Input circuit for semiconductor integrated circuit

1. Technical Field

The present invention relates to a semiconductor integrated circuit, and more particularly, to an input circuit that receives a signal from the outside and transmits the received signal to an internal circuit.

2. Related Art

A semiconductor integrated circuit includes a signal transmitting unit that receives a signal and transmits it, and a signal processing unit that processes the signal transmitted by the signal transmitting unit according to a predetermined operation. The signal processing unit is generally called a core circuit of the semiconductor integrated circuit. In this core circuit, a large number of elements are integrated within an allowable range of design and process technologies of the semiconductor integrated circuit. The signal transmitting unit includes an input circuit and an output circuit disposed therein. The input circuit transmits a signal transmitted from the outside to the signal processing unit inside the semiconductor integrated circuit, and the output circuit outputs data transmitted by the signal processing unit to the outside.

Among semiconductor integrated circuits, in the case of a semiconductor memory, an input circuit mainly receives an address signal or data so as to transmit it to a memory core region inside the semiconductor memory, and an output circuit outputs a data signal corresponding to an input address to the outside of the memory.

As such, the input circuit receives a data signal or an address signal transmitted from outside of the input circuit and transmits it to an inner part of the semiconductor integrated circuit. The input circuit needs to perform an accurate buffering operation such that the semiconductor integrated circuit operates reliable.

FIG. 1 is a circuit diagram illustrating an input circuit for a semiconductor integrated circuit according to the related art. The input circuit according to the related art is generally implemented by a differential amplifier.

Referring to FIG. 1 , the input circuit for a semiconductor integrated circuit according to the related art includes a MOS transistor Q 1 that receives a reference voltage vref, a MOS transistor Q 2 that receives an input signal in from the outside, two MOS transistors Q 3 and Q 4 that form a current mirror, two MOS transistors Q 5 and Q 6 for pull up that are enabled or disabled according to an enable signal enable, and a MOS transistor Q 7 that receives the enable signal enable and drives differential amplifying operations of the two MOS transistors Q 1 and Q 2 . The input circuit for a semiconductor integrated circuit further includes, as an output terminal, an inverter I 1 that inverts a signal provided by a common node between the MOS transistors Q 2 and Q 4 and outputs an output signal out. Also, the input circuit of FIG. 1 uses a power supply voltage vdd and a ground voltage VSS as source voltages. The MOS transistors Q 1 and Q 2 operate as input transistors, the MOS transistors Q 3 , Q 4 , Q 5 , and Q 6 operate as pull-up transistors, the MOS transistor Q 7 operates as a driving transistor, and the inverter I 1 operates as an output driver.

First, if the enable signal enable is input in a state where the enable signal enable is activated, that is, the enable signal enable becomes a high level, the MOS transistors Q 5 and Q 6 become disabled, and the MOS transistor Q 7 becomes enabled, which provides a bias current of the MOS transistors Q 1 and Q 2 .

The reference voltage vref is inputted to the MOS transistor Q 1 in a state where it is maintained at a predetermined level. Meanwhile, if the input signal in is inputted to the MOS transistor Q 2 , the difference between the signals that are supplied from the MOS transistors Q 3 and Q 4 forming a current mirror to the two MOS transistors Q 1 and Q 2 is generated, due to the difference between the input signal in and the reference voltage vref. At this time, a signal that corresponds to the difference between the signals is transmitted to the input of the inverter I 1 . The inverter I 1 inverts the input signal according to the size of the signal transmitted to the input of the inverter I 1 , and outputs an output signal out. For example, when the input signal in is inputted at a signal level higher than the reference voltage vref, a turned-on period of the MOS transistor Q 2 is longer than that of the MOS transistor Q 1 , and a large amount of current flows through the MOS transistor Q 2 . As a result, the inverter I 1 generates an output signal of a high level. In contrast, when the input signal in is inputted at a signal level lower than the reference voltage vref, the turned-on period of the MOS transistor Q 2 is shorter than that of the MOS transistor Q 1 , and a small amount of current flows through the MOS transistor Q 2 . As a result, the inverter I 1 generates an output signal of a low level.

