Abstract:
A data input buffer for use in a semiconductor device, including: a detection unit for receiving a reference voltage signal and an input data signal through a first input terminal and a second input terminal respectively in order to detect a voltage level of the input data signal based on a result of comparing the input data signal with the reference voltage in response to a clock enable signal inputted through a third input terminal; and a noise elimination unit connected between the first input terminal and the third input terminal for eliminating a noise of the reference voltage signal.

Description:
FIELD OF INVENTION 
   The present invention relates to a semiconductor device; and, more particularly, to a data input buffer for use in an electronic circuit. 
   DESCRIPTION OF PRIOR ART 
   Generally, a semiconductor device such as a semiconductor memory device is operated according to various input signals. That is, based on various logic levels of the input signals, operations of the semiconductor device are determined. An output signal of a semiconductor device can be used as an input signal of another semiconductor device in a same system. 
   An input buffer is employed for inputting an input signal to a semiconductor device by buffering the input signal. A simple type of the input buffer is a static input buffer. The static input buffer is formed by connecting a p-type metal oxide semiconductor (PMOS) transistor with an n-type metal oxide semiconductor (NMOS) transistor in series between a power supply voltage and a ground voltage having an operation of an inverter. 
   Although the static input buffer has a simple structure, the static input buffer requires an input signal to have a relatively long signal swing between a logic high level and a logic low level since the static input buffer is easily influenced by a noise. Therefore, the static input buffer is not suitable for an input signal having a short signal swing or a high-frequency system. 
   Therefore, for overcoming the above-mentioned problem of the static input buffer, a differential amplifier input buffer has been developed. The differential amplifier input buffer is usually called a dynamic input buffer. 
     FIG. 1  is a schematic circuit diagram showing a conventional input buffer. 
   As shown, the conventional input buffer includes a detection unit  10  for detecting a voltage level of a input data signal IN by comparing a voltage level of a reference voltage VREF with the voltage level of the input data signal IN; and a buffering unit  15  for buffering an output signal of the detection unit  10 . 
   In detail, the detection unit  10  includes a first to a fourth PMOS transistors Q 1  to Q 4 , a first to a third NMOS transistors Q 5  to Q 7  and an inverter IN 1 . 
   A gate of the first NMOS transistor Q 5  receives the reference voltage VREF and a gate of the second NMOS transistor Q 6  receives the input data signal IN. 
   The second PMOS transistor Q 2  is connected between a power supply voltage VDD and the fifth NMOS transistor Q 5  and the third PMOS transistor Q 3  is connected between the power supply voltage VDD and the sixth NMOS transistor Q 6 . Gates of the second and the third PMOS transistors Q 2  and Q 3  are commonly coupled to a first node N 1 . 
   The inverter IN 1  inverts a clock enable bar signal /CKE to generate a clock enable signal CKE. The third NMOS transistor Q 7  is connected between sources of the first and the second NMOS transistors Q 5  and Q 6  and a ground voltage VSS. A gate of the third NMOS transistor Q 7  receives the clock enable signal CKE. 
   The first PMOS transistor Q 1  is connected between the power supply voltage VDD and the first node N 1  and receives the clock enable signal CKE through a gate of the first PMOS transistor Q 1 . The fourth PMOS transistor Q 4  is connected between the power supply voltage VDD and an output node N 2  and receives the clock enable signal CKE through a gate of the fourth PMOS transistor Q 4 . 
   Meanwhile, the buffering unit  15  includes odd numbers of inverters for receiving an output signal of the detection unit  10  in order to generate an internal data signal BIN. 
   If the input data signal IN is inputted to the second NMOS transistor Q 6  having a high voltage, the detection unit  10  detects that a voltage level of the input data signal IN is higher than that of the reference voltage VREF. Herein, the reference voltage has a constant voltage level, i.e., about half of the power supply voltage VDD. The reference voltage VREF is inputted to a semiconductor device through a particular input pin by an external circuit or is internally generated in the semiconductor device. 
   The first PMOS transistor Q 5  receiving the reference voltage VREF has a constant current, i.e., a first current i 1  flown on the first PMOS transistor Q 5 . A second current i 2  flown on the second NMOS transistor Q 6  is varied according to a voltage level of the input data signal IN. The detection unit  10  determines a voltage level of the output node N 2  based on a result of comparing the first current i 1  with the second current i 2 . 
