Reference voltage generating circuit and internal voltage generating circuit for controlling internal voltage level

Provided are a reference voltage generating circuit and an internal voltage generating circuit for controlling an internal voltage level, where the reference voltage generating circuit includes a distributing unit, a clamping control unit, and a control unit; the distributing unit has a voltage level lower than that of an external power supply voltage in response to the external power supply voltage, and outputs via an output terminal a reference voltage which varies according to an operating mode; the clamping control unit is connected between the output terminal and a ground voltage, and clamps the voltage level of the reference voltage at a constant level in response to a control voltage having a voltage level which is lower than that of the reference voltage; the control unit increases or decreases the voltage level of the reference voltage in response to first and second operating mode signals; the control unit includes a first control transistor and a second control transistor; and the reference voltage generating circuit controls a reference voltage level according to an operating mode of the semiconductor memory device such that the operating characteristics of the semiconductor memory device can be improved in some operating modes and power dissipation can be minimized in other operating modes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims foreign priority under 35 U.S.C. § 119 to Korean Patent Application No. 02-75806 filed on Dec. 2, 2002, in the Korean Intellectual Property Office, and to Korean Patent Application No. 03-64584 filed on Sep. 17, 2003, in the Korean Intellectual Property Office.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor memory devices, and more particularly, to voltage generating circuits of a semiconductor memory device that are responsive to an operating mode.

2. Description of the Related Art

Recent technologies for fabricating semiconductor memory devices have become increasingly hyperfine and highly integrated. Thus, semiconductor memory devices having low power consumption are required. To reduce the power consumption, a power supply voltage to be applied to the semiconductor memory devices may be lowered.

Thus, a conventional semiconductor memory device includes an internal voltage generating circuit for supplying a power supply voltage from an external circuit using a power supply voltage of about 5 V to an internal circuit using a low power supply voltage of about 3.3 V. The internal voltage generating circuit generates an internal voltage in response to a reference voltage received from a reference voltage generating circuit.

In conventional semiconductor memory devices, operating modes are classified according to frequency range. Such operating modes are explained in relation to column address strobe (“CAS”) latency. The CAS latency (“CL”) is a time required for outputting data after a read command is input. That is, when a read command is input at a certain point of a clock signal and then data is output two cycles of the clock signal later, the operating mode is defined for a CAS latency of 2, and becomes, namely, “CL2”.

When a read command is input at a certain point of the clock signal and then data is output three cycles of the clock signal later, the operating mode becomes CL3. Likewise, when a read command is input at a certain point of the clock signal and then data is output two and a half cycles of the clock signal later, the operating mode becomes CL2.5.

If a semiconductor memory device is in the operating frequency range of about 100 to 133 MHz, the device operates in CL2 mode. If a semiconductor memory device is in the operating frequency range of about 166 to 200 MHz, the device operates in CL3 mode.

However, in conventional semiconductor memory devices, an internal voltage is maintained at a constant level regardless of the operating mode, or CL. Thus, when the semiconductor memory device is in an operating mode of a relatively low frequency range, it suffers from unnecessarily increased power dissipation.

Also, even if the internal voltage level of the semiconductor memory device is lowered in order to reduce the power dissipation, operating characteristics may be degraded in an operating mode of a higher frequency range, for example.

Thus, with conventional semiconductor memory devices, if an internal voltage level is controlled in order to improve the operating characteristics of a semiconductor memory device in a certain operating mode, the device may suffer from unnecessarily increased power dissipation in other operating modes.

SUMMARY OF THE INVENTION

The above-described and other drawbacks and disadvantages of the prior art are addressed by a semiconductor memory device that provides a reference voltage generating circuit by which an internal voltage level of the device can be controlled according to an operating mode. Embodiments of the present invention also provide an internal voltage generating circuit by which an internal voltage level of a semiconductor memory device can be controlled according to an operating mode.

In accordance with a first aspect of the present invention, there is provided a reference voltage generating circuit comprising a distributing unit, a clamping control unit, and a control unit.

The distributing unit outputs via an output terminal a reference voltage, which has a voltage level lower than that of an external power supply voltage and varies according to an operating mode, in response to the external power supply voltage.

