Abstract:
Data transmission circuits are provided. The data transmission circuit includes a control signal generator and an output driver. The control signal generator generates a pull-up control signal and a pull-down control signal by using a count signal that changes in response to a clock signal during a drive control period. The output driver receives an internal data signal and drives a transmission data signal in response to the pull-up control signal and the pull-down control signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority under 35 U.S.C. 119(a) to Korean Application No. 10-2013-0035770, filed on Apr. 2, 2013, in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    The current tendency in high-speed electronic systems is to transfer data between integration circuits included therein at high speed. Data signals transmitted between the integration circuits may be set to have small amplitudes in order to improve the data speed. Further, an output impedance of a data transmission circuit for transmitting the data signals should be matched with an impedance of a transmission line through which the data signals are transmitted so that the data signals having a small amplitude are not deformed or distorted. When the output impedance of the data transmission circuit is not matched with the impedance of the transmission line, the data signals may have abnormal waveforms due to overshoot or undershoot. In such a case, the data signals may not be transmitted at a high speed. 
         [0003]    On-die termination (ODT) is the technology where the termination resistor for impedance matching in the transmission lines is located inside a semiconductor device instead of on a printed circuit board. An ODT circuit may include a switching circuit to reduce power consumption. However, the impedance of the ODT circuits may vary according to process/voltage/temperature (PVT) conditions. Hence, a test for calibrating the impedance of the ODT circuits may be required prior to use of the ODT circuits. 
         [0004]    The impedance calibration test may be executed using a ZQ calibration circuit. The data transmission circuit may generate a code signal for calibrating a pull-up drive or a pull-down drive using a ZQ resistor connected to an external device and may calibrate the impedance of the ODT circuit using the code signal, thereby executing the impedance calibration test. 
       SUMMARY 
       [0005]    Various embodiments are directed to data transmission circuits. 
         [0006]    According to various embodiments, a data transmission circuit includes a control signal generator and an output driver. The control signal generator generates a pull-up control signal and a pull-down control signal by using a count signal that changes in response to a clock signal during a drive control period. The output driver receives an internal data signal and drives a transmission data signal in response to the pull-up control signal and the pull-down control signal. 
         [0007]    According to various embodiments, a data transmission circuit includes a count signal generator and a signal converter. The count signal generator is driven in response to an activation signal which is enabled during the drive control period to generate first and second count signals by performing counting operations under a control a clock signal. The signal converter outputs first and second pull-up control signals for controlling a pull-up drive of a transmission data signal by buffering opposite logic levels to the first and second count signals and outputs first and second pull-down control signals for controlling a pull-down drive of the transmission data signal by buffering the first and second count signals. 
         [0008]    According to an embodiment, a system includes a data transmission circuit. The data transmission circuit includes a control signal generator configured to generate a plurality of count signals in response to an activation signal; and an output driver configured to receive an internal data signal and drive a transmission data signal in response to a plurality of pull-up control signals and a plurality of pull-down control signals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Embodiments of the inventive concept will become more apparent in view of the attached drawings and accompanying detailed description, in which: 
           [0010]      FIG. 1  is a block diagram illustrating a configuration of a data transmission circuit according to an embodiment of the present invention; 
           [0011]      FIG. 2  is a block diagram illustrating an example of a count signal generator included in the data transmission circuit of  FIG. 1 ; 
           [0012]      FIG. 3  is a circuit diagram illustrating an example of a signal converter included in the data transmission circuit of  FIG. 1 ; 
           [0013]      FIG. 4  is a block diagram illustrating an example of an output driver included in the data transmission circuit of  FIG. 1 ; 
           [0014]      FIG. 5  is a circuit diagram illustrating an example of a pull-up pre-driver included in the output driver of  FIG. 4 ; 
           [0015]      FIG. 6  is a circuit diagram illustrating an example of a pull-down pre-driver included in the output driver of  FIG. 4 ; 
           [0016]      FIG. 7  is a circuit diagram illustrating an example of a driver included in the output driver of  FIG. 4 ; and 
           [0017]      FIGS. 8 and 9  are timing diagrams illustrating operations of data transmission circuits according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Example embodiments of the inventive concept will be described hereinafter with reference to the accompanying drawings. However, the example embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the inventive concept. 
