Abstract:
A system having a transmission unit transmitting an output data signal formed from output data and related error detection code and a corresponding receiving unit. The output data signal is pre-emphasized by a pre-emphasis driver in the transmission unit. The receiving unit includes an equalizer equalizing the received output data signal and an error detector analyzing the error detection code to determine whether a bit error is present in the received data. Upon successive data transmission failures either an equalization coefficient in the equalizer or a pre-emphasis coefficient in the pre-emphasis driver are changed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a data transmitting and receiving system. More particularly, the present invention relates to a data transmitting and receiving system using an equalizer. 
         [0003]    This application claims the benefit of Korean Patent Application No. 2006-69336, filed Jul. 24, 2006, the subject matter of which is hereby incorporated by reference. 
         [0004]    2. Description of Related Art 
         [0005]    Devices for inputting/outputting data are prone to errors (typically, referred to as “bit errors”) in the transmission of data caused, for example, by various random and systematic noise effects. 
         [0006]    The frequency of bit errors in a data communication system may be expressed in terms of a “bit error rate (BER)”, which is the ratio of incorrectly received data bits relative to a total number of data bits received during predetermined period of time. For example, a data channel having a BER of 10 −4  will receive an average of one incorrect (i.e., errant) data bit per every 10 4  data bits communicated through the channel. The BER of a given channel will vary with the speed of data transmission, channel length, and so on. Also, bit errors are mostly caused by noise in communication lines. Thus, a channel may be defined in its data communication capabilities by its inherent noise characteristics which determine most bit errors. In order to provide reliable data communication within contemporary systems, a data channel should have a BER in the order of 10 −12  or lower. 
         [0007]    As technology has developed, numerous techniques for eliminating or reducing noise have been proposed, but it remains practically impossible to completely eliminate all bit errors. Therefore, various error detection and/or correction codes are being conventionally employed to improve the performance of data channels. Of the many error detection/correction codes, one of the simplest and most widely-used is referred to as a cyclic redundancy checker (CRC). 
         [0008]    A CRC method determines a check value for detecting bits errors in data received through a channel. More specifically, an initial CRC value is calculated in accordance with given data, added to the data, and transmitted from a transmitter. Thereafter, a new CRC value is calculated on the basis of the data actually received by a receiver at the other end of the channel. The initial CRC value and the new CRC value are compared within the receiver or a circuit associated with the receiver. When the two CRC values are determined to be different, bit error induced by noise in data channel are indicated. When an excessive or uncorrectable number of bit error(s) are detected, an error signal may be returned from receiver to the transmitter and data may be re-transmitted. Assuming that most of the bit errors apparent in the first data transmission are due to random noise effects, the re-transmission often results in effective data communication. 
         [0009]    Systematic noise in a data channel, such as inter-channel crosstalk, inter-symbol interference (ISI), and simultaneous switching noise (SSN), poses a different set of considerations and implicates a number of different bit error detection and correction schemes. This is particularly true for high speed data communication systems. 
         [0010]    Consider for example the block diagram of a conventional data transmitting and receiving system shown in  FIG. 1 . In  FIG. 1 , a transmission unit  10  includes a transmission controller  11 , an error detection code generator  12 , a parallel-serial converter  13 , an output driver  14 , a pre-emphasis controller  17 , a receiving driver  18 , and a re-transmission determiner  19 . 
         [0011]    A receiving unit  20  includes an input driver  21 , a serial-parallel converter  25 , a receiving controller  26 , an error detector  27 , a re-transmission requester  28 , and a transmission driver  29 . 
         [0012]    Data channels (e.g., Ch, ChB, through ChR) communicate data between transmission unit  10  and receiving unit  20 . 
         [0013]    As transmission controller  11  outputs k-bits output data (dout), error detection code generator  12  generate s-bits error detection code (ec). Parallel-serial converter  13  receives the k-bits output data (dout) and s-bits error detection code (ec), converts them into a single serial stream of data, and outputs differential output data (do and doB) derived from the serial stream of data. 