Meanwhile, during a manufacturing process of the semiconductor integrated circuit, as a MOS transistor is manufactured according to process conditions, characteristics of the MOS transistor gradually varies. Also, a voltage level of the power supply voltage vdd can vary gradually with respect to the environment where the semiconductor integrated circuit operates. The operational characteristics of the MOS transistor that forms the input circuit also varies gradually according to an ambient temperature at the time of operation.

That is, the operational characteristics of all MOS transistors that form an input circuit also vary due to the variation in PVT (process, voltage, and temperature). As a result, even when a duty ratio of the input signal in inputted to the input circuit is constant, it varies while passing through the input circuit, and a duty ratio is distorted in an output signal out of the input circuit.

The input circuit is designed to have a structure in which even when an input signal input having a predetermined duty ratio becomes an output signal, the input signal is outputted with the predetermined duty ratio. However, as described above, the operational characteristic of the input circuit continuously varies according to the PVT, and when the input signal becomes the output signal out, the duty ratio is distorted. When the duty ratio is distorted, a margin of a setup/hold time is also reduced.

The setup/hold time refers to a margin in which the semiconductor integrated circuit can receive a desired signal according to a timing of a rising edge or a falling edge of a clock signal. When the duty ratio is distorted, the margin of the setup/hold time is reduced, and signals to be inputted to the semiconductor integrated circuit may not be securely inputted, which causes an erroneous operation.

Embodiments of the present invention provide an input circuit for a semiconductor integrated circuit that is capable of maintaining a stable operation even when process conditions, a temperature, and a voltage vary.

Another embodiment of the invention provides an input circuit for a semiconductor integrated circuit that is capable of surely coping with the variation in ambient environment conditions, and maintaining a constant operation.

Still another embodiment of the invention provides an input circuit for a semiconductor integrated circuit that is capable of reducing an influence due to the variation in process conditions, a temperature, and a voltage, and increasing a setup/hold time.

A first embodiment of the invention provides an input circuit for a semiconductor integrated circuit, which includes a first input unit that performs a first amplifying operation on a potential difference between a reference voltage and an input signal and outputs a result of the amplification, and a second input unit that performs a second amplifying operation on a signal amplified by the first input unit and outputs a result of the amplification.

A second embodiment of the invention provides an input circuit for a semiconductor integrated circuit, which includes a first input unit that is biased by a bias signal, and performs a first amplifying operation on a potential difference between a reference voltage and an input signal and outputs a result of the amplification, a second input unit that performs a second amplifying operation on a signal amplified by the first input unit and outputs a result of the amplification, a first bias signal providing unit that amplifies the reference voltage to a predetermined level on the basis of an operational state biased by the bias signal, and outputs a result of the amplification, and a second bias signal providing unit that compares a signal provided by the first bias signal providing unit and an internal reference voltage, amplifies a difference value, and generates the bias signal.

A third embodiment of the invention provides an input circuit for a semiconductor integrated circuit, which includes a first input unit that performs a first amplifying operation on a potential difference between a reference voltage and an input signal and outputs a result of the amplification, a second input unit that performs a second amplifying operation on a signal amplified by the first input unit and outputs a result of the amplification, and a bias signal proving unit that provides a bias signal such that the first input unit is driven by the bias signal. Preferably, the first input unit includes a differential amplifier that uses resistors as loads. Preferably, the second input unit includes a differential amplifier that uses MOS transistors as loads. Preferably, the bias signal providing unit includes a first bias signal providing unit that amplifies the reference voltage to a predetermined level on the basis of an operational state biased by the bias signal and outputs a result of the amplification, and a second bias signal providing unit that compares a signal outputted by the first bias signal providing unit and an internal reference voltage, amplifies a difference value, and generates the bias signal. Preferably, the second bias signal providing unit includes a resistance divider that outputs the internal reference voltage.