   When the clock enable bar signal /CKE is activated as a logic low level, the third NMOS transistor Q 7  is turned on and the first and the fourth PMOS transistors Q 1  and Q 4  are turned off. Thus, the detection unit  10  is normally operated. 
   Thereafter, when the clock enable bar signal /CKE is inactivated as a logic high level, the third NMOS transistor Q 7  is turned off and the detection unit  10  is disabled. The first and the fourth PMOS transistors Q 1  and Q 4  are turned off precharging the first node N 1  and the output node N 2  as a logic high level respectively. Therefore, a current flow in the detection unit  10  is prevented for reducing power consumption. 
   Herein, when the clock enable bar signal /CKE is activated as a logic low level again, i.e., when the clock enable signal CKE is activated as a logic high level, a voltage level of the first node N 1  is lowered from the power supply voltage VDD to a half voltage of the power supply voltage VDD. At this time, the voltage variation of the first node N 1  causes a coupling noise of the reference voltage VREF since there is a parasitic capacitance C_N 1  between the first node N 1  and an input terminal of the reference voltage VREF. 
     FIG. 2  is a timing diagram showing variations of the reference voltage VREF according to the clock enable signal CKE after precharging the input terminal of the reference voltage REF by using a capacitor having a constant capacitance. 
   When the clock enable signal CKE is changed from a logic low level to a logic high level, a voltage level of the reference voltage VREF is sloped downward due to the parasitic capacitance C_N 1 . On the contrary, when the clock enable signal CKE is changed from a logic low level to a logic high level, a voltage level of the reference voltage VREF is sloped upward due to the parasitic capacitance C_N 1 . Therefore, according to the conventional input buffer, it is difficult to eliminate the coupling noise of the reference voltage VREF. 
   Generally, for a high-speed data transmission, a data signal swing width from a high level to a low level is required to be short. In addition, also for reducing power consumption, a short signal swing width is desired. 
     FIG. 3  is a timing diagram showing variations of the reference voltage VREF and a data signal. Herein, it is assumed that a signal swing width of the data signal is very small having a value of about 200 mV. A valid data eye of the data signal is decreased as the signal swing width is decreased. 
   As shown in the case (A), if the reference voltage VREF ideally has a constant voltage level, i.e., has no noise, a correct logic level of the data signal can be easily detected even if the signal swing width is very small. 
   However, as shown in the case (A), if the reference voltage VREF is fluctuated due to a noise, it is difficult to detect a correct logic level of the data signal because of the small signal swing width of the data signal. 
   Meanwhile, generally, a data input buffer includes a plurality of input buffers each of which commonly receives the reference voltage VREF and the clock enable bar signal /CKE as shown in  FIG. 4 . If a noise is generated from one of the plurality of input buffers, the noise may cause other noises of the other input buffers. 
   SUMMARY OF INVENTION 
   It is, therefore, an object of the present invention to provide a data input buffer capable of eliminating a noise of a reference voltage. 
   In accordance with an aspect of the present invention, there is provided a data input buffer for use in a semiconductor device, including: a detection unit for receiving a reference voltage signal and an input data signal through a first input terminal and a second input terminal respectively in order to detect a voltage level of the input data signal based on a result of comparing the input data signal with the reference voltage in response to a clock enable signal inputted through a third input terminal; and a noise elimination unit connected between the first input terminal and the third input terminal for eliminating a noise of the reference voltage signal. 
