Patent Publication Number: US-11641267-B2

Title: Clock and data recovery circuit and source driver including the same

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a display apparatus, and more particularly, to a clock and data recovery circuit capable of easily recovering a clock and data in a high-speed operation and a source driver including the same. 
     2. Related Art 
     In general, a display apparatus may include a display panel, a source driver, a timing controller, etc. 
     The source driver converts image data, provided by the timing controller, into a data voltage and provides the data voltage to the display panel. The source driver may be integrated in the form of a chip, and may be configured in plural in the display panel by considering the size and resolution of a screen. 
     The source driver may include a clock and data recovery circuit for recovering a clock signal and data. The clock and data recovery circuit is for receiving, from the timing controller, an input signal in which a clock has been embedded in data and recovering a clock signal and data from the input signal. 
     A common clock and data recovery circuit may include a bang-bang phase detector, and may control the phase of a clock signal by using the bang-bang phase detector. 
     However, if the common clock and data recovery circuit recovers data transmitted at a high speed, a jitter characteristic of the bang-bang phase detector may deteriorate. Furthermore, the common clock and data recovery circuit has problems in that the circuit is complicated due to the mixture of a digital circuit and an analog circuit and a chip area is increased due to a passive element. 
     SUMMARY 
     Various embodiments are directed to providing a clock and data recovery circuit capable of easily recovering a clock signal and data in a high-speed operation and a source driver including the same. 
     In an embodiment, a clock and data recovery circuit may include a clock recovery unit configured to perform first time-to-digital conversion or second time-to-digital conversion on a first phase difference between a clock of an input signal and a recovery clock signal depending on whether the first phase difference is greater than a preset reference phase difference and to output the recovery clock signal, a first clock signal and a second clock signal corresponding to the first time-to-digital conversion or the second time-to-digital conversion, wherein a second phase difference between the first clock signal and the recovery clock signal is different from a third phase difference between the second clock signal and the recovery clock signal, and a data recovery unit configured to sample data from the input signal by using the first clock signal and the second clock signal and output recovery data. 
     In an embodiment, a source driver may include a clock and data recovery circuit configured to generate a recovery clock signal and recovery data from an input signal, and a data driving circuit configured to generate a data voltage by using the recovery clock signal and the recovery data and provide the data voltage to a display panel. The clock and data recovery circuit may include a first time-to-digital conversion circuit configured to receive the input signal having a clock training pattern and output a first digital signal corresponding to a first phase difference between a clock of the input signal and the recovery clock signal, a second time-to-digital conversion circuit configured to receive the input signal in which a clock has been embedded in data and output a second digital signal corresponding to the first phase difference, a digital loop filter configured to output a control signal corresponding to the first digital signal or the second digital signal, and a digitally controlled oscillator configured to output the recovery clock signal, a first clock signal and a second clock signal having phases controlled in response to the control signal, wherein a second phase difference between the first clock signal and the recovery clock signal is different from a third phase difference between the second clock signal and the recovery clock signal. 
     According to embodiments, a clock signal and data can be easily recovered even in an operation of recovering data transmitted at a high speed because the time-to-digital conversion circuit capable of comparing a clock of an input signal and a recovery clock signal is used. 
     Furthermore, according to embodiments, a circuit for recovering a clock signal and data is implemented using a digital circuit. Therefore, the configuration thereof can be simplified and scalability for a process change can be facilitated. 
     Furthermore, according to embodiments, a clock embedded in data can be easily recovered because a clock of an input signal and a recovery clock signal can be compared although a location of the clock is changed depending on a protocol of the input signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of a clock and data recovery circuit according to an embodiment. 
         FIG.  2    is a flowchart for describing an operation of the clock and data recovery circuit according to an embodiment. 
         FIG.  3    is a circuit diagram of a sampler illustrated in  FIG.  1   . 
         FIG.  4    is a block diagram illustrating an example of a time-to-digital conversion circuit. 
         FIG.  5    is a block diagram of a second time-to-digital conversion circuit illustrated in  FIG.  4   . 
         FIG.  6    illustrates a timing diagram of a clock of an input signal and a recovery clock signal. 
         FIG.  7    illustrates a timing diagram of a comparison between phases of a recovery clock signal and a first clock signal having a phase difference of 0.5 UI with respect to the recovery clock signal. 