According to embodiments of the invention, the input circuit for a semiconductor integrated circuit is constructed in two stages. The input circuit receives the reference voltage and the input signal, performs an amplifying operation thereon, performs an amplifying operation on the amplified signal again as an input signal, and transmits it to an inner region. A first stage uses a resistor as a constant current source, an increases a swing width of a signal inputted to a second stage, and increases a voltage gain. When the voltage gain is increased, a distortion in a duty ratio can be reduced even when the variation in PVT occurs.

Further, even when an operational state of the first stage of the input circuit using the resistor varies due to the variation in PVT, the bias signal that is fed back by the same amplifier as the first stage is used in bias signal providing of the first stage, and the signal that is inputted to the second stage of the input circuit is adjusted. As a result, the duty ratio can be maintained to a predetermined value.

FIG. 1 is a circuit diagram illustrating an input circuit for a semiconductor integrated circuit according to the related art;

FIG. 2 is a circuit diagram illustrating an input circuit for a semiconductor integrated circuit according to an embodiment of the present invention;

FIG. 3 is a circuit diagram illustrating a bias signal providing unit that provides a bias signal to an input circuit shown in FIG. 2 ;

FIG. 4 is a circuit diagram illustrating an input circuit for a semiconductor integrated circuit according to another embodiment of the present invention; and

FIG. 5 is a circuit diagram illustrating an input circuit for a semiconductor integrated circuit according to still another embodiment of the invention.

Embodiments of the invention will now be described in detail with reference to the accompanying drawings.

Referring to FIG. 2 , an input circuit 100 of a semiconductor integrated circuit according to an embodiment of the invention includes a first input unit 110 that performs a first amplifying operation on the difference between a reference voltage vref and an input signal in and outputs a result of the amplification; and a second input unit 120 that performs a second amplifying operation on the signal amplified by the first input unit 110 and outputs a result of the amplification.

The first input unit 110 includes a differential amplifier that uses resistors R 1 and R 2 as loads. The second input unit 120 includes a differential amplifier that uses MOS transistors T 7 and T 8 as loads.

The first input unit 110 includes the first resistor R 1 , the second resistor R 2 , and first to fourth MOS transistors T 1 to T 4 . One end of each of the first and second resistors R 1 and R 2 is connected to a power supply voltage supply terminal vdd. The first MOS transistor T 1 is connected to the first resistor R 1 , and is driven in response to the input signal in. The second MOS transistor T 2 is connected to the second resistor R 2 and operates in response to the reference voltage vref. The third MOS transistor T 3 is connected in common to the first and second MOS transistors and is driven in response to an enable signal enable. The fourth MOS transistor T 4 is connected to the third MOS transistor T 3 and is driven in response to a bias signal bias. The other end (for example, source) of the fourth MOS transistor T 4 is connected to a ground voltage supply terminal VSS. In the above-described structure, each of the first to fourth MOS transistors T 1 , T 2 , T 3 , and T 4 is composed of an NMOS transistor. Further, the MOS transistors T 1 and T 2 operate as input transistors, and the resistors R 1 and R 2 operate as pull-up loads, and the MOS transistors T 3 and T 4 operate as driving transistors. Through this structure, a first output signal oin of the first input unit is outputted through a node to which the input transistor T 1 is connected, and a second output signal oref of the first input unit is outputted through a node to which the input transistor T 2 is connected.