The clamping control unit is connected between the output terminal and a ground voltage, and clamps a voltage level of the reference voltage at a constant level in response to a control voltage which is lower than the reference voltage.

The control unit increases the voltage level of the reference voltage in response to a first operating mode signal and decreases the voltage level of the reference voltage in response to a second operating mode signal.

The distributing unit includes a first resistor, a second resistor, and first through fourth transistors. The first resistor is connected between the external power supply voltage and the output terminal. The second resistor is connected between the output terminal and a first node from which the control voltage is output.

The first through fourth transistors are connected in series between the first node and the ground voltage. The gates of the first through third transistors are connected to the output terminal, and the external power supply voltage is applied to the gate of the fourth transistor.

The first through fourth transistors are NMOS transistors. The voltage level of the reference voltage is controlled by controlling a width-to-length (“W/L”) ratio of each of the first through fourth transistors.

The control unit includes a first control transistor and a second control transistor. The first control transistor is turned on or turned off in response to the first operating mode signal to increase or decrease the reference voltage level. The second control transistor is turned on or turned off in response to the second operating mode signal to increase or decrease the reference voltage level.

The first control transistor is an NMOS transistor. The source and drain of the NMOS transistor are connected to the source and drain of the first transistor, respectively, and the first operating mode signal is applied to the gate thereof.

The second control transistor is an NMOS transistor. The source and drain of the NMOS transistor are connected to the source and drain of the third transistor, respectively, and the second operating mode signal is applied to the gate thereof.

The clamping control unit is a PMOS transistor. The first and second ends of the PMOS transistor are connected to the output terminal and the ground voltage, respectively, and the control voltage is applied to the gate thereof. The first and second operating mode signals are mode register set (“MRS”) signals.

When the reference voltage generating circuit is in a low operating frequency range, the first and second operating mode signals are at a first level. When the reference voltage generating circuit is in a high operating frequency range, the first and second operating mode signals are at a second level. Also, when the reference voltage generating circuit is in an intermediate operating frequency range, one of the first and second operating mode signals is generated at the first level, and the other is generated at the second level.

In accordance with a second aspect of the present invention, there is provided an internal voltage generating circuit comprising a differential amplifier unit, a distributing unit, and a control unit.

The differential amplifier unit compares a voltage level of a reference voltage with a voltage level of an internal voltage, generates a control signal in response to a comparison result, and controls the voltage level of the internal voltage.

The distributing unit increases or decreases the voltage level of the internal voltage in response to the control signal to clamp the voltage level of the internal voltage at a constant level. The control unit increases the voltage level of the internal voltage in response to a first operating mode signal and decreases the voltage level of the internal voltage in response to a second operating mode signal.

The differential amplifier unit comprises a first transistor having a first terminal connected to an external power supply voltage and having the gate and a second terminal, which are connected to each other; a second transistor having a first terminal connected to the external power supply voltage, the gate connected to the gate of the first transistor, and a second terminal from which the control signal is output; a third transistor having a first terminal connected to the second terminal of the first transistor, the gate connected to the internal voltage, and a second terminal connected to a first node; a fourth transistor having a first terminal connected to the second terminal of the second transistor, the gate connected to the reference voltage, and a second terminal connected to the first node; and a fifth transistor connected between the first node and a ground voltage and having the gate to which a switching signal is applied.

The distributing unit includes first through third distributing transistors. A first terminal of the first distributing transistor is connected to an external power supply voltage, and the control signal is applied to the gate thereof. A first terminal of the second distributing transistor is connected to a second terminal of the first distributing transistor, and the control signal is applied to the gate thereof.

A first terminal of the third distributing transistor is connected to a second terminal of the second distributing transistor, and the control signal is applied to the gate thereof. Also, a second terminal of the third distributing transistor is connected to the internal voltage.

The control unit includes first and second control transistors. The first control transistor is turned on or turned off in response to the first operating mode signal to increase or decrease the internal voltage level. The second control transistor is turned on or turned off in response to the second operating mode signal to increase or decrease the internal voltage level.