         FIG.  8    is a flowchart for describing an operation of the second time-to-digital conversion circuit illustrated in  FIG.  5   . 
         FIG.  9    is a circuit diagram of a flip-flop array illustrated in  FIG.  5   . 
         FIG.  10    is a circuit diagram illustrating a time-to-digital converter. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments may provide a clock and data recovery circuit capable of easily recovering a clock and data in a high-speed operation, and a source driver including the same. 
     Embodiments may provide a time-to-digital conversion circuit for a clock and data recovery circuit, and a source driver including the same. 
     An input signal is provided to have a clock training pattern in the early stage of an operation and then to have data in which a clock has been embedded. The clock training pattern means a clock pattern including a clock for recovery. The input signal having the clock training pattern may be provided to stabilize a clock signal in a clock training period set in the early stage of an operation, etc. 
     In embodiments, it may be understood that the clock and data recovery circuit may receive an input signal having a clock training pattern in the early stage of an operation, and the clock and data recovery circuit compares a recovery clock signal and a clock of the input signal and receives the input signal having data in which a clock has been embedded after a coarse lock stabilized within a preset range. Image data and control data may be included in the data. 
     The coarse lock may be enabled when a time difference between a clock of an input signal and a recovery clock signal is equal to or smaller than a reference time, and may be disabled when the time difference between the clock of the input signal and the recovery clock signal is greater than the reference time. In this case, the recovery clock signal may be defined as a clock signal recovered using the clock of the input signal. 
     As described above, the time difference means a phase difference between a clock of the input signal and the recovery clock signal. Hereinafter, it may be understood that a phase difference corresponds to the time difference. A reference time difference may be understood as a reference phase difference. For example, assuming that one cycle of a recovery clock signal includes two unit intervals (2 UI) and the duty ratio of the recovery clock signal is 50:50, in an embodiment of the present disclosure, the reference phase difference may be set to 0.5 UI. It may be understood that the reference phase difference of 0.5 UI corresponds to a phase difference of 90°. 
     Furthermore, it may be understood that the coarse lock is enabled when a phase difference between a clock of an input signal and a recovery clock signal is equal to or smaller than the reference phase difference of 0.5 UI, and is disabled when the phase difference between the clock of the input signal and the recovery clock signal is greater than the reference phase difference of 0.5 UI. 
     In embodiments, a coarse loop may be defined to align a clock of an input signal and a recovery clock signal so that the clock of the input signal and the recovery clock signal have a phase difference within a reference phase difference when the phase difference is greater than the reference phase difference. 
     In embodiments, a fine loop may be defined to align a clock of an input signal and a recovery clock signal so that the clock of the input signal and the recovery clock signal have a more reduced phase difference within a reference phase difference when the phase difference is equal to or smaller than the reference phase difference. 
     In embodiments, terms, such as a first and a second, may be used to distinguish between various elements. The elements are not limited by terms, such as a first and a second. 
       FIG.  1    is a block diagram of a clock and data recovery circuit  100  according to an embodiment. 
     The clock and data recovery circuit  100  may include a clock recovery unit  110  and a data recovery unit  120 . 
     The clock recovery unit  110  is configured to perform first time-to-digital conversion or second time-to-digital conversion on a phase difference between a clock of an input signal DIN and a recovery clock signal depending on whether the phase difference is greater than a preset reference phase difference. 
     Furthermore, the clock recovery unit  110  is configured to output a recovery clock signal, a first clock signal and a second clock signal corresponding to the first time-to-digital conversion or the second time-to-digital conversion. In this case, it is preferred that a phase difference between the first clock signal and the recovery clock signal is different from that between the second clock signal and the recovery clock signal. 
     Furthermore, the data recovery unit  120  is configured to sample data from the input signal DIN by using the first clock signal and the second clock signal and to output recovered data R_DATA. 
     The clock recovery unit  110  may receive the input signal DIN, and may generate a recovery clock signal corresponding to a phase of the clock of the input signal DIN, the first clock signal having a phase difference of 0.5 UI from the recovery clock signal, and the second clock signal having a phase difference of 1.5 UI from the recovery clock signal. For a description of an embodiment, the recovery clock signal is indicated as CK 0 °, the first clock signal is indicated as CK 90 °, and the second clock signal is indicated as CK 270 °. 