The second input unit 120 includes fifth to eleventh MOS transistors T 5 to T 11 . The fifth MOS transistor T 5 has a gate that receives a signal applied to a common node between the second resistor R 2 and the second MOS transistor T 2 . The sixth MOS transistor T 6 has a gate that receives a signal applied to a common node between the first resistor R 1 and the first MOS transistor T 1 . One end (i.e., source) of the seventh MOS transistor T 7 is connected to the power supply voltage supply terminal vdd, and the other end (i.e., drain) thereof is connected to the fifth MOS transistor T 5 . One end (i.e., source) of the eighth MOS transistor T 8 is connected to the power supply voltage supply terminal vdd, and the other end (i.e., drain) thereof is connected to one end of the sixth MOS transistor T 6 . A gate of the seventh MOS transistor T 7 is connected to a gate of the eighth MOS transistor T 8 . Further, the gate of the seventh MOS transistor T 7 is electrically connected to the other end (for example, drain) thereof. The ninth MOS transistor T 9 has one end (i.e., drain) connected in common to the other ends (i.e., source) of the fifth and sixth MOS transistors T 5 and T 6 , the other end (i.e., source) connected to the ground voltage supply terminal VSS, and a gate receiving an enable signal enable. The tenth MOS transistor T 10 is disposed between the power supply voltage supply terminal vdd and one end of the seventh MOS transistor T 7 , and has a gate that receives the enable signal enable. The eleventh MOS transistor T 11 is disposed between the power supply voltage supply terminal vdd and one end of the eighth MOS transistor T 8 , and has a gate that receives the enable signal enable. In the above-described structure, each of the fifth, sixth, and ninth MOS transistors T 5 , T 6 , and T 9 may be composed of an NMOS transistor, and each of the seventh, eighth, tenth, and eleventh MOS transistors T 7 , T 8 , T 10 , and T 11 may be composed of a PMOS transistor. Further, in the above-described structure, the MOS transistors T 5 and T 6 operate as input transistors, and the seventh, eighth, tenth, and eleventh MOS transistors T 7 , T 8 , T 10 , and T 11 operate as pull-up transistors, and the ninth transistor T 9 operates as a driving transistor. Through this structure, a differential amplifying signal diff_out is outputted through a node to which the input transistor T 6 is connected, and a final output signal outb is outputted through an inverter I 2 .

FIG. 3 is a circuit diagram illustrating a bias signal providing unit that provides a bias signal bias to the input circuit shown in FIG. 2 .

Referring to FIG. 3 , the bias signal providing unit 200 includes a first bias signal providing unit 210 and a second bias signal providing unit 220 .

The first bias signal providing unit 210 amplifies the reference voltage vref to a predetermined level on the basis of an operational state biased by the bias signal bias and outputs it. The first bias signal providing unit 210 includes a third resistor R 3 , a fourth resistor R 4 , and twelfth to fifteenth MOS transistors T 12 to T 15 . One end of each of the third and fourth resistors R 3 and R 4 is connected to the power supply voltage supply terminal vdd. Specifically, the first bias signal proving unit 210 includes the third resistor R 3 , the fourth resistor R 4 whose one end is connected to the power supply voltage supply terminal vdd, the twelfth MOS transistor T 12 that has one end connected to the other end of the third resistor R 3 , and a gate supplied with the reference voltage vref, the thirteenth MOS transistor T 13 that has one end connected to the other end of the fourth resistor R 4 , and a gate supplied with the reference voltage vref, the fourteenth MOS transistor T 14 that has one end connected commonly to the other ends of the twelfth and thirteenth MOS transistors T 12 and T 13 and a gate connected to the power supply voltage supply terminal vdd, and the fifteenth MOS transistor T 15 that has one end connected to the other end of the fourteenth MOS transistor T 14 , a gate receiving a bias signal bias, and the other end connected to the ground voltage supply terminal VSS. In the above-described structure, each of the twelfth to fifteenth MOS transistors T 12 , T 13 , T 14 , and T 15 is composed of an NMOS transistor. In the above-described structure, the MOS transistors T 12 and T 13 operate as input transistors, the resistors R 3 and R 4 operate as pull-up loads, and the MOS transistors T 14 and T 15 operate as driving transistors. Through this structure, an output signal refc of the first bias providing unit is outputted through a common node to which the input transistors T 12 and T 13 are connected.