In accordance with a third aspect of the present invention, there is provided an internal voltage generating circuit comprising a voltage level detecting unit and a boosting unit.

The voltage level detecting unit determines a voltage level of a first voltage in response to first and second operating mode signals, compares the voltage level of the first voltage with a voltage level of a second voltage, and controls a voltage level of an internal voltage which is higher than a voltage level of an external power supply voltage.

The boosting unit increases or decreases the voltage level of the internal voltage in response to a control signal, which is generated in response to results of a comparison of the voltage level of the first voltage and the voltage level of the second voltage.

The voltage level detecting unit includes a control unit and a differential amplifier unit.

The control unit receives a reference voltage and determines the voltage level of the first voltage in response to the first and second operating mode signals. The differential amplifier unit generates the control signal at a first level when the voltage level of the first voltage is higher than that of the second voltage, and generates the control signal at a second level when the voltage level of the first voltage is lower than the second voltage.

The control unit includes first through fourth resistors, a first control transistor, and a second control transistor. The first through fourth resistors are connected in series between the reference voltage and a ground voltage.

A first terminal of the first control transistor is connected between the first resistor and the second resistor, and the first operating mode signal is applied to the gate thereof. Also, a second terminal of the first control transistor is connected to a first node between the second resistor and the third resistor.

A first terminal of the second control transistor is connected between the third resistor and the fourth resistor, and the second operating mode signal is applied to the gate thereof. Also, a second terminal of the second control transistor is connected between the fourth resistor and the ground voltage.

The first voltage is a voltage level of the first node. The voltage level of the second voltage is proportional to the voltage level of the internal voltage.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The same reference numerals in different drawings represent the same element. Embodiments of the present invention provide a reference voltage generating circuit and an internal voltage generating circuit of a semiconductor memory device for varying an interval voltage level according to an operating mode.

FIG. 1shows a circuit diagram of a reference voltage generating circuit according to a first exemplary embodiment of the present invention.

Referring toFIG. 1, a reference voltage generating circuit100of the present invention comprises a distributor110, a clamping control unit130, and a control unit120.

The distributor110generates, via an output terminal NOUT, a reference voltage VREF, which has a voltage level lower than that of an external power supply voltage EVC, and varies according to an operating mode in response to the external power supply voltage EVC.

More specifically, the distributor110includes a first resistor R1, a second resistor R2, and first through fourth transistors TR1, TR2, TR3, and TR4.

The first resistor R1is connected between the external power supply voltage EVC and the output terminal NOUT. The second resistor R2is connected between the output terminal NOUT and a first node N1from which a control voltage V1is generated.

The first through fourth transistors TR1, TR2, TR3, and TR4are connected in series between the first node N1and a ground voltage. The gates of the first through third transistors TR1, TR2, and TR3are connected to the output terminal NOUT, and the external power supply voltage is applied to the gate of the fourth transistor TR4.

The first through fourth transistors TR1, TR2, TR3, and TR4are NMOS transistors. The voltage level of the reference voltage VREF may be controlled by controlling a width-to-length (“W/L”) ratio of each of the first through fourth transistors TR1, TR2, TR3, and TR4.

The clamping control unit130is connected between the output terminal NOUT and the ground voltage VSS, and clamps the voltage level of the reference voltage VREF at a constant level in response to the control voltage V1, which has a voltage level that is lower than that of the reference voltage VREF.

More specifically, the clamping control unit130is a PMOS transistor. The first and second ends of the PMOS transistor are connected to the output terminal NOUT and the ground voltage VSS, respectively, and the control voltage V1is applied to the gate thereof.

The control unit120increases or decreases the voltage level of the reference voltage VREF in response to the first and second operating mode signals MODE2. The control unit120includes a first control transistor CTR1and a second control transistor CTR2.

The first control transistor CTR1is turned on or turned off in response to the first operating mode signal MODE1to increase or decrease the voltage level of the reference voltage VREF. The second control transistor CTR2is turned on or turned off in response to the second operating mode signal MODE2to increase or decrease the voltage level of the reference voltage VREF.