     The clock recovery unit  110  may include a first time-to-digital conversion circuit CTDC for the first time-to-digital conversion and a second time-to-digital conversion circuit DTDC for the second time-to-digital conversion. The first time-to-digital conversion circuit CTDC and the second time-to-digital conversion circuit DTDC may operate so that the first time-to-digital conversion circuit CTDC and the second time-to-digital conversion circuit DTDC are alternately enabled and disabled in response to a coarse lock signal C_LOCK. 
     For example, a level of the coarse lock signal C_LOCK may transition to a low logic level for coarse lock disabling when a phase difference between a clock of the input signal DIN and a recovery clock signal is greater than the reference phase difference of 0.5 UI. In this case, the first time-to-digital conversion circuit CTDC is enabled, and the second time-to-digital conversion circuit DTDC is disabled. 
     Furthermore, a level of the coarse lock signal C_LOCK may shift to a high logic level for coarse lock enabling when a phase difference between a clock of the input signal DIN and a recovery clock signal is equal to or smaller than the reference phase difference of 0.5 UI. In this case, the first time-to-digital conversion circuit CTDC is disabled, and the second time-to-digital conversion circuit DTDC is enabled. 
     The clock recovery unit  110  may output the recovery clock signal CK 0 °, the first clock signal CK 90 ° and the second clock signal CK 270 ° having oscillation frequencies and phases controlled by using a first digital signal COUT of the first time-to-digital conversion circuit CTDC or a second digital signal DOUT of the second time-to-digital conversion circuit DTDC. 
     In this case, the recovery clock signal CK 0 ° may be fed back to the first time-to-digital conversion circuit CTDC and the second time-to-digital conversion circuit DTDC. Furthermore, the first clock signal CK 90 ° may be fed back to the second time-to-digital conversion circuit DTDC. The fed-back recovery clock signal CK 0 ° and the fed-back first clock signal CK 90 ° may be used to align the phases of a clock of the input signal DIN and the recovery clock signal CK 0 °. 
     The first clock signal CK 90 ° and the second clock signal CK 270 ° may be provided to the data recovery unit  120 , and may be used to recover data from the input signal DIN. 
     The clock recovery unit  110  may include the first time-to-digital conversion circuit CTDC, the second time-to-digital conversion circuit DTDC, a digital loop filter  40 , a digitally controlled oscillator  50  and a clock divider  30 . 
     The first time-to-digital conversion circuit CTDC may receive the input signal DIN from a timing controller, and may output the first digital signal COUT corresponding to a phase difference between a clock of the input signal DIN and a recovery clock signal. The timing controller may transmit the input signal DIN including a clock training pattern in the early stage of an operation. 
     The first time-to-digital conversion circuit CTDC may be used as a coarse loop for aligning a clock of the input signal DIN and the recovery clock signal CK 0 ° when a phase difference between the clock of the input signal DIN and the recovery clock signal CK 0 ° is greater than the reference phase difference of 0.5 UI. 
     The first time-to-digital conversion circuit CTDC may operate to reduce a phase difference between the clock of the input signal DIN and the recovery clock signal CK 0 ° within the reference phase difference of 0.5 UI through phase alignment, and may be disabled by the coarse lock signal C_LOCK when a phase difference between the clock of the input signal DIN and the recovery clock signal CK 0 ° is equal to or smaller than the reference phase difference of 0.5 UI. 
     The second time-to-digital conversion circuit DTDC may be enabled by the coarse lock signal C_LOCK when a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° is equal to or smaller than the reference phase difference of 0.5 UI by the first time-to-digital conversion circuit CTDC. 
     The second time-to-digital conversion circuit DTDC may receive, from the timing controller, the input signal DIN having data in which a clock has been embedded, and may output the second digital signal DOUT corresponding to a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 °. 
     The second time-to-digital conversion circuit DTDC may be used as a fine loop for aligning a clock of the input signal DIN and the recovery clock signal CK 0 ° so that the clock of the input signal DIN and the recovery clock signal CK 0 ° have a more reduced phase difference within the reference phase difference of 0.5 UI. 