         [0014]    As illustrated, output driver  14  includes a transmission driver  15  and a pre-emphasis driver  16 . Output driver  14  receives the differential output data (do and doB) and generates differential data signals (DO and DOB). In its operation, transmission driver  15  performs impedance-matching the received differential output data (do and doB) with channels (Ch and ChB), differentially amplifies this data, and outputs the amplified, differential output data. Pre-emphasis driver  16  modifies the differential output data (do and doB) in relation to a pre-emphasis control signal (pre_con) provided by pre-emphasis controller  17 . Following pre-emphasis, the amplified differential output data (do and doB) are transmitted as data signals (DO and DOB). That is, output driver  14  combines the outputs of transmission driver  15  and pre-emphasis driver  16  to generate pre-emphasized data signals (DO and DOB) which are communicated over channels Ch and ChB. 
         [0015]    Inevitably, the data signals (DO and DOB) are distorted during respective transmission over channels Ch and ChB to become errant data signals (DI and DIB). The degree and type of data distortions will vary by channel. 
         [0016]    Input driver  21  includes a receiving driver  22  and a receiving equalizer  23 . Input driver  21  performs impedance matching in order to receive as much of the errant data signals (DI and DIB) through the channels Ch and ChB as possible. In so doing input driver  21  prevents undesired signal reflections, corrects certain data distortions caused by transmission characteristics of channels Ch and ChB, and subsequently outputs differential input data (di and diB). Then, receiving equalizer  23  equalizes the differential input data (di and diB) in response to an equalization control signal (eq_con) provided by an equalizer controller  24 . 
         [0017]    The serial-parallel converter  25  converts the serially-provided differential input data (di and diB) into parallel-provided k-bits input data (din) subsequently communicated to receiving controller  26  and s-bits error detection code (ec) subsequently communicated to error detector  27  in addition to the k-bits input data (din). 
         [0018]    Error detector  27  analyzes the input data (din) and the error detection code (ec) and derives an error signal (er) when there one or more bit error(s) are present in the input data (din). 
         [0019]    In the illustrated example, receiving controller  26  ignores the input data (din) when it contains one or more bit error(s) (or more bit error than can be compensated at the receiver side). However, when the input data (din) is error free, receiving controller  26  proceeds forward with the indicated operation. 
         [0020]    In response to the error signal (er) from error detector  27 , re-transmission requester  28  generates an error indication data (edo) indicating a request for data re-transmission, and communicates this signal to transmission unit  10  via transmission driver  29  and data channel ChR. In this example, transmission driver  29  receives the error indication data (edo) and converts it into an error indication signal (EDO) in relation to the transmission characteristics of channel ChR. 
         [0021]    In turn, the error indication signal (EDO) may become distorted into distorted error indication signal (EDI) during communication through the channel ChR. 
         [0022]    Receiving driver  18  receives the distorted error indication signal (EDI), corrects the distortion, and outputs a corrected error indication signal (edi). In response to the corrected error indication signal (edi), re-transmission determiner  19  outputs a re-transmission signal (retry) to transmission controller  11  when re-transmission is necessary and allows transmission controller  11  to re-transmit the errantly received data. 
         [0023]    In the above description, “pre-emphasis” refers to a method of pre-emphasizing the relatively higher frequency components of output data signals at the transmitter since such signal components tend to undergo disproportionate attenuation during transmission. The pre-emphasis control signal (pre_con) is used as an optimal pre-emphasis coefficient adapted to minimize inter-symbol interference (ISI) between data bits due to the unique channel transmission characteristics. 
         [0024]    Similarly, receiving equalizer  23  is configured in consideration the unique transmission characteristics of the channel. The equalization control signal (eq_con) is used as an optimal equalization coefficient that enables maximum signal decoding. 
         [0025]    In general, the pre-emphasis coefficient and the equalization coefficient are pre-set within a data transmitting and receiving system. In other words, the pre-emphasis coefficient and the equalization coefficient are determined in consideration of system characteristics including channel characteristics in order to optimize the data transmitting and receiving system against systematic noise, as opposed to random noise. Therefore, when receiving unit  20  detects an error in the input data (din) and subsequently outputs an error indication signal (EDO) to transmission unit  10 , transmission unit  10  necessarily assumes that the error has been caused by random noise effects. If that assumption proves correct, it is expected that the randomly appearing noise will not be present during re-transmission. As a result, data may be re-transmitted under the in the belief that it will be communicated without error. 