The first control transistor CTR1is an NMOS transistor. The source and drain of the NMOS transistor are connected to the source and drain of the first transistor TR1and the first operating mode signal MODE1is applied to the gate thereof.

The second control transistor CTR2is an NMOS transistor. The source and drain of the NMOS transistor are connected to the source and drain of the third transistor TR3and the second operating mode signal MODE2is applied to the gate thereof. The first and second operating mode signals MODE1and MODE2are mode register set (“MRS”) signals.

When the reference voltage generating circuit100is in a low operating frequency range, the first and second operating mode signals MODE1and MODE2are at a first level. When the reference voltage generating circuit100is in a high operating frequency range, the first and second operating mode signals MODE1and MODE2are at a second level. Also, when the reference voltage generating circuit100is in an intermediate operating frequency range, one of the first and second operating mode signals MODE1and MODE2is generated at the first level, and the other is generated at the second level.

Hereinafter, operations of the reference voltage generating circuit according to an embodiment of the present invention will be described with reference toFIG. 1.

A distributing unit110generates a reference voltage VREF via an output terminal NOUT in response to an external power supply voltage EVC. The reference voltage VREF has a voltage level lower than that of the external power supply voltage EVC, and varies according to an operating mode.

The distributing unit110comprises a first resistor R1, a second resistor R2, and first to fourth transistors TR1, TR2, TR3, and TR4. The first through fourth transistors TR1, TR2, TR3, and TR4are NMOS transistors.

The first resistor R1is connected between the external power supply voltage EVC and the output terminal NOUT. The second resistor R2is connected between the output terminal NOUT and a first node N1from which a control voltage V1is generated.

The first through fourth transistors TR1, TR2, TR3, and TR4are connected in series between the first node N1and a ground voltage VSS. Thus, current channels are formed in series.

Gates of the first through third transistors TR1, TR2, and TR3are connected to the output terminal NOUT, and the external power supply voltage is applied to the gate of the fourth transistor TR4.

When the external power supply voltage EVC reaches a certain voltage level, the fourth transistor TR4is turned on. Then, a current in the distributing unit110flows from the external power supply voltage EVC connected to the first resistor R1to the ground voltage VSS.

That is, the fourth transistor TR4serves as a switch for operating the distributing unit110.

The first through third transistors TR1, TR2, and TR3are used as resistors. Thus, a voltage is generated at a certain level at the output terminal NOUT based on the voltage divider rule, and is called the reference voltage VREF.

The voltage level of the reference voltage VREF can be controlled by controlling the W/L ratio of each of the first through fourth transistors TR1, TR2, TR3, and TR4.

The clamping control unit130is connected between the output terminal NOUT and the ground voltage VSS, and clamps a voltage level of the reference voltage VREF at a constant level in response to the control voltage V1, which has a lower voltage level than that of the reference voltage VREF. The level of the control voltage V1is controlled by the first through fourth transistors TR1, TR2, TR3, and TR4.

The clamping control unit130is a PMOS transistor. The first and second ends of the PMOS transistor are connected to the output terminal NOUT and the ground voltage VSS, respectively, and the control voltage V1is applied to the gate thereof.

When the external power supply voltage EVC is increased and then maintained at a constant level, the reference voltage VREF is also maintained at a constant level.

A sudden increase in the reference voltage VREF level makes a larger difference between the voltage level of the gate of the clamping control unit130to which the control voltage is applied and the voltage level of the source of the clamping control unit130to which the reference voltage VREF is applied.

Then, the PMOS transistor MP is turned on to a greater extent, and more current flows from the source of the PMOS transistor MP to the drain. As a result, the reference voltage VREF level decreases.

Inversely, a sudden decrease in the reference voltage VREF level makes a smaller difference between the voltage level of the gate of the clamping control unit130to which the control voltage is applied and the voltage level of the source of the clamping control unit130to which the reference voltage VREF is applied.

Then, the PMOS transistor MP is turned on to a smaller extent, and less current flows from the source of the PMOS transistor MP to the drain. As a result, the reference voltage VREF level rises.