         [0019]    Referring to  FIG. 1 , a data transmission circuit according to an embodiment of the present invention may be configured to include a control signal generator  1  and an output driver  2 . The control signal generator  1  may include a count signal generator  11  and a signal converter  12 . The count signal generator  11  may be driven in response to an activation signal ZQ_EN which is enabled during a drive control period and may generate first to fourth count signals CNT&lt;1:4&gt;. In an embodiment of the present invention, the first to fourth count signals CNT&lt;1:4&gt; may be generated by performing counting operations under control of a clock signal CLK. The signal converter  12  may generate first to fourth pull-up control signals PCNT&lt;1:4&gt; for controlling a pull-up driving force of a transmission data signal DQ and output first to fourth pull-down control signals NCNT&lt;1:4&gt; for controlling a pull-down driving force of the transmission data signal DQ in response to the first to fourth count signals CNT&lt;1:4&gt;. For example, the signal converter  12  may generate the first to fourth pull-down control signals NCNT&lt;1:4&gt; by buffering and outputting the first to fourth count signals CNT&lt;1:4&gt;. For example, the signal converter  12  may also generate the first to fourth pull-up control signals PCNT&lt;1:4&gt; by buffering and outputting opposite logic-levels to the first to fourth count signals CNT&lt;1:4&gt;. The output driver  2  may receive an internal data signal ID and may drive the transmission data signal DQ in response to the first to fourth pull-up control signals PCNT&lt;1:4&gt; and the first to fourth pull-down control signals NCNT&lt;1:4&gt;. The drive control period may be set to a period when an impedance calibration test is being carried out, but not limited thereto. 
         [0020]    Referring to  FIG. 2 , the count signal generator  11  may be configured to include a first counter  111 , a second counter  112 , a third counter  113  and a fourth counter  114 . The first counter  111  may output the first count signal CNT&lt; 1 &gt; by operating at every clock pulse of the clock signal CLK during the drive control period that the activation signal ZQ_EN is enabled to have a logic “high” level. The first count signal CNT&lt; 1 &gt; may be obtained by dividing the frequency of the clock signal CLK by  2 . The second counter  112  may output the second count signal CNT&lt; 2 &gt; by operating at every clock pulse of the first count signal CNT&lt; 1 &gt; during the drive control period that the activation signal ZQ_EN is enabled to have a logic “high” level. The second count signal CNT&lt; 2 &gt; may be obtained by dividing the frequency of the clock signal CLK by 4. The third counter  113  may output the third count signal CNT&lt; 3 &gt; by operating at every clock pulse of the second count signal CNT&lt; 2 &gt; during the drive control period that the activation signal ZQ_EN is enabled to have a logic “high” level. The third count signal CNT&lt; 3 &gt; may be obtained by dividing the frequency of the clock signal CLK by 8. The fourth counter  114  may output the fourth count signal CNT&lt; 4 &gt; by operating at every clock pulse of the third count signal CNT&lt; 3 &gt; during the drive control period that the activation signal ZQ_EN is enabled to have a logic “high” level. The fourth count signal CNT&lt; 4 &gt; may be obtained by dividing the frequency of the clock signal CLK by 16. If a frequency of the clock signal CLK increases, frequencies of the first to fourth count signals CNT&lt;1:4&gt; generated in the count signal generator  11  may also increase. 
         [0021]    Referring to  FIG. 3 , the signal converter  12  may be configured to include a first buffer  121  and a second buffer  122 . The first buffer  121  may generate the first to fourth pull-up control signals PCNT&lt;1:4&gt; by buffering and outputting opposite logic-levels to the first to fourth count signals CNT&lt;1:4&gt;. The second buffer  122  may generate the first to fourth pull-down control signals NCNT&lt;1:4&gt; by buffering and outputting opposite logic-levels to the first to fourth pull-up control signals PCNT&lt;1:4&gt;. 