     The second time-to-digital conversion circuit DTDC may be disabled by the coarse lock signal C_LOCK, or may output the second digital signal DOUT that maintains a previous value when a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° is greater than the reference phase difference of 0.5 UI or the clock is not recognized in the input signal DIN. A case where a clock is not recognized in the input signal DIN may correspond to a case where consecutive data maintains logical “0” and a shift for a clock does not occur. 
     The second time-to-digital conversion circuit DTDC may receive the recovery clock signal CK 0 ° and the first clock signal CK 90 ° from the digitally controlled oscillator  50 , and may output the second digital signal DOUT when a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° is equal to or smaller than a phase difference between the recovery clock signal CK 0 ° and the first clock signal CK 90 °. 
     When a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° is greater than a phase difference between the recovery clock signal CK 0 ° and the first clock signal CK 90 °, the second time-to-digital conversion circuit DTDC may output the second digital signal DOUT that maintains a previous value. This corresponds to a case where the phase difference between the clock of the input signal DIN and the recovery clock signal CK 0 ° is greater than the reference phase difference of 0.5 UI. 
     The digital loop filter  40  may convert the first digital signal COUT or the second digital signal DOUT into a control signal VCON having an input range in which the digitally controlled oscillator  50  may operate, and may provide the control signal VCON to the digitally controlled oscillator  50 . 
     The digitally controlled oscillator  50  may generate the recovery clock signal CK 0 °, the first clock signal CK 90 ° and the second clock signal CK 270 ° having different phases by controlling an oscillation frequency and a phase in response to the control signal VCON. 
     The clock divider  30  may provide the first time-to-digital conversion circuit CTDC with a division clock signal obtained by dividing the recovery clock signal CK 0 ° by a division ratio N. In this case, N is a natural number, and a value of N may be determined depending on a protocol configured between the timing controller and a source driver. The clock divider  30  may raise an output frequency and lower a comparison frequency. 
     The first time-to-digital conversion circuit CTDC may output the first digital signal COUT corresponding to a phase difference between a clock of the input signal and the division clock signal. 
     The data recovery unit  120  may sample image data from the input signal DIN by using the first clock signal CK 90 ° and the second clock signal CK 270 °, and may provide the recovered image data R_DATA to a data driving circuit  130 . The data driving circuit  130  may convert the recovered image data R_DATA into a data voltage and provide the data voltage to a display panel. 
     The data recovery unit  120  may include a sampler  10  and a serial-to-parallel circuit  20 . 
     The sampler  10  may receive the input signal DIN, may sample odd-numbered data DATA_ODD in response to the first clock signal CK 90 °, and may sample even-numbered data DATA_EVEN in response to the second clock signal CK 270 °. 
     The serial-to-parallel circuit  20  may convert serial odd-numbered data DATA_ODD and serial even-numbered data DATA_EVEN into parallel data and output the parallel data as the recovered image data R_DATA in response to the first clock signal CK 90 ° and the second clock signal CK 270 °, respectively. 
     The source driver may include the clock and data recovery circuit  100  and the data driving circuit  130 . 
     The source driver may receive, from the timing controller, the input signal DIN having a clock training pattern or having data in which a clock has been embedded. 
     In this case, the clock and data recovery circuit  100  may recover a clock signal and data from the input signal DIN, and may provide a clock signal and data to the data driving circuit  130 . 
     The data driving circuit  130  may convert image data into a data voltage and provide the data voltage to the display panel. 
       FIG.  2    is a flowchart for describing an operation of the clock and data recovery circuit  100  according to an embodiment. 
     First, when power is on, a value of the division ratio N of the clock divider  30  may be determined according to a preset protocol (S 10 ). 
     The first time-to-digital conversion circuit CTDC may receive the input signal DIN having a clock training pattern in the early stage of an operation (S 20 ). 
     Furthermore, the recovery clock signal CK 0 ° of the digitally controlled oscillator  50  may be input to the first time-to-digital conversion circuit CTDC (S 30 ). In this case, the recovery clock signal CK 0 ° may be a division clock signal divided by the clock divider  30 , and may be input to the first time-to-digital conversion circuit CTDC. 
     The first time-to-digital conversion circuit CTDC may operate as a coarse loop for phase alignment. 