As described above, the clamping control unit130is used to maintain the reference voltage VREF at a constant level.

The control unit120increases or decreases the voltage level of the reference voltage VREF in response to the first and second operating mode signal MODE1and MODE2. The control unit120includes a first control transistor CTR1and a second control transistor CTR2.

The first control transistor CTR1is an NMOS transistor. The source and drain of the NMOS transistor are connected to the source and drain of the first transistor TR1, respectively, and the first operating mode signal MODE1is applied to the gate thereof.

The second control transistor CTR2is an NMOS transistor. The source and drain are connected to the source and drain of the third transistor TR3, respectively, and the second operating mode signal MODE2is applied to the gate thereof.

Here, for example, the operating modes of the semiconductor memory device are classified into CL2, CL2.5, and CL3, according to the operating frequency range. Thus, the reference voltage generating circuit100of the exemplary embodiment generates a reference voltage VREF at the lowest level in the CL2 mode, generates a reference voltage VREF at the intermediate level in the CL2.5 mode, and generates a reference voltage VREF at the highest level in the CL3 mode.

In the CL2 mode, the first and second operating mode signals MODE1and MODE2are at a first level. In the CL2.5 mode, one of the first and second operating mode signals MODE1and MODE2is at the first level, and the other is at a second level.

In the CL3 mode, the first and second operating mode signals MODE1and MODE2are at the second level. Here, we suppose for convenience that the first level is a high level and the second level is a low level. However, it will be apparent to those of ordinary skill in the pertinent art that the first level is not limited to the high level and the second level is not limited to the low level.

The first and second operating mode signals MODE1and MODE2are mode register set (“MRS”) signals. If the semiconductor memory device operates in the CL2.5 mode, one of the first and second control transistors CTR1and CTR2is turned on and the other is turned off. Here, for example, the first control transistor CTR1is turned on.

Thus, a current in the distributing unit110flows to the second transistor TR2via the first control transistor CTR1instead of the first transistor TR1. Accordingly, the second resistor R2, the second transistor TR2, the third transistor TR3, and the fourth transistor TR4are used as resistors for determining the voltage level of the reference voltage VREF.

FIG. 2shows a voltage level diagram indicated generally by the reference numeral200. The voltage diagram200illustrates a resulting voltage level VREF_M, for example, of the reference voltage VREF output from the reference voltage generating circuit ofFIG. 1.

If the semiconductor memory device operates in CL2 mode, both the first and second control transistors CTR1and CTR2are turned on. This is because the first and second operating mode signals MODE1and MODE2are both at the high level.

Then, a current in the distributing unit110flows to the second transistor TR2via the first control transistor CTR1instead of the first transistor TR1. Also, a current in the distributing unit110flows to the fourth transistor TR4via the second control transistor CTR2instead of the third transistor TR3.

The second resistor R2, the second transistor TR2, and the fourth transistor TR4are used as resistors for determining a voltage level of the reference voltage VREF. As the number of the resistors for determining the voltage level of the reference voltage VREF is reduced from the case where the semiconductor memory device operates in the CL2.5 mode, the reference voltage VREF level also becomes lower. The resulting level of the reference voltage VREF is indicated by VREF_L of the diagram200.

If the semiconductor memory device operates in CL3 mode, both the first and second control transistors CTR1and CTR2are turned off. This is because the first and second operating mode signals MODE1and MODE2are both at the low level.

Then, a current in the distributing unit110flows to the ground voltage VSS via the first through fourth transistors TR1, TR2, TR3, and TR4. Accordingly, the second resistor R2, and the first through fourth transistors TR1, TR2, TR3, and TR4are used as resistors for determining a voltage level of the reference voltage VREF.

As the number of the resistors for determining the voltage level of the reference voltage VREF is increased from the case where the semiconductor memory device operates in the CL2.5 mode, the reference voltage VREF level also becomes higher. The resulting reference voltage VREF level is indicated by VREF_H of the diagram200.

The internal voltage generating circuit of the semiconductor memory device can control a voltage level of an internal voltage in response to the level of the reference voltage VREF, which varies according to an operating mode.