         [0026]    However, in practice it is not easy to optimize the pre-emphasis and equalization coefficients of the data transmitting and receiving system. Even if it were, the pre-emphasis and equalization coefficients often need to be changed under various circumstances. In order to change the pre-set coefficients, conventional data transmitting and receiving systems require re-initialization. For example, a conventional data transmitting and receiving system must stop transmitting data, enter a mode setting operation, and output test data related to the mode setting operation. As a result, the performance of the conventional data transmitting and receiving system deteriorates. In addition, the data transmitting and receiving system may still generate bit errors under changing circumstances in spite of periodically performed mode setting operations. 
       SUMMARY OF THE INVENTION 
       [0027]    Embodiments of the invention provides a data transmitting and receiving system capable of maintaining in real time an optimal data communication state by controlling various coefficients applied to transmitted and received data. 
         [0028]    In one embodiment, the invention provides a data transmitting and receiving system comprising; a transmission unit transmitting an output data signal derived from output data and associated error detection code, the transmission unit comprising a pre-emphasis driver configured to pre-emphasize the output data signal before transmission, a channel having determined transmission characteristics and configured to communicate the output data signal from the transmission unit to a receiving unit, wherein the receiving unit comprises; an equalizer responsive to an equalization coefficient and configured to equalize the received output data signal, and an error detector configured to analyze input data and associated error detection code derived from the received output data signal and determine whether a bit error is present in the input data and generate an error signal upon determining the presence of a bit error, wherein upon determining successive bit errors in the input data, the receiving unit causes the equalization coefficient to be changed. 
         [0029]    In another embodiment, the invention provides a data transmitting and receiving system comprising; a transmission unit configured to transmit output data signals via a channel to a receiving unit, wherein the transmission unit comprises; a transmission controller providing output data and controlling transmission of an output data signal, an output driver receiving the output data, and amplifying and pre-emphasizing the output data to generate the output data signal, wherein a pre-emphasis coefficient applied within the output driver defines the pre-emphasis of the output data signal, and a re-transmission determiner applying a re-transmission signal to the transmission controller in response to a return error indication signal associated with the output data as provided by the receiving unit, and a receiving unit configured to receive the output data signal from the channel, wherein the receiving unit comprises; an equalizer deriving input data by applying an equalization coefficient to the received output data signal, an error detector analyzing the input data and generating an error signal upon determining that the input data contains a bit error, and a re-transmission requestor generating the return error indication signal upon each occurrence of receiving the error signal from the error detector, wherein upon receiving N successive error signals associated with the output data signal, where N is a positive integer greater than 1, either: (a) the re-transmission requestor generates an equalization correction signal that changes the equalization coefficient applied in the equalizer; or (b) the re-transmission determiner generates a pre-emphasis correction signal that changes the pre-emphasis coefficient. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a block diagram of a conventional data transmitting and receiving system. 
           [0031]      FIG. 2  is a block diagram of a data transmitting and receiving system according to an exemplary embodiment of the present invention. 
           [0032]      FIGS. 3A and 3B  are circuit diagrams of an output driver shown in  FIG. 2 . 
           [0033]      FIGS. 4A and 4B  are block diagrams illustrating the operation of an equalizer. 
           [0034]      FIG. 5  is a block diagram of an input driver shown in  FIG. 2 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    A data transmitting and receiving system according to an exemplary embodiment of the present invention will now be described more fully hereinafter with reference to the accompanying drawings. 
         [0036]      FIG. 2  is a block diagram of a data transmitting and receiving system according to an exemplary embodiment of the present invention. 
         [0037]    The data transmitting and receiving system includes a transmission unit  100  for transmitting data, a receiving unit  200  for receiving data, and channels Ch, ChB, and ChR for transmitting data between transmission unit  100  and receiving unit  200 . 
         [0038]    Transmission unit  100  includes a transmission controller  110 , an error detection code generator  120 , a parallel-serial converter  130 , an output driver  140 , a pre-emphasis controller  170 , a receiving driver  180 , and a re-transmission determiner  190 . 
         [0039]    Receiving unit  200  includes an input driver  210 , an equalizer controller  240 , a serial-parallel converter  250 , a receiving controller  260 , an error detector  270 , a re-transmission requester  280 , and a transmission driver  290 . 