   In accordance with another aspect of the present invention, there is provided a data input buffer for use in a semiconductor device, including: a first NMOS transistor whose one end is connected to a first node for receiving a reference voltage signal through a gate of the first NMOS transistor; a second NMOS transistor whose one end is connected to a second node for receiving an input data signal through a gate of the second NMOS transistor; a third NMOS transistor connected between the first and the second NMOS transistors and a ground voltage for receiving a clock enable signal through a gate of the third NMOS transistor; a first PMOS transistor connected between a power supply voltage and the first node for receiving the clock enable signal through a gate of the first PMOS transistor; a second PMOS transistor whose one end is connected to the power supply voltage and the other end and a gate are commonly coupled to the first node; a third PMOS transistor connected between the power supply voltage and the second node; a fourth PMOS transistor connected between the power supply voltage and the second node; and a capacitive element connected between the gate of the first NMOS transistor and the gate of the third NMOS transistor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic circuit diagram showing a conventional input buffer; 
       FIG. 2  is a timing diagram showing variations of a reference voltage according to a clock enable signal; 
       FIG. 3  is a timing diagram showing variations of the reference voltage and a data signal; 
       FIG. 4  is a block diagram showing a data input buffer unit including a plurality of input buffers; 
       FIG. 5  is a schematic circuit diagram showing a data input buffer in accordance with a preferred embodiment of the present invention; and 
       FIG. 6  is a timing diagram showing variations of a reference voltage according to a clock enable signal shown in  FIG. 5 . 
   

   DETAILED DESCRIPTION OF INVENTION 
   Hereinafter, a data input buffer in accordance with the present invention will be described in detail referring to the accompanying drawings. 
     FIG. 5  is a schematic circuit diagram showing a data input buffer in accordance with a preferred embodiment of the present invention. 
   As shown, the data input buffer includes a detection unit  20  including a metal oxide semiconductor (MOS) type differential amplifier for detecting a voltage level of an input data signal IN comparing the voltage level of the input data signal IN with a voltage level of the reference voltage VREF; and a buffering unit  15  for buffering an output signal of the detection unit  15  to generate an internal data signal BIN. 
   The detection unit  20  includes a first to a fourth p-type metal oxide semiconductor (PMOS) transistors Q 1  to Q 4 , a first to a third n-type metal oxide semiconductor (NMOS) transistors Q 5  to Q 7 , an inverter INV and a noise elimination unit  30 . 
   A gate of the first NMOS transistor Q 5  receives the reference voltage VREF and a gate of the second NMOS transistor Q 6  receives the input data signal IN. 
   The second PMOS transistor Q 2  is connected between a power supply voltage VDD and the fifth NMOS transistor Q 5  and the third PMOS transistor Q 3  is connected between the power supply voltage VDD and the sixth NMOS transistor Q 6 . Gates of the second and the third PMOS transistors Q 2  and Q 3  are commonly coupled to a first node N 1 . 
   The inverter INV inverts a clock enable bar signal /CKE to generate a clock enable signal CKE. The third NMOS transistor Q 7  is connected between sources of the first and the second NMOS transistors Q 5  and Q 6  and a ground voltage VSS. A gate of the third NMOS transistor Q 7  receives the clock enable signal CKE. 
   The first PMOS transistor Q 1  is connected between the power supply voltage VDD and the first node N 1  and receives the clock enable signal CKE through a gate of the first PMOS transistor Q 1 . The fourth PMOS transistor Q 4  is connected between the power supply voltage VDD and an output node N 2  and receives the clock enable signal CKE through a gate of the fourth PMOS transistor Q 4 . 
   The noise elimination unit  30  is connected between an input terminal of the reference voltage VREF and the gate of the third NMOS transistor Q 7 . 
   The buffering unit  15  includes odd numbers of CMOS inverters connected in series for buffering the output signal of the detection unit  15 . 
   The noise elimination unit  30  includes a fourth NMOS transistor Q 8 . A gate of the fourth NMOS transistor Q 8  is coupled to the input terminal of the reference voltage VREF and one terminal of the fourth NMOS transistor Q 8  is coupled to the gate of the third NMOS transistor Q 7 . The other terminal of the fourth NMOS transistor Q 8  is floated. Herein, a gate capacitance of the fourth NMOS transistor Q 8  is half of a capacitance of a parasitic capacitor C_N 1 . That is, since it is assumed that a signal swing width at the first node N 1  according to a transition of the clock enable signal CKE is half of a signal swing width of the clock enable signal CKE, the gate capacitance of the fourth NMOS transistor Q 8  is adjusted to have half of the capacitance of the parasitic capacitor C_N 1  so that coupling charges generated by the parasitic capacitor C_N and the gate capacitance can be equal. 
   Operations of the data input buffer are described below referring to  FIG. 5 . 