FIG. 3shows a circuit diagram of an internal voltage generating circuit according to a second embodiment of the present invention.

A differential amplifier unit310compares a voltage level of a reference voltage VREF with a voltage level of an internal voltage IVC, generates a control signal CTRLS in response to a comparison result, and controls the voltage level of the internal voltage IVC.

More specifically, the differential amplifier unit310includes first through fifth transistors TR1, TR2, TR3, TR4, and TR5. A first terminal of the first transistor TR1is connected to an external power supply voltage EVC, and the gate and a second terminal of the first transistor TR1are connected to each other. A first terminal of the second transistor TR2is connected to the external power supply voltage EVC, and the gate of the first transistor TR1is connected to the gate thereof. Also, the control signal CTRLS is output from a second terminal of the second transistor TR2.

A first terminal of the third transistor TR3is connected to the second terminal of the first transistor TR1, and the internal voltage is connected to the gate thereof. A second terminal of the third transistor TR3is connected to a first node N1. A first terminal of the fourth transistor TR4is connected to the second terminal of the second transistor TR2, and the reference voltage VREF is connected to the gate thereof. A second terminal of the fourth transistor TR4is connected to the first node N1.

The fifth transistor TR5is connected between the first node N1and a ground voltage VSS, and a switching signal SW is applied to the gate thereof. To make the differential amplifier unit310operate, the switching signal SW should be input at a high level.

A distributing unit320increases or decreases the voltage level of the internal voltage IVC in response to the control signal CTRLS to clamp the voltage level of the internal voltage IVC at a constant level. The distributing unit320includes first through third distributing transistors DTR1, DTR2, and DTR3.

A first terminal of the first distributing transistor DTR1is connected to the external power supply voltage EVC, and the control signal CTRLS is applied to the gate thereof. A first terminal of the second distributing transistor DTR2is connected to a second terminal of the first distributing transistor DTR1, and the control signal CTRLS is applied to the gate thereof.

A first terminal of the third distributing transistor DTR3is connected to a second terminal of the second distributing transistor DTR2, and the control signal CTRLS is applied to the gate thereof. Also, a second terminal of the third distributing transistor DTR3is connected to the internal voltage IVC.

If the reference voltage VREF is at a higher level than the internal voltage IVC, the differential amplifier unit310outputs the control signal CTRLS at a low level. Then, the first through third distributing transistors DTR1, DTR2, and DTR3are turn on. Accordingly, the internal voltage IVC level increases.

Inversely, if the reference voltage VREF is at a lower level than the internal voltage IVC, the differential amplifier unit310outputs the control signal CTRLS at a high level. Then, the first through third distributing transistors DTR1, DTR2, and DTR3are turn off. Accordingly, the internal voltage IVC level decreases.

The voltage level of the internal voltage IVC is controlled by controlling a width-to-length ratio of each of the first through third distributing transistors DTR1, DTR2, and DTR3.

As described above, the voltage level of the internal voltage IVC may increase or decrease due to the differential amplifier unit310and the distributing unit320.

Also, by using a first operating mode signal MODE1and a second operating mode signal MODE2, the voltage level of the internal voltage IVC can be controlled according to an operating mode.

A control unit330increases or decreases the voltage level of the internal voltage IVC in response to the first and second operating mode signals MODE1and MODE2. The control unit330includes a first control transistor CTR1and a second control transistor CTR2.

The first control transistor CTR1is turned on or turned off in response to the first operating mode signal MODE1to increase or decrease the voltage level of the internal voltage IVC. The second control transistor CTR2is turned on or turned off in response to the second operating mode signal MODE2to increase or decrease the voltage level of the internal voltage IVC.

The first control transistor CTR1is a PMOS transistor. A first terminal and a second terminal of the PMOS transistor are respectively connected to the first terminal and the second terminal of the second distributing transistor DTR2, and the first operating mode signal MODE1is applied to the gate thereof.

The second control transistor CTR2is a PMOS transistor. A first terminal and a second terminal of the PMOS transistor are respectively connected to the first terminal and the second terminal of the third distributing transistor DTR3, and the second operating mode signal MODE2is applied to the gate thereof.