         [0040]    As transmission controller  110  outputs k-bits output data (dout), error detection code generator  120  outputs s-bits error detection code (ec) associated with the output data (dout). Parallel-serial converter  130  receives the k-bits output data (dout) and the s-bits error detection code (ec), performs a parallel to serial conversion, and outputs differential output data (do and doB). 
         [0041]    Output driver  140  receives the differential output data (do and doB), converts this data in relation to the transmission characteristics of channels Ch and ChB, and generates output data signal (DO and DOB). 
         [0042]    In the illustrated embodiment, output driver  140  includes a transmission driver  150  and a pre-emphasis driver  160 . Transmission driver  150  performs impedance-matching and differential amplification of the differential output data (do and doB). Pre-emphasis driver  160  converts the differential output data (do and doB) based on the characteristics of channels Ch and ChB in response to a pre-emphasis control signal (pre_con) provided by pre-emphasis controller  170 , and outputs the converted data. 
         [0043]    Output driver  140  combines the output signals from transmission driver  150  and the output signals from pre-emphasis driver  160  to generate output data signals (DO and DOB) suitable for transmission over channels Ch and ChB. 
         [0044]    Channels Ch and ChB communicate the output data signals (DO and DOB) provided by transmission unit  100  to receiving unit  200  as distorted data signals (DI and DIB). That is, distorted data signals (DI and DIB) correspond respectively to the output data signals (DO and DOB), but have been distorted by the unique transmission characteristics of channels Ch and ChB. 
         [0045]    Input driver  210  of receiving unit  200  includes a receiving driver  220  and a receiving equalizer  230  adapted to receive the distorted data signals (DI and DIB). Receiving driver  220  performs impedance matching in order to receive as much of the distorted data signals (DI and DIB) as possible without any undesired signal reflections. Also, receiving equalizer  230  restores data integrity to the distorted data signals (DI and DIB) in relation to an equalization control signal (eq_con) provided by equalizer controller  240 , and thereafter outputs differential input data (di and diB). 
         [0046]    Serial-parallel converter  250  receives the differential input data (di and diB), performs a serial to parallel conversion, and outputs k-bits input data (din) to receiving controller  260 , and outputs s-bits error detection code (ec) along with the k-bits input data (din) to error detector  270 . 
         [0047]    Error detector  270  analyzes the input data (din) and the error detection code (ec), determines whether an error is present in the input data (din), and outputs an error signal (er) to receiving controller  260  and re-transmission requester  280  indicating the error in the input data (din). 
         [0048]    Receiving controller  260  ignores the input data (din) when it contains an error, but regularly performs an indicated operation when the input data (din) is error free. 
         [0049]    Re-transmission requester  280  outputs error indication data (edo) and a corresponding equalization correction signal (con 2 ) in response to the error signal (er). Equalizer controller  240  receives the equalization correction signal (con 2 ) from re-transmission requester  280  when it is necessary to adjust the equalization coefficient of receiving equalizer  230 , and thereby change the value of the equalization control signal (eq_con). 
         [0050]    Transmission driver  290  impedance matches the error indication data (edo) in relation to the transmission characteristics of the “return” channel ChR, amplifies the error indication data (edo), and thereby generates an error indication signal (EDO). 
         [0051]    The error indication signal (EDO) may become distorted error indication signal (EDI) during its return communication through channel ChR to transmission unit  100 . Receiving driver  180  of transmission unit  100  corrects distortion in the distorted error indication signal (EDI) to form return error indication data (edi). 
         [0052]    In response to the return error indication data (edi), re-transmission determiner  190  outputs a re-transmission signal (retry) and a pre-emphasis correction signal (con 1 ). The re-transmission signal (retry) is applied to transmission controller  110  in order to request re-transmission of the errant data, and the pre-emphasis correction signal (con 1 ) is applied to pre-emphasis controller  170  in order to change the pre-emphasis control signal (pre_con). 