The second bias signal providing unit 220 compares a signal provided by the first bias signal providing unit 210 with an internal reference voltage iverf, and amplifies the signal according to the comparison result to generate a bias signal bias. The second bias signal providing unit 220 includes the fifth resistor R 5 , the sixth resistor R 6 , and the sixteenth to twentieth MOS transistors T 16 to T 20 . Specifically, the fifth and sixth resistors R 5 and R 6 are connected in series between the power supply voltage supply terminal vdd and the ground voltage supply terminal VSS, and output an internal reference voltage ivref that is divided. The sixteenth MOS transistor T 16 has a gate that receives the output signal refc of the first bias signal providing unit, and the seventeenth MOS transistor T 17 has a gate that is supplied with the internal reference voltage ivref. The eighteenth MOS transistor T 18 has an end connected to the power supply voltage supply terminal vdd, the other end connected to one end of the sixteenth MOS transistor T 16 , and a gate connected to a gate of the nineteenth MOS transistor T 19 located at an opposite side. The nineteenth MOS transistor T 19 has one end (i.e., source) connected to the power supply voltage supply terminal vdd, the other end (i.e., drain) connected to one end (i.e., drain) of the seventeenth MOS transistor T 17 , and a gate connected to the gate of the seventeenth MOS transistor T 17 . The twentieth MOS transistor T 20 has one end (i.e., drain) connected in common to the other ends (i.e., drain) of the sixteenth and seventeenth MOS transistors T 16 and T 17 , the other end (i.e., source) connected to the ground voltage supply terminal VSS, and a gate supplied with the internal reference voltage ivref. In the above-described structure, each of the sixteenth, seventeenth, and twentieth MOS transistors T 16 , T 17 , and T 20 is composed of an NMOS transistor, and each of the eighteenth and nineteenth MOS transistors T 18 and T 19 is composed of a PMOS transistor. In the above-described structure, the MOS transistors T 16 and T 17 operate as input transistors, the eighteenth and nineteenth MOS transistors T 18 and T 19 operate as pull-up transistors, and the twentieth MOS transistor T 20 operates as a driving transistor. Through this structure, the bias signal bias is outputted through a node to which the input transistor T 17 is connected.

The operation of the input circuit for a semiconductor integrated circuit according to an embodiment of the invention will now be described with reference to FIGS. 2 and 3 .

As shown in FIG. 2 , the input circuit according to an embodiment of the invention includes two stages. When the enable signal enable is at a low level, voltage levels of the signals oin, oref, and dif_out at the nodes become a power supply voltage (vdd) level. As a result, the first input unit 110 and the second input unit 120 become disabled.

When the enable signal enable becomes a high level, the first input unit 110 becomes enabled. Further, a bias state of the first input terminal 110 is determined by the bias signal bias inputted to the gate of the fourth MOS transistor T 4 . The first input unit 110 outputs the result that is obtained by amplifying the difference between the reference voltage vref and the input signal in as two signals inputted to the first input unit 110 by a predetermined voltage gain.

The second input unit 120 also becomes enabled according to the enable signal enable, and outputs the result that is obtained by amplifying a voltage difference between two signals oin and oref supplied from the output nodes of the first input unit 110 by a predetermined voltage gain.

The input circuit according to an embodiment of the present invention includes the two input units, each of which performs an amplifying operation, and transmits the signal inputted to an inner part of the semiconductor integrated circuit by performing an amplifying operation twice. Accordingly, an amplified voltage gain in the input signal inputted to the input circuit is increased as compared with the related art, which reduces signal distortion due to the PVT.

Specifically, even when the second input unit 120 performs a distorted operation due to the PVT, the second input unit 120 again performs an amplifying operation on the signal that has been amplified by the first input unit 110 , which reduces a signal distortion.

Meanwhile, the signal amplified by the first input unit 110 may be varied due to the PVT. The signal that has been distorted by the first input unit 110 may be further distorted by the second input unit 120 .