The first and second operating mode signals MODE1and MODE2are mode register set (“MRS”) signals.

We suppose here that the operating modes of the semiconductor memory device are classified into CL2, CL2.5, and CL3, according to the operating frequency range. Here, the internal voltage generating circuit300of the present invention generates an internal voltage IVC at the lowest level in the CL2 mode, generates an internal voltage IVC at the intermediate level in the CL2.5 mode, and generates an internal voltage IVC at the highest level in the CL3 mode.

In the CL2 mode, the first and second operating mode signals MODE1and MODE2are at a first level. In the CL2.5 mode, one of the first and second operating mode signals MODE1and MODE2is at the first level, and the other is at a second level.

In the CL3 mode, the first and second operating mode signals MODE1and MODE2are at the second level. It is supposed for convenience that the first level is a high level and the second level is a low level. However, the first level is not limited to the high level and the second level is not limited to the low level.

That is, if the first and second operating mode signals MODE1and MODE2are at the low level, both the first and second control transistors CTR1and CTR2are turned on. Then, resistance in a current path through the distributing unit320between the external power supply voltage EVC and the internal voltage IVC becomes low.

This is because only the first distributing transistor DTR1is used as a resistor. Accordingly, more current flows in the current path through the distributing unit320and thus the voltage level of the internal voltage IVC increases.

Inversely, in the CL2 mode, if the first and second operating mode signals MODE1and MODE2are at the high level, both the first and second control transistors CTR1and CTR2are turned off. Then, resistance in a current path through the distributing unit320between the external power supply voltage EVC and the internal voltage IVC becomes high.

This is because the first through third distributing transistors DTR1, DTR2, and DTR3are used as resistors. Accordingly, less current flows in the current path through the distributing unit320and thus the voltage level of the internal voltage IVC decreases.

In the CL2.5 mode, if one of the first and second operating mode signals MODE1and MODE2is at the high level and the other is at the low level, one of the first and second control transistors CTR1and CTR2is turned on and the other is turned off.

Then, resistance in a current path through the distributing unit320becomes intermediate between the resistances in the CL2 mode and the CL3 mode. Accordingly, the voltage level of the internal voltage IVC is intermediate between the voltage levels of the internal voltage IVC in the CL2 mode and the CL3 mode.

Since the first and second operating mode signals MODE1and MODE2are controlled according to an operating mode, the internal voltage IVC can be at an appropriate voltage level according to the operating frequency of the semiconductor memory device by controlling the first and second operating mode signals MODE1and MODE2.

Unlike the reference voltage generating circuit100ofFIG. 1, which affects the voltage levels of all internal voltage generating circuits receiving the reference voltage VREF, the internal voltage generating circuit300ofFIG. 3has an advantage of controlling only the voltage level of a required internal voltage generating circuit.

FIG. 4shows a circuit diagram of an internal voltage generating circuit according to yet another embodiment of the present invention.

The internal voltage generating circuit400ofFIG. 4generates an internal voltage IVC, which has a higher voltage level than that of an external power supply voltage EVC. To perform this operation, a voltage level detecting unit410determines a voltage level of a first voltage V1in response to first and second operating mode signals MODE1and MODE2, compares the voltage level of the first voltage V1with a voltage level of a second voltage V2, and controls the voltage level of the internal voltage IVC, which is higher than that of the external power supply voltage.

The voltage level detecting unit410includes a control unit420and a differential amplifier unit430. The control unit420receives a reference voltage VREF and determines the voltage level of the first voltage V1in response to the first and second operating mode signals MODE1and MODE2.

The differential amplifier unit430generates a control signal CTRLS at a first level when the voltage level of the first voltage V1is higher than that of the second voltage V2, and generates the control signal CTRLS at a second level when the voltage level of the first voltage V1is lower than that of the second voltage V2.

The control unit420includes first through fourth resistors R1, R2, R3, and R4, a first control transistor CTR1, and a second control transistor CTR2.

