based on uncertain address signals can be prevented.

When the external control signal becomes low level, the row decoder R-DCR receives a high level internal control signal CS1 synchronized with this signal and starts operating. The above row decoder (also word driver) R-
The DCR decodes seven types _of complementary pair address signals a0 _to a6 , selects a pair of left and right word lines, and drives them to a high level.

On the other hand, the column decoder C-DCR selects one column from each of the eight memory arrays M-ARY1 to M-ARY8.

In this way, one memory cell for each memory array, or a total of 8 memory cells, is selected (address setting)
be done.

The information of the memory cell selected by the address setting operation is transmitted to the common data line pair of each memory array.
CDL, and is amplified by each sense amplifier SA.

The sense amplifier SA operates while receiving a high-level control signal CS12 synchronized with an external control signal.

The output signal of the sense amplifier SA is amplified by the data output buffer DOB, and the output data D _put 1~
Sent to the outside of the IC as D _put 8.

The data output buffer DOB operates while receiving the high-level control signals c and o.

Next, the write operation will be explained.

When the external control signals and both become low level, high level control signals w and c synchronized with this are sent to the write control transistors (Q ₁ , ₁ ;
...; _Q4 , ₄ ), and each common data line pair CDL and each data input buffer DIB are coupled.

On the other hand, the data input buffer DIB provided corresponding to each memory array uses a low level control signal.
During the period when CS12 is being received, eight input data signals D _io 1 to _{D io} 8 applied from outside the IC are respectively amplified and sent to the common data line pair CDL provided corresponding to each memory array.

Each input data signal on the common data line pair is written into eight memory cells M-CEL determined by the address setting operation.

[Memory cell circuit]

FIG. 4 shows the circuit of a 1-bit memory cell M-CEL in the memory arrays of FIGS. 2A and 3A. This memory cell is a flip-flop circuit that cross-couples the input and output of a pair of inverter circuits consisting of series-connected load resistors R ₁ and R ₂ and driving MISFETs (insulated gate field effect transistors) Q ₁ and Q ₂ .
For a flop and a pair of transmission gates
It consists of MISFET Q ₃ and Q ₄ . The flip-flop is used as a means of storing information, and the transmission gate connects the flip-flop's complementary data line pair D, (D ₁₁ , ₁₁ . . . D ₁₃₂ , ₁₃₂
The row decoder R is used as an address means to control the transmission of information between
-Word line W (WL1,...) connected to DCR
It is controlled by address signals applied to WL128, WR1, . . . WR128).

[Peripheral circuit]

Figure 5 shows peripheral circuits, such as Figures 2A and 3.
The data output buffer DOB in Figure A is shown. In this data output buffer DOB, when the control signal C _pot is logic "1" (+V _cc ), the output V _put has a logical value according to the input I _o and a very low output impedance is obtained, and C _pot When “0”, V _pot is the input I _o
This results in an undefined level that is not related to the output impedance, that is, a very high output impedance. In this way, a buffer with both high and low output impedances allows wired-OR of multiple buffer outputs.

The final stage uses a bipolar transistor with high drive capacity to drive heavy loads at high speed.
Q ₁₀₅ is used, and Q ₁₀₅ is an N-channel MISFET Q ₁₀₆ which has a larger driving capacity than a P-channel MISFET.
Together with this, they form a push-pull circuit.

Figure 6 shows the static type RAM explained above.
FIG. 2 is a circuit diagram showing an example of a sensor amplifier SA used in the present invention.

In this embodiment, differential MISFETs Q ₂₀₁ and Q ₂₀₂ and active loads MISFETs Q _{203 and 202} that constitute a current mirror circuit are provided at the drains of each.
The first asymmetric differential amplifier circuit consisting of Q ₂₀₄ and
P ₁ and a second asymmetric differential amplifier circuit P ₂ having the same configuration as the above-mentioned asymmetric differential amplifier circuit P ₁ configured by MISFETs Q ₂₀₅ to _{Q 208} , a common data line pair CDL, It receives a signal Di, from and forms output signals D _i ′, _i ′ having mutually opposite phases. That is, the first and second asymmetric differential amplifier circuits P ₁ and P ₂
MISFET Q ₂₀₂ , which is the inverting input terminal (−) of
The above signals D _i and _i are applied to the gate of Q ₂₀₆ , respectively. And it is a non-inverting input terminal (+)
Signals _i and D _i are applied to the gates of MISFETs Q ₂₀₁ and Q ₂₀₅ , respectively, through cross-connections. In this embodiment, a common constant current source is configured for the first and second asymmetric differential amplifier circuits P ₁ and P ₂ .
MISFET Q ₂₀₉ is provided. This MISFET
Replace Q ₂₀₉ with each differential MISFET Q ₂₀₁ ,
A MISFET as a constant current source may be provided in the common source of Q ₂₀₂ , Q ₂₀₅ and Q ₂₀₆ .