         [0053]    In the data transmitting and receiving system shown in  FIG. 2 , when a bit error is apparent in the input data (din), it is assumed that the error is caused by random noise in the data channel, and a re-transmission of data is requested. However, when errors are detected in the same packet of input data (din) more than a predetermined number of times (i.e., following “N” retry attempts), it is assumed that the errors are being caused by systematic noise, so that the equalization coefficient used by receiving equalizer  230  and/or the pre-emphasis coefficient used by pre-emphasis driver  160  should be corrected. For example, when errors are detected in the same input data (din) twice or more, the equalization coefficient and/or the pre-emphasis coefficient may be corrected accordingly. 
         [0054]    Thus, after transmission unit  100  first transmits the output data signals (DO and DOB) and error detector  270  in receiving unit  200  detects an error, re-transmission requester  270  does not output the equalization correction signal (con 2 ), but outputs only the error indication data (edo). Also, when the corresponding error indication signal (EDO) is output from transmission driver  290  of receiving unit  200  to transmission unit  100 , re-transmission determiner  190  does not generate the pre-emphasis correction signal (con 1 ), but outputs only the re-transmission signal (retry) to allow transmission unit  100  to re-transmit data. 
         [0055]    Therefore, since re-transmission requester  280  and re-transmission determiner  190  do not output the correction signals (con 2  and con 1 ), respectively, the pre-emphasis control signal (pre_con) and the equalization control signal (eq_con) output from pre-emphasis controller  170  and equalization controller  240  are unchanged. 
         [0056]    However, if an error is again detected in re-transmitted data, re-transmission requester  280  outputs the equalization correction signal (con 2 ) to equalization controller  240  so that equalization controller  240  may adjust the equalization control signal (eq_con). In response to the changed equalization control signal (eq_con), the equalization characteristics of receiving equalizer  230  are controlled so that data may be received without error. 
         [0057]    In another embodiment, the pre-emphasis correction signal (con 1 ) may be output from re-transmission determiner  190  of transmission unit  100  instead of outputting the equalization correction signal (con 2 ) from re-transmission requester  280  of receiving unit  200 . In this case, re-transmission determiner  190  of transmission unit  100  outputs the pre-emphasis correction signal (con 1 ) so that pre-emphasis controller  170  may change the pre-emphasis control signal (pre_con). Thus, the pre-emphasis characteristics applied by pre-emphasis driver  160  may be controlled so that data is transmitted without error. 
         [0058]    Although both the pre-emphasis correction signal (con 1 ) and the equalization correction signal (con 2 ) may be output at the same time, only one of them is normally output because simultaneously altering more than one feedback loop variable may result in data errors unrelated to a control signal variation. Thus, when a data transmitting and receiving system is implemented with a re-transmission determiner  190  and a re-transmission requester  280  capable of outputting their respective correction signals (con 1  and con 2 ), only one of these circuits is typically enabled at any given point in time relative to the generation of a correction signal. 
         [0059]    Therefore, a data transmitting and receiving system such as the one shown in  FIG. 2  is capable of re-transmitting data a predetermined number of times when there is an error in data transmission, and is further capable of preventing errors from occurring in the data transmission by correcting a pre-emphasis coefficient in transmission unit  100  or an equalization coefficient in receiving unit  200  when systemic errors are repeatedly detected. Assuming as is typical that the data transmitting and receiving system has been initialized in relation to the anticipated channel conditions, it will only necessary to minimally correct the pre-emphasis coefficient or the equalization coefficient. 
         [0060]      FIGS. 3A and 3B  are circuit diagrams further illustrating the output driver shown in  FIG. 2 . 
         [0061]    As noted, output driver  140  of  FIG. 2  may includes transmission driver  150  and pre-emphasis driver  160 . In  FIG. 3A , a transmission driver  151  includes two NMOS transistors N 1  and N 2  as differential amplifiers. Thus, the NMOS transistors N 1  and N 2  differentially receive and amplify the differential output data (do and doB), respectively, and output the amplified data. Two resistors R 1  and R 2 , which are connected to a power supply voltage Vcc, are loads used for impedance-matching. Typically, each of the resistors R 1  and R 2  has a defined resistance of (e.g.,) 50Ω. Also, a constant current source CC 1  is connected to a ground voltage Vss and keeps the driving capability of the transmission driver  150  constant. Here, the constant current source CC 1  is typically embodied by an NMOS transistor having a gate terminal to which a constant voltage is applied. 