         [0022]    Referring to  FIG. 4 , the output driver  2  may be configured to include a pull-up pre-driver  21 , a pull-down pre-driver  22  and a driver  23 . The pull-up pre-driver  21  may receive the internal data signal ID to output a pull-up signal PU driven by a drivability which is set according to the first to fourth pull-up control signals PCNT&lt;1:4&gt;. The pull-down pre-driver  22  may receive the internal data signal ID to output a pull-down signal PD driven by a drivability which is set according to the first to fourth pull-down control signals NCNT&lt;1:4&gt;. The driver  23  may output the transmission data signal DQ which is driven in response to the pull-up signal PU and the pull-down signal PD. 
         [0023]    Referring to  FIG. 5 , the pull-up pre-driver  21  may be configured to include first to fourth pull-up elements P 210 , P 212 , P 214  and P 216 , first to fourth pull-up switches P 211 , P 213 , P 215  and P 217 , first to fourth pull-down elements N 210 , N 212 , N 214  and N 216 , and first to fourth pull-down switches N 211 , N 213 , N 215  and N 217 . In an embodiment of the present invention, the first to fourth pull-up elements P 210 , P 212 , P 214  and P 216  and the first to fourth pull-up switches P 211 , P 213 , P 215  and P 217  may be PMOS transistors, and the first to fourth pull-down elements N 210 , N 212 , N 214  and N 216  and the first to fourth pull-down switches N 211 , N 213 , N 215  and N 217  may be NMOS transistors. 
         [0024]    The first to fourth pull-up elements P 210 , P 212 , P 214  and P 216  may be turned on to pull up the pull-up signal PU outputted from a first node ND 21  when the internal data signal ID has a logic “low” level. The first to fourth pull-up switches P 211 , P 213 , P 215  and P 217  may be respectively connected in series to the first to fourth pull-up elements P 210 , P 212 , P 214  and P 216  between a power supply terminal VDD and the first node ND 21 . Further, the first to fourth pull-up switches P 211 , P 213 , P 215  and P 217  may be turned on in response to the first to fourth pull-up control signals PCNT&lt;1:4&gt; having a logic “low” level, respectively. The first to fourth pull-down elements N 210 , N 212 , N 214  and N 216  may be turned on to pull down the pull-up signal PU when the internal data signal ID has a logic “high” level. The first to fourth pull-down switches N 211 , N 213 , N 215  and N 217  may be respectively connected in series to the first to fourth pull-down elements N 210 , N 212 , N 214  and N 216  between the first node ND 21  and a ground voltage terminal VSS. Further, the first to fourth pull-down switches N 211 , N 213 , N 215  and N 217  may be turned on in response to the first to fourth pull-down control signals NCNT&lt;1:4&gt; having a logic “high” level, respectively. As described above, the first to fourth pull-up control signals PCNT&lt;1:4&gt; and the first to fourth pull-down control signals NCNT&lt;1:4&gt; may be generated by buffering the first to fourth count signals CNT&lt;1:4&gt;. Thus, if frequencies of the first to fourth count signals CNT&lt;1:4&gt; increase, the number of enabled signals among the pull-up control signals PCNT&lt;1:4&gt; and the pull-down control signals NCNT&lt;1:4&gt; may also increase. In the event that the number of enabled signals among the pull-up control signals PCNT&lt;1:4&gt; and the pull-down control signals NCNT&lt;1:4&gt; increases, the number of turned-on switches among the pull-up switches P 211 , P 213 , P 215  and P 217  and the pull-down switches N 211 , N 213 , N 215  and N 217  may also increase to enhance a drivability for driving the pull-up signal PU. 