A first terminal of the first control transistor CTR1is connected between the first resistor R1and the second resistor R2, and the first operating mode signal MODE1is applied to the gate thereof. A second terminal of the first control transistor CTR1is connected to a first node N1between the second resistor R2and the third resistor R3.

A first terminal of the second control transistor CTR2is connected between the third resistor R3and the fourth resistor R4, and the second operating mode signal MODE2is applied to the gate thereof. A second terminal of the second control transistor CTR2is connected between the fourth resistor R4and a ground voltage VSS.

The first voltage V1is a voltage level of the first node N1. The voltage level of the first voltage V1is determined by a resistance ratio of the first through fourth resistors R1, R2, R3, and R4. The voltage level of the second voltage V2is proportional to that of the internal voltage IVC.

If the voltage level of the first voltage V1is higher than that of the second voltage V2, since a fourth transistor TR4allows less current to flow than a third transistor TR3, the differential amplifier unit430outputs the control signal CTRLS at a first level. Here, the first level is a high level.

A boosting unit440is turned on in response to the control signal CTRLS having the high level and generates the internal voltage IVC at a higher level than the external power supply voltage EVC.

If the voltage level of the first voltage V1is lower than that of the second voltage V2, since the fourth transistor TR4allows more current to flow than the third transistor TR3, the differential amplifier unit430outputs the control signal CTRLS at a second level. Here, the second level is a low level.

The boosting unit440is turned off in response to the control signal CTRLS having the low level. Then, the internal voltage IVC is maintained at the present voltage level. By these operations, the internal voltage IVC can be maintained at a higher voltage level than the external power supply voltage EVC.

If the level of the internal voltage IVC decreases, the voltage level of the second voltage V2also decreases. Then, the differential amplifier unit430outputs the control signal CTRLS at a high level to increase the voltage level of the internal voltage IVC. On the other hand, if the voltage level of the internal voltage IVC increases, the voltage level of the second voltage V2also increases. Then, the differential amplifier unit430outputs the control signal CTRLS at a low level to turn off the boosting unit440, thereby preventing the voltage level of the internal voltage IVC from increasing.

In the internal voltage generating circuit400, the voltage level of the internal voltage IVC can be controlled according to an operating mode of the semiconductor memory device. That is, the voltage level of the internal voltage IVC increases in a high operating frequency range and decreases in a low operating frequency range.

When the internal voltage generating circuit400is in the high operating frequency range, the first operating mode signal MODE1is at a first level and the second operating mode signal MODE2is at a second level. Here, the second level is a low level and the first level is a high level but the present embodiment is not limited thereto.

The first and second operating mode signals are mode register set (“MRS”) signals. If the first operating mode signal MODE1is at the first level and the second operating mode signal MODE2is at the second level, the voltage level of the first node N1, i.e., the voltage level of the first voltage V1increase.

Thus, the differential amplifier unit430outputs the control signal CTRLS at a high level, and the boosting unit440is turned on to increase the voltage level of the internal voltage IVC. Accordingly, the voltage level of the internal voltage IVC can be increased in the high operating frequency range.

Inversely, when the internal voltage generating circuit400is in a low operating frequency range, the first operating mode signal MODE1is at the second level and the second operating mode signal MODE2is at the first level. Then, the voltage level of the first node N1, i.e., the voltage level of the first voltage V1decrease.

Thus, the differential amplifier unit430outputs the control signal CTRLS at a low level and the boosting unit440is turned off. Accordingly, the voltage level of the internal voltage IVC can be held low in the low operating frequency range.

Since the first and second operating mode signals MODE1and MODE2are controlled according to an operating mode, the internal voltage IVC can be at an appropriate voltage according to the operating frequency of the semiconductor memory device by controlling the first and second operating mode signals MODE1and MODE2.

Also, the internal voltage generating circuit400ofFIG. 4has an advantage of maintaining the internal voltage IVC at a higher level than the external power supply voltage EVC.

As described above, the reference voltage generating circuit and the internal voltage generating circuit of the present invention can control internal voltage level according to the operating mode of the semiconductor memory device. Thus, the operating characteristics of the semiconductor memory device can be improved in some operating modes, while power dissipation can be minimized in other operating modes.