         [0062]    A pre-emphasis driver  161  of  FIG. 3A  has almost the same configuration as transmission driver  151 . However, pre-emphasis driver  161  does not include a load for impedance-matching unlike transmission driver  151 . In addition, pre-emphasis driver  161  does not receive the power supply voltage Vcc but is connected to an output signal of transmission driver  151  so that pre-emphasis driver  161  changes the output signals of transmission driver  151  and the output data signals (DO and DOB). Transmission driver  151  receives the differential output data (do and doB) as input signals, and pre-emphasis driver  161  receives, as input signals, delayed differential output data (ddo and ddoB) obtained by delaying the previous differential output data (do and doB) by a predetermined amount of time. Also, a variable current source VC 1  is connected to the common ground voltage Vss so as to control the driving capability of pre-emphasis driver  161 . The variable current source VC 1  controls the amount of current in response to the pre-emphasis control signal “pre_con” output from pre-emphasis controller  170  and may be embodied by a plurality of NMOS transistors. In other words, the NMOS transistors of the variable current source VC 1  have gate terminals to which respective bits of the pre-emphasis control signal “pre_con” are applied, and are enabled in response to the pre-emphasis control signal “pre_con” to control current supplied to the ground voltage Vss. 
         [0063]    Therefore, in output driver  140  of  FIG. 3A , when transmission driver  151  outputs output signals which are impedance-matched and amplified in response to the differential output data (do and doB), pre-emphasis driver  161  pre-emphasizes the output signals of transmission driver  151  and transmits output data signals (DO and DOB). 
         [0064]      FIG. 3B  illustrates another example of output driver  140  receiving only one data stream (i.e., a single output data—(do)) unlike output driver  140  of  FIG. 3A  which receives the differential output data (do and doB). A typical data transmitting and receiving system differentially transmits and receives data to enhance the accuracy of signals, but it is obvious that transmission unit  100  may output single data as well as differential data. When single data is output, two channels Ch and ChB need not be provided between transmission unit  100  and receiving unit  200 , but (under the working assumptions illustrated above) only a single channel Ch is required, along with return channel ChR. 
         [0065]    A transmission driver  152  of  FIG. 3B  is an inverter, which receives the single output data (do) as an input signal, inverts the output data (do), and outputs the inverted data. 
         [0066]    A pre-emphasis driver  162  of  FIG. 3B  includes a first plurality of inverters (inv 11  through inv 1   n ), each of which receives and inverts the single output data (do), transfer portions (HP 1 , through HPn) which are enabled in response to pre-emphasis control signals (pre_con 1  through pre_conn) output from pre-emphasis controller  170 , delay the inverted single output data (do) by respectively different predetermined amounts of time, control the voltage levels of the delayed data, and output the data of which voltage levels are controlled. Pre-emphasis driver  162  also includes a second plurality of inverters (inv 21  through inv 2   n ), which receive the signals output from the transfer portions (HP 1  through HPn) and output the signals at respectively different levels. The single output data (do) is output as output signals that are controlled to respectively different levels and delayed by respectively different predetermined amounts of time. Therefore, when transmission driver  152  receives the next single output data (do) and outputs the output signal, pre-emphasis driver  162  combines the output signals of second inverters (inv 21  through inv 2   n ) and outputs a pre-emphasized output data signal (DOB). Since the output data signal (DOB) is obtained by inverting and pre-emphasizing a single output data (do), receiving unit  200  must invert distorted data signal (DIB) received through channel “Ch”. 
         [0067]      FIGS. 4A and 4B  are block diagrams illustrating the possible implementations and corresponding operation of an equalizer adapted for use within embodiments of the invention. Typically, a feed forward equalizer (FFE) or a decision feedback equalizer (DFE) may be used as the equalizer.  FIG. 4A  illustrates an FFE including a plurality of transfer portions (HF 1  through HFn), which receive an input signal (Vin), delays the input signal (Vin) for predetermined amounts of time, and output the delayed signals at respectively different levels. The transfer portions (HF 1 , . . . , and HFn) output the signals at respectively different levels in response to the input signal (Vin) when the next input signal (Vin) is applied and allow a combiner add 1  to combine the output signals with the next input signal (Vin). In this case, the transfer portions (HF 1  through HFn) are selectively enabled to control the equalization intensity of the input signal (Vin). In other words, the next input signal (Vin) is equalized with reference to the previous input signal (Vin). 