In this embodiment, in order to increase the voltage gain in the sense amplifier, the output signals Di, _i ' from the first and second asymmetric differential amplifier circuits P ₁ and P ₂ are
The voltage is applied to a third asymmetric differential amplifier circuit P ₃ having the same configuration as the above-mentioned asymmetric differential amplifier circuits P ₁ and P ₂ configured by MISFETs Q ₂₁₀ to _{Q 214} .

This third asymmetric differential amplifier circuit P ₃
The output signal OUT (D _i ″) from the input/output buffer DOB is transmitted to the input/output terminal IN of the data output buffer DOB shown in FIG.

Also, MISFET Q ₂₀₉ as the constant current source,
In the case of a divided sense amplifier as shown in FIG. 2A, Q ₂₁₄ is a control circuit composed of inverter circuits IV ₁ and IV ₂ and MISFETs Q ₂₁₅ to _{Q 218} that receive the control signal SAC and the memory array selection signal mi. circuit
Switch controlled by CONT.

On the other hand, in the case of a sense amplifier that is not divided into corresponding data output buffers as in the embodiment shown in FIG. 3A, the signal CS as shown in FIG. 3B is
12 is applied to the gates of MISFETs Q ₂₀₉ and Q ₂₁₄ as the constant current sources.

According to this embodiment, two asymmetric differential amplifier circuits P ₁ and P ₂ are used to form balanced signals D _i ′ and _i ′. Therefore, even if the asymmetric differential amplifier circuits P ₁ and P ₂ have offset voltages, if they are formed in the same monolithic IC, the offset voltages will be generated in the same way, so both can be used together. It can be offset.

Furthermore, even if nozzles that are in phase with the input signals D _i and _i appear, these can be canceled out.

Furthermore, in order to increase the amplification factor, a similar asymmetric differential amplifier circuit _P3 can be provided at the next stage.
Note that the offset voltage of this asymmetric differential amplifier circuit _P3 is transmitted to the next stage, but the above signal
Since the signal levels of D _i ′ and _i ′ are large, they can be virtually ignored.

This makes it possible to reduce the effects of offset voltage and noise, and to obtain a sense amplifier with high sensitivity and high amplification factor.

Incidentally, even if the voltage difference between the signals D _i and _i from the common data line pair CDL is as small as about 0.2 volts, the sense amplifier SA of this embodiment can generate an output signal sufficient to drive the data output buffer DOB.
can be formed, and high-speed operation of static RAM can be achieved.

In the embodiment circuit of FIG. 6, the third asymmetric differential amplifier circuit P ₃ is omitted, and the signals D _i ′,
D _i ' may be transmitted to the next stage data output buffer DOB. In this case, in the data output buffer DOB of FIG. 5, the inverter circuit _G102 is omitted, and the signals D _i ', _i ' are directly input to the terminals T ₁ , T ₂ .

In this case, by using the balanced signals D _i ′, _i ′ as the output signals, the amplification factor can be doubled compared to the case where one asymmetric differential amplifier circuit is used as described above. . Then, as described above, offset voltage and common mode noise can be canceled out.

FIG. 7 shows a block diagram of another embodiment of the invention.

In this embodiment, balanced signals D _i ′, _i ′ are formed by asymmetric differential amplifier circuits P ₁ , P ₂ similar to those described above. And a similar asymmetric differential amplifier circuit P ₄ ,
_P5 is provided to form a balanced output signal OUT. Each asymmetric differential amplifier circuit P ₁ , P ₂
The specific circuits of P ₄ and P ₅ are the same as the circuit shown in FIG. 6, so their explanation will be omitted.

The above balanced output signal OUT, in the data output buffer DOB of Fig. 5, is the inverter circuit.
G ₁₀₃ is omitted, and the signals are directly input to one input terminals T ₁ and T ₂ of gate circuits G ₁₀₁ and G ₁₀₂ , respectively. In this embodiment, since the output signal is also a balanced signal, the output side asymmetric differential amplifier circuits P ₄ , P ₅
It is also possible to cancel out the offset voltage of the Also, the amplification factor is also lower than that of the example circuit shown in Fig. 6.
It can be made twice as large.

This makes it possible to more easily reduce the effects of offset voltage and noise, and to obtain sense-up with high sensitivity and high amplification factor.