However, if a biasing operation is performed at the first input terminal 110 using the bias signal bias provided by the first and second bias signal providing units 210 and 220 , even when the characteristics of the first input unit 110 vary due to the PVT, that is, the characteristics between a resistor and a transistor in the first input unit 110 are distorted, the signals oin and oref the output nodes may be constant by means of the bias voltage.

As shown in FIG. 3 , the first and second bias signal providing units 210 and 220 have structures similar to those of the first input unit 110 and the second input unit 120 shown in FIG. 2 , and operate using a differential amplifying operation.

The first bias signal providing unit 210 is supplied with the reference voltages vref as the two input signals and outputs the output signal refc of the first bias signal providing unit, and the second bias signal providing unit 220 at a next stage receives the output signal refc of the first bias signal providing unit, compares a potential of the output signal refc of the first bias signal providing unit and a potential of an internal reference voltage ivref generated by a resistance divider in the second bias signal providing unit 220 , and generates a bias signal bias. The bias signal bias that is generated in the above-described manner is fed back to the first bias signal providing unit 210 , and adjusts the generation of the output signal refc of the first bias signal providing unit. The output signal refc of the first bias signal providing unit that is generated by using the signal fed back to the first bias signal providing unit 210 contributes to generate the bias signal bias again, and forms a loop.

Even when the characteristics between the resistor and the transistor in the first input unit 110 vary due to the variation in the PTV, the bias voltage, which is generated by the first bias signal generating unit 210 to which the same structure and characteristic as the first input unit 110 are applied, is adjusted. Accordingly, the output signals oin and oref that are outputted from the output nodes of the first input unit 110 can be maintained at a predetermined level without being influenced by the variation in the PVT.

FIG. 4 is a diagram illustrating a structure of an input circuit for a semiconductor integrated circuit according to another embodiment of the invention.

Similar to the input circuit for the semiconductor integrated circuit according to the first described embodiment of the invention, an input circuit 300 according to another embodiment of the invention includes a first input unit 310 that performs a first amplifying operation on a potential difference between a reference voltage vref and an input signal in, and a second input unit 320 that receives the signal amplified by the first input unit 310 , compensates for a variation in the reference voltage Vref, and performs a second amplifying operation on the signal amplified by the first input unit 310 .

The first input unit 310 according to this embodiment has the same structure as the first input unit 110 according to the above-described embodiment, except that a third resistor R 3 is connected, instead of the fourth transistor T 4 according to the above-described embodiment. Further, in order to discriminate between the above-described embodiment and the currently described embodiment, a transistor is denoted by reference character “TR”.

The second input unit 320 includes a pull-up unit 322 , a pull-up compensating unit 324 , a pull-down unit 326 , and a pull-down compensating unit 328 .

The pull-up unit 322 operates in accordance with an enable signal enable, and supplies an external power supply voltage VDD to a first node N 1 and an output node Nout according to a potential level at the first node N 1 . The pull-up unit 322 includes a fifth transistor TR 5 that has one end (i.e., source) connected to a terminal of the external power supply voltage VDD, the other end (i.e., drain), and a gate commonly connected to the first node N 1 , a sixth transistor TR 6 that has one end (i.e., source) connected to the terminal of the external power supply voltage VDD, the other end (i.e., drain) connected to the output node Nout, and a gate connected to the first node N 1 , and a seventh transistor TR 7 that has one end connected to the terminal of the external power supply voltage VDD, the other end connected to the output node Nout, and a gate receiving the enable signal enable.

The pull-up compensating unit 324 compensates for a pull-up operation on the first node N 1 and the output node Nout of the pull-up unit 322 according to a variation in the reference voltage Vref. The pull-up compensating unit 324 includes an eighth transistor TR 8 that has one end (i.e., source) connected to the terminal of the external power supply voltage VDD, the other end (i.e., drain) connected to the first node N 1 , and a gate receiving the reference voltage Vref.