         [0068]      FIG. 4B  illustrates a DFE, which includes a plurality of transfer portions (HD 1  through HDn) and a level determiner DM. When an input signal (Vin) #  is applied to the DFE, the level determiner DM determines the level of the input signal (Vin) and outputs an output signal (Vout) at a “high” or “low” level. Then, the transfer portions (HD 1  through HDn) receive the output signal (Vout), delay the output signal (Vout) for predetermined amounts of time, and output the delayed signals at respectively different levels. The respective signals output from the transfer portions (HD 1  through HDn) are combined with the next input signal (Vin) by a combiner add 2  and applied to the level determiner DM. In other words, the next input signal (Vin) is equalized with reference to the previous output signal (Vout). 
         [0069]    The FFE operates at high speed, but makes it difficult to determine timing because it delays and outputs signals in an analog manner. In contrast, although the DFE operates at low speed by use of feedback, the DFE refers to an output signal (Vout) of which level is determined, so that it is resistant to noise. 
         [0070]      FIG. 5  is a block diagram of an input driver adapted for use with the embodiment of the invention shown in  FIG. 2 . In  FIG. 5 , an FFE is used as input driver  210  of  FIG. 2 . 
         [0071]    Input driver  210  includes a receiving driver  221  and a receiving equalizer  231  and has almost the same configuration as output driver  140  of  FIG. 3A . Distorted data signals (DI and DIB) are received from transmission unit  100  through channels Ch and ChB into receiving driver  221 . Receiving driver  221  includes two NMOS transistors N 5  and N 6  as differential amplifiers. Thus, the NMOS transistors N 5  and N 6  differentially receive and amplify the distorted data signals (DI and DIB) and output the amplified data. Like the resistors R 1  and R 2  of  FIG. 3A , two resistors R 3  and R 4 , which are connected to a power supply voltage Vcc, are loads used for impedance-matching. Typically, each of the resistors R 3  and R 4  has a resistance of 50Ω. Also, a constant current source CC 2  is connected to a ground voltage Vss and keeps the driving capability of receiving driver  221  constant. Here, the constant current source CC 2  is typically embodied by an NMOS transistor having a gate terminal to which a constant voltage is applied. 
         [0072]    Receiving equalizer  231  does not receive the power supply voltage Vcc but is connected to an output terminal of receiving driver  221  so that receiving equalizer  231  changes the output signals of receiving driver  221  and outputs differential input data (di and diB). Receiving driver  221  receive the distorted data signals (DI and DIB) as input signals, and receiving equalizer  231  receives, as input signals, delayed distorted data signals (dDI and dDIB) obtained by delaying the received distorted data signals (DI and DIB) by a predetermined amount of time. Also, a variable current source VC 2  is connected to a common ground voltage Vss so as to control the driving capability of receiving equalizer  231 . The variable current source VC 2  controls the amount of current in response to the equalization control signal (eq_con) output from equalization controller  240  and may be embodied by a plurality of NMOS transistors. In other words, the NMOS transistors of the variable current source VC 2  have gate terminals to which respective bits of the equalization control signal (eq_con) are applied, and are enabled in response to the equalization control signal (eq_con) to control current supplied to the ground voltage Vss. 
         [0073]    Therefore, within input driver  210  of  FIG. 5 , when receiving driver  221  amplifies the distorted data signals (DI and DIB) and performs impedance-matching of the amplified data, receiving equalizer  231  equalizes the output signals of receiving driver  221  and outputs the differential input data (di and diB). 
         [0074]    According to the present invention as described above, when bit errors are detected more than a predetermined number of times during communication of data, a data transmitting and receiving system may be adjusted to a more optimal state of operation by correcting a pre-emphasis coefficient in the transmission unit or an equalization coefficient in the receiving unit without interrupting its regular operation to run a specialized mode designed to optimize system performance. Therefore, a data transmitting and receiving system according to an embodiment of the invention may efficiently operated in real time without data loss. 
         [0075]    Exemplary embodiments of the invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the scope of the present invention as set forth in the following claims.