FIG. 8 is a circuit diagram showing another specific embodiment of the asymmetric differential amplifier circuit P.

This example uses MISFET Q ₂₂₁ whose gate is grounded as a load for differential MISFET Q ₂₁₉ and Q ₂₂₀ .
, and MISFET Q ₂₂₂ with the common drain of these MISFETs _{Q 219} and Q ₂₂₁ connected to the gate. In this embodiment, since the voltage between the source and gate of the load MISFET Q ₂₂₂ can be increased, a higher amplification factor can be obtained than in the case of using a current mirror circuit, but on the other hand, the offset voltage is increased. However, when used in configurations such as the asymmetric differential amplifier circuits P ₁ , P ₂ and P ₄ , P ₅ in Figures 6 and 7, this becomes a problem because the offset voltages can be canceled out. There is no problem, and the high amplification factor is utilized.

Figure 9 shows the asymmetric amplifier circuit of Figures 6 and 7.
A layout diagram is shown in which P ₁ and P ₂ are formed on a monolithic IC.

In the same figure, the thick solid lines indicate aluminum wiring, power supply voltage Vc.c., ground GND line, and differential MISFET Q ₂₀₁ , Q ₂₀₂ , Q ₂₀₅ , Q ₂₀₆
common source connection, differential MISFET and load
Used for common drain connection with MISFET.

The thin solid line indicates a conductive polysilicon layer, which is used for the gate electrode of each MISFET and its associated wiring.

The dashed line indicates a p-type or n-type diffusion region,
Source or drain of MISFET and differential
Used for MISFET gate cross-connection.

The dashed line indicates a p-type well region formed on the n-type substrate. Therefore, an n-channel MISFET is formed within this P-well. Further, □× marks indicate contacts.

The invention is not limited to the above embodiments.

The system configuration of the static RAM can take various embodiments.

[Brief explanation of the drawing]

1 to 9 all show one embodiment of the present invention, in which FIG. 1 is a block diagram of a static memory system, FIG. 2A is a block diagram of the internal configuration of S-RAMIC, and FIG. 2B is a block diagram of an internal configuration of an S-RAMIC. is a timing diagram thereof, and FIG. 3A is an S-
The internal configuration block diagram of RAMIC, Figure 3B is its timing diagram, and Figure 4 is the one in the memory array.
5 is a circuit diagram of a data output buffer, FIG. 6 is a circuit diagram of a sense amplifier, and FIG. 7 is a block diagram of a sense amplifier showing another embodiment. FIG. 8 is a circuit diagram of an asymmetric differential amplifier circuit showing another embodiment used in the sense amplifier, and FIG. 9 is a layout diagram of the main parts of the sense amplifier.

Claims (1)

[Scope of Claims] 1. A sense amplifier that receives a signal from a data line pair and outputs output signals having opposite phases to each other, which are amplified with respect to the signal, to first and second connection points;
A semiconductor memory device comprising: an output buffer having an output transistor that is push-pull driven based on output signals of mutually opposite phases from a second connection point, wherein the sense amplifier receives signals from the data line pair. a first differential amplifier circuit that receives a signal from the data line pair at its pair of inputs and forms an output signal of one phase by receiving the signal from the pair of data lines at its pair of inputs, and generates a signal of opposite phase to the output signal. A second differential amplifier circuit to be formed receives the mutually opposite output signals of the first and second differential amplifier circuits at its pair of inputs, and outputs mutually opposite phase output signals to the first and second differential amplifier circuits. The first to fourth differential amplifier circuits each include a pair of differential input elements and one input element of the differential amplifier elements. A semiconductor memory device comprising: an asymmetrical load means that generates a current in response to a current and generates an output according to a difference between the current of the differential input element and the current of the other input element. 2 The differential input element is a first conductivity type differential input element.
MISFET, and the asymmetric load means receives the drain current of one MISFET of the differential MISFETs as an input, and forms an output current to be combined with the drain current of the other MISFET of the differential MISFETs. 2. The semiconductor device according to claim 1, comprising a load circuit. 3. The output buffer includes a gate circuit that receives output signals of mutually opposite phases and an output control signal supplied via the first and second connection points,
3. The semiconductor memory device according to claim 1, wherein the semiconductor memory device is configured to take a signal output state and an output high impedance state depending on the output control signal. 4. The first to fourth differential amplifier circuits are connected in series with a current source controlled by a control signal conditioned on a chip select signal, so that the operating current is controlled. A semiconductor memory device according to any one of claims 1 to 3.