The pull-down unit 326 operates in accordance with the enable signal enable, and supplies a ground voltage VSS to the first node N 1 and the output node Nout in response to a first output signal oin and a second output signal oref. The pull-down unit 326 includes a ninth transistor TR 9 that has one end (i.e., drain) connected to the first node N 1 , the other end (i.e., source) connected to the second node N 2 , and a gate receiving the second output signal oref, a tenth transistor TR 10 that has one end (i.e., drain) connected to the output node Nout, the other end (i.e., source) connected to the second node N 2 , and a gate receiving the first output signal oin, and an eleventh transistor TR 11 that has one end (i.e., drain) connected to the second node N 2 , the other end (i.e., source) connected to a ground terminal, and a gate receiving the enable signal enable.

The pull-down compensating unit 328 compensates for a pull-down operation on the first node N 1 and the output node Nout of the pull-down unit 326 according to the variation in the reference voltage Vref. The pull-down compensating unit 328 includes a twelfth transistor TR 12 that has one end (i.e., drain) connected to the first node N 1 , the other end (i.e., source) connected to the second node N 2 , and a gate receiving the reference voltage Vref.

In this structure, a final output signal is output through the output node Nout.

As described above, the input circuit for the semiconductor integrated circuit according to the second embodiment of the present invention has two stages. If the enable signal enable is at a low level, the third transistor TR 3 of the first input unit 310 is turned off, and the eleventh transistor TR 11 of the second input unit 320 is turned off. Therefore, the input circuit does not perform an amplifying operation on the input signal in. At this time, since the seventh transistor TR 7 is turned on, the final output signal out has a potential of a high level.

Meanwhile, if the enable signal is at a high level, the first input unit 310 and the second input unit 320 are activated, and perform an amplifying operation on the input signal in. The first input unit 310 amplifies the potential difference between the input signal in and the reference voltage Vref by a predetermined voltage gain, and outputs a result of the amplification. Also, the second input unit 320 amplifies the potential difference between the first output signal oin and the second output signal oref by a predetermined voltage gain, and outputs a result of the amplification.

The input circuit according to the second embodiment of the present invention includes the two input units, and performs the amplifying operations twice through the respective input units, such that the signal input from the outside of the input circuit is transmitted to the inside of the input circuit. Therefore, an amplified voltage gain of the input signal that is input to the input circuit and is subjected to an amplifying operation becomes larger than a voltage gain in the input circuit according to the related art that includes one differential amplifier, which reduces a signal distortion occurring due to the PVT.

Further, if a voltage level of the reference voltage Vref is decreased, a potential level of the second output signal oref is increased. As a result, a penetrating current the ninth transistor TR 9 of the pull-down unit 326 is increased, and a potential level at the first node N 1 is decreased. Since a penetrating current of the eighth transistor TR 8 of the pull-up compensating unit 324 is increased, the potential at the first node N 1 that is decreased by the ninth transistor TR 9 is compensated for.

Meanwhile, if the voltage level of the reference voltage Vref is increased, the potential level of the second output signal oref is decreased. As a result, the penetrating current of the ninth transistor TR 9 is decreased, and a potential level at the first node N 1 is increased. At this time, since a penetrating current of the twelfth transistor TR 12 of the pull-down compensating unit 328 is increased, the potential at the first node N 1 that is increased by the eighth transistor TR 8 is compensated for.

FIG. 5 is a diagram illustrating a structure of an input circuit for a semiconductor integrated circuit according to a third embodiment of the invention.

An input circuit 400 for a semiconductor integrated circuit according to the third embodiment of the present invention may include a first input unit 310 and a second input unit 320 a . The first input unit 310 may have the same structure as the first input unit 110 or 310 according to the above-described embodiments. Meanwhile, similar to the second input unit 320 according to the second embodiment of the invention, the second input unit 320 a includes a pull-up unit 322 a , a pull-up compensating unit 324 , a pull-down unit 326 a , and a pull-down compensating unit 328 . The second input unit 320 a according to still another embodiment of the present invention is different from the second input unit 320 in structures of the pull-up unit 322 a and the pull-down unit 326 a.