   Operations of the detection unit  20  according to the input data signal IN are similar to those of the detection unit  10  shown in  FIG. 1 . 
   That is, when the clock enable bar signal /CKE is activated as a logic low level, the third NMOS transistor Q 7  is turned on and the first and the fourth PMOS transistors Q 1  and Q 4  are turned off. Thus, the detection unit  20  is normally operated to determine a voltage level of the output node N 2  based on a result of comparing a first current i 1  flown on the first NMOS transistor Q 5  and a second current i 2  flown on the second NMOS transistor Q 6 . 
   Thereafter, when the clock enable bar signal /CKE is inactivated as a logic high level, the third NMOS transistor Q 7  is turned off and the detection unit  20  is disabled. The first and the fourth PMOS transistors Q 1  and Q 4  are turned off precharging the first node N 1  and the output node N 2  as a logic high level respectively. 
   Herein, when the clock enable bar signal /CKE is activated as a logic low level again, i.e., when the clock enable signal CKE is activated as a logic high level, a voltage level of the first node N 1  is lowered from the power supply voltage VDD to a half voltage of the power supply voltage VDD. At this time, the voltage variation of the first node N 1  causes a coupling noise of the reference voltage VREF since there is the parasitic capacitance C_N 1  between the first node N 1  and the input terminal of the reference voltage VREF. However, the coupling noise of the reference voltage VREF is eliminated by the gate capacitance of the fourth NMOS transistor Q 8 . 
     FIG. 6  is a timing diagram showing variations of the reference voltage VREF according to the clock enable signal CKE after precharging the input terminal of the reference voltage REF by using a capacitor having a constant capacitance. 
   When the clock enable signal CKE is changed from a logic low level to a logic high level, a voltage level of the reference voltage VREF is lowered by the capacitance of the parasitic capacitor C_N 1 . However, at this time, the voltage level of the reference voltage VREF is also raised by the gate capacitance of the fourth NMOS transistor Q 8 . Therefore, since the coupling charges generated by the parasitic capacitor C_N 1  and the gate capacitance are the same, the voltage level of the reference voltage VREF is not changed holding a constant voltage level. 
   Similarly, when the clock enable signal CKE is changed from a logic high level to a logic low level, a voltage level of the reference voltage VREF is raised by the capacitance of the parasitic capacitor C_N 1 . However, at this time, the voltage level of the reference voltage VREF is also lowered by the gate capacitance of the fourth NMOS transistor Q 8 . Therefore, as above-mentioned, the voltage level of the reference voltage VREF is not changed holding a constant voltage level. 
   Although the preferred embodiment is described assuming that the gate capacitance of the fourth NMOS transistor Q 8  is half of the parasitic capacitance, the gate capacitance of the forth NMOS transistor Q 8  can have other values for generating same coupling charges of the parasitic capacitance and the gate capacitance. For this purpose, an equation shown below can be applied.
 
Q=CV  Eq. 1
 
   Herein, Q is a coupling charge, C is a capacitance and V is a voltage between terminals of a capacitor. 
   In addition, although the preferred embodiment employs an NMOS transistor as the noise elimination unit, another capacitive element such as a PMOS transistor can be adopted fro the noise elimination unit. 
   Further, although the preferred embodiment forms the detection unit as an NMOS type differential amplifier, i.e., current mirroring transistors are connected to the power supply voltage and a bias transistor is connected to the ground voltage, a PMOS type differential amplifier also can be employed for the detection unit providing a bias transistor and current mirroring transistors to the power supply voltage and the ground voltage respectively. In this case, the clock enable bar signal /CKE can be directly inputted to gates of MOS transistors placed at the same positions Q 1 , Q 4  and Q 8  shown in  FIG. 5 . 
   As a result, in accordance with the present invention, a coupling noise of a reference voltage generated due to a parasitic capacitance can be eliminated. Therefore, even though a data signal swing width is decreased for reducing power consumption, an enough data sensing margin time can be obtained. 
   The present application contains subject matter related to Korean patent application No. 2004-87668, filed in the Korean Patent Office on Oct. 30, 2004, the entire contents of which being incorporated herein by reference. 
   While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.