         [0025]    Referring to  FIG. 6 , the pull-down pre-driver  22  may be configured to include fifth to eighth pull-up elements P 220 , P 222 , P 224  and P 226 , fifth to eighth pull-up switches P 221 , P 223 , P 225  and P 227 , fifth to eighth pull-down elements N 220 , N 222 , N 224  and N 226 , and fifth to eighth pull-down switches N 221 , N 223 , N 225  and N 227 . In an embodiment of the present invention, the fifth to eighth pull-up elements P 220 , P 222 , P 224  and P 226  and the fifth to eighth pull-up switches P 221 , P 223 , P 225  and P 227  may be PMOS transistors, and the fifth to eighth pull-down elements N 220 , N 222 , N 224  and N 226  and the fifth to eighth pull-down switches N 221 , N 223 , N 225  and N 227  may be NMOS transistors. 
         [0026]    The fifth to eighth pull-up elements P 220 , P 222 , P 224  and P 226  may be turned on to pull up the pull-down signal PD outputted from a second node ND 22  when the internal data signal ID has a logic “low” level. The fifth to eighth pull-up switches P 221 , P 223 , P 225  and P 227  may be respectively connected in series to the fifth to eighth pull-up elements P 220 , P 222 , P 224  and P 226  between the power supply terminal VDD and the second node ND 22 . Further, the fifth to eighth pull-up switches P 221 , P 223 , P 225  and P 227  may be turned on in response to the first to fourth pull-up control signals PCNT&lt;1:4&gt; having a logic “low” level, respectively. The fifth to eighth pull-down elements N 220 , N 222 , N 224  and N 226  may be turned on to pull down the pull-down signal PD when the internal data signal ID has a logic “high” level. The fifth to eighth pull-down switches N 221 , N 223 , N 225  and N 227  may be respectively connected in series to the fifth to eighth pull-down elements N 220 , N 222 , N 224  and N 226  between the second node ND 22  and the ground voltage terminal VSS. Further, the fifth to eighth pull-down switches N 221 , N 223 , N 225  and N 227  may be turned on in response to the first to fourth pull-down control signals NCNT&lt;1:4&gt; having a logic “high” level, respectively. As described above, the first to fourth pull-up control signals PCNT&lt;1:4&gt; and the first to fourth pull-down control signals NCNT&lt;1:4&gt; may be generated by buffering the first to fourth count signals CNT&lt;1:4&gt;. Thus, if frequencies of the first to fourth count signals CNT&lt;1:4&gt; increase, the number of enabled signals among the pull-up control signals PCNT&lt;1:4&gt; and the pull-down control signals NCNT&lt;1:4&gt; may also increase. In the event that the number of enabled signals among the pull-up control signals PCNT&lt;1:4&gt; and the pull-down control signals NCNT&lt;1:4&gt; increases, the number of turned-on switches among the pull-up switches P 221 , P 223 , P 225  and P 227  and the pull-down switches N 221 , N 223 , N 225  and N 227  may also increase to enhance a drivability for driving the pull-down signal PD. 
         [0027]    Referring to  FIG. 7 , the driver  23  may configured to include a PMOS transistor P 231 , a resistor R 21 , a resistor R 22  and an NMOS transistor N 231 . The PMOS transistor P 231  and a resistor R 21  are connected in series between the power supply terminal VDD and a third node ND 23 . The resistor R 22  and an NMOS transistor N 231  are connected in series between the third node ND 23  and the ground voltage terminal VSS. The PMOS transistor P 231  may be turned on in response to the pull-up signal PU to pull up the transmission data signal DQ, and the NMOS transistor N 231  may be turned on in response to the pull-down signal PD to pull down the transmission data signal DQ. If a drivability of the pull-up pre-driver  21  for driving the pull-up signal PU and a drivability of the pull-down pre-driver  22  for driving the pull-down signal PD increase, the driver  23  may drive the transmission data signal DQ more quickly to increase a slew rate of the transmission data signal DQ. 
         [0028]    Operations of the data transmission circuit as set forth above will be described with reference to  FIGS. 8 and 9  in conjunction with an example that a frequency of the clock signal CLK is relatively high and an example that a frequency of the clock signal CLK is relatively low. 