The pull-up unit 322 a includes a fifth transistor TR 5 that has one end (i.e., source) connected to a terminal of the external power supply voltage VDD, the other end (i.e., drain) and a gate commonly connected to the first node N 1 ; a sixth transistor TR 6 that has one end (i.e., source) connected to the terminal of the external power supply voltage VDD, the other end (i.e., drain) connected to the output node Nout, and a gate connected to the first node N 1 ; a seventh transistor TR 7 that has on end (i.e., source) connected to the terminal of the external power supply voltage VDD, the other end (i.e., drain) connected to the output node Nout, and a gate receiving the enable signal enable; a thirteenth transistor TR 13 that has one end (i.e., source) connected to the terminal of the external power supply voltage VDD, the other end (i.e., drain) connected to the first node N 1 , and a gate receiving the second output signal oref; and a fourteenth transistor TR 14 that has one end (i.e., source) connected to the terminal of the external power supply voltage VDD, the other end (i.e., drain) connected to the output node Nout, and a gate receiving the first output signal oin.

The pull-down unit 326 a includes a ninth transistor TR 9 that has one end (i.e., drain) connected to the first node N 1 , the other end (i.e., source) connected to the second node N 2 , and a gate receiving the second output signal oref; a tenth transistor TR 10 that has one end (i.e., drain) connected to the output node Nout, the other end (i.e., source) connected to the second node N 2 , and a gate receiving the first output signal oin; an eleventh transistor TR 11 that has one end (i.e., drain) connected to the second node N 2 , the other end (i.e., source) connected to a ground terminal, and a gate receiving the enable signal enable; a fifteenth transistor TR 15 that has one end (i.e., drain) and a gate commonly connected to the first node N 1 and the other end (i.e., source) connected to the second node N 2 ; and a sixteenth transistor TR 16 that has one end (i.e., drain) connected to the output node Nout, the other end (i.e., source) connected to the second node N 2 , and a gate connected to the first node N 1 .

In this structure, the first and sixth transistors TR 5 and TR 6 of the pull-up unit 322 a operate opposed to the thirteenth and fourteenth transistors TR 13 and TR 14 , and the ninth and tenth transistors TR 9 and TR 10 of the pull-down unit 326 a operate opposed to the fifteenth and sixteenth transistors TR 15 and TR 16 .

Therefore, the potential level variation widths of the first node N 1 and the output node Nout due to the variation in the potential level of the reference voltage Vref are decreased, and it is possible to reduce the final output signal out from being affected by the reference voltage Vref, which improves the reliability.

That is, since the input circuit for the semiconductor integrated circuit according to embodiments of the invention has two stages, the input circuit has a sufficient voltage gain. Therefore, even though the operation characteristics of the MOS transistors that form the input circuit are changed due to the variation in the PVT, stable operations can be performed. Further, even though the voltage level of the reference voltage for comparison with the input signal is varied, it is possible to compensate for the variation in the potential level of the output signal, and thus the output signal has constant duty characteristics. Accordingly, the duty characteristics of the output signal can be stabilized, and the margin in the setup/hold time of the semiconductor integrated circuit can be increased.

It will be apparent to those skilled in the art that various modifications and changes may be made without departing from the scope and spirit of the invention. Therefore, it should be understood that the above embodiments are not limiting, but illustrative in all aspects. The scope of the invention is defined by the appended claims rather than by the description preceding them, and therefore all changes and modifications that fall within metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the claims.

When the semiconductor integrated circuit operates at a high speed, a timing of a setup/hold time is reduced, but it is difficult to reduce a skew and a jitter in the input circuit, because of the variation in processing, temperature, and a voltage level. However, the input circuit according to an embodiment of the invention includes two stages, and the bias signal providing unit similar to the input circuit is used. As a result, the input circuit can operate without depending on the above-described environmental variations. Therefore, it is possible to increase an operation margin of the setup/hold timing, making it possible to design an input circuit capable of reducing the setup/hold time.