         [0029]    As illustrated in  FIG. 8 , if the frequency of the clock signal CLK is relatively high, the number of times that the clock signal CLK is toggled may increase during the drive control period (from a point of time T11 to a point of time T20) when the activation signal ZQ_EN is enabled to have a logic “high” level. In an embodiment of the present invention, if a first pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T12, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “high(H)” level, a logic “low(L)” level, a logic “low(L)” level and a logic “low(L)” level, respectively. If a second pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T13, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “low(L)” level, a logic “high(H)” level, a logic “low(L)” level and a logic “low(L)” level, respectively. If a third pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T14, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “high(H)” level, a logic “high(H)” level, a logic “low(L)” level and a logic “low(L)” level, respectively. If a fourth pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T15, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “low(L)” level, a logic “low(L)” level, a logic “high(H)” level and a logic “low(L)” level, respectively. If a fifth pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T16, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “high(H)” level, a logic “low(L)” level, a logic “high(H)” level and a logic “low(L)” level, respectively. If a sixth pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T17, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “low(L)” level, a logic “high(H)” level, a logic “high(H)” level and a logic “low(L)” level, respectively. If a seventh pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T18, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “high(H)” level, a logic “high(H)” level, a logic “high(H)” level and a logic “low(L)” level, respectively. If an eighth pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T19, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “low(L)” level, a logic “low(L)” level, a logic “low(L)” level and a logic “high(H)” level, respectively. Since eight pulses of the clock signal CLK are sequentially applied to the count signal generator  11  during the drive control period (T11˜T20), a combination of the first to fourth count signals CNT&lt;1:4&gt; may have eight different values in this period. 
         [0030]    Referring to  FIG. 9 , if the frequency of the clock signal CLK is relatively low, the number of times that the clock signal CLK is toggled may decrease during the drive control period (from a point of time T21 to a point of time T25) when the activation signal ZQ_EN is enabled to have a logic “high” level. In an embodiment of the present invention, if a first pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T22, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “high(H)” level, a logic “low(L)” level, a logic “low(L)” level and a logic “low(L)” level, respectively. If a second pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T23, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “low(L)” level, a logic “high(H)” level, a logic “low(L)” level and a logic “low(L)” level, respectively. If a third pulse of the clock signal CLK is applied to the count signal generator  11  of the control signal generator  1  at a point of time T24, the first to fourth count signals CNT&lt;1:4&gt; may have a logic “high(H)” level, a logic “high(H)” level, a logic “low(L)” level and a logic “low(L)” level, respectively. Since three pulses of the clock signal CLK are sequentially applied to the count signal generator  11  during the drive control period (T21-T25), the first to fourth count signals CNT&lt;1:4&gt; may have three different values in this period. 
         [0031]    As a result, in the data transmission circuit according to an embodiment of the present invention, the number of values that the combination of the first to fourth count signals CNT&lt;1:4&gt; may have during a specific period may increase as the frequency of the clock signal CLK becomes higher. If the number of values that the combination of the first to fourth count signals CNT&lt;1:4&gt; may have during the specific period increases, the drivability for driving the pull-up signal PU and the pull-down signal PD may also increase to improve a slew rate of the transmission data signal DQ. That is, the data transmission circuit according to an embodiment of the present invention may transmit a transmission data signal having a high slew rate when the frequency of the clock signal CLK becomes higher. The data transmission circuit according to an embodiment of the present invention may transmit a transmission data signal having a low slew rate when the frequency of the clock signal CLK becomes lower. 
         [0032]    According to an embodiment of the present invention set forth above, a drivability for driving a transmission data signal may be controlled by a frequency of an external clock signal. Thus, a slew rate of the transmission data signal can be controlled according to the frequency of the external clock signal. 
         [0033]    The example embodiments of the inventive concept have been disclosed above for illustrative purposes. Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the inventive concept as disclosed in the accompanying claims.