     The first time-to-digital conversion circuit CTDC compares a clock of the input signal DIN and the recovery clock signal CK 0 ° input in the form of a division clock signal (S 30 ). 
     A coarse lock may occur in the first time-to-digital conversion circuit CTDC when a phase difference between the recovery clock signal CK 0 ° and the clock of the input signal DIN is equal to or smaller than the reference phase difference of 0.5 UI (S 35 ). In this case, the occurrence of the coarse lock means the enabling of the coarse lock. A level of the coarse lock signal C_LOCK shifts to a high logic level. 
     Furthermore, when the coarse lock occurs, the first time-to-digital conversion circuit CTDC may be disabled and an operation thereof may be stopped, and a value of the first digital signal COUT of the first time-to-digital conversion circuit CTDC may be fixed. In conjunction with the operation of the first time-to-digital conversion circuit CTDC, the second time-to-digital conversion circuit DTDC may be enabled and operate (S 40 ). 
     More specifically, the first time-to-digital conversion circuit CTDC may be disabled when a phase difference between the clock of the input signal DIN and the recovery clock signal CK 0 ° is equal to or smaller than the reference phase difference of 0.5 UI through phase alignment. In this case, the second time-to-digital conversion circuit DTDC may be enabled. 
     Furthermore, the second time-to-digital conversion circuit DTDC may receive the input signal DIN having data in which a clock has been embedded (S 50 ). 
     The second time-to-digital conversion circuit DTDC compares a clock of the input signal DIN and the recovery clock signal CK 0 ° (S 60 ). 
     When a phase difference between the clock of the input signal DIN and the recovery clock signal CK 0 ° is equal to or smaller than the reference phase difference of 0.5 UI, the second time-to-digital conversion circuit DTDC may convert the phase difference into the second digital signal DOUT (S 70 ). 
     In this case, when the phase difference between the clock of the input signal DIN and the recovery clock signal CK 0 ° is greater than the reference phase difference of 0.5 UI, the second time-to-digital conversion circuit DTDC may output the second digital signal DOUT that maintains a previous value (S 70 ). 
     Furthermore, when the clock is not recognized in the input signal DIN, the second time-to-digital conversion circuit DTDC may output the second digital signal DOUT that maintains a previous value. 
     Furthermore, the sampler  10  may sample the odd-numbered data DATA_ODD in response to the first clock signal CK 90 °, and may sample the even-numbered data DATA_EVEN in response to the second clock signal CK 270 ° (S 80 ). 
     Furthermore, the serial-to-parallel circuit  20  may convert serial odd-numbered data DATA_ODD and serial even-numbered data DATA_EVEN into parallel data in response to the first clock signal CK 90 ° and the second clock signal CK 270 °, respectively, and may output the recovered image data R_DATA (S 90 ). 
       FIG.  3    is a circuit diagram of the sampler  10  illustrated in  FIG.  1   . 
     The sampler  10  may include a first D flip-flop (D-FF)  12  and a second D flip-flop (D-FF)  14 . 
     The first D flip-flop  12  may receive the input signal DIN having data in which a clock has been embedded, and may output odd-numbered data DATA_ODD of the input signal DIN in response to the first clock signal CK 90 °. 
     The second D flip-flop  14  may receive the input signal DIN having data in which a clock has been embedded, and may output even-numbered data DATA_EVEN of the input signal DIN in response to the second clock signal CK 270 °. 
       FIG.  4    is a block diagram of a time-to-digital conversion circuit  35  for the clock and data recovery circuit  100  according to an embodiment. 
     The time-to-digital conversion circuit  35  may include the first time-to-digital conversion circuit CTDC, the second time-to-digital conversion circuit DTDC and a multiplexer  42 . 
     Operations of the first time-to-digital conversion circuit CTDC and the second time-to-digital conversion circuit DTDC of  FIG.  4    may be understood with reference to  FIG.  1   , and a detailed description thereof is omitted. 
     The multiplexer  42  may be configured to select the first digital signal COUT when the coarse lock signal C_LOCK is disabled, to select the second digital signal DOUT when the coarse lock signal C_LOCK is enabled, and to output, as a digital signal SOUT, the selected digital signal to the digital loop filter  40 . 
     The time-to-digital conversion circuit  35  of  FIG.  4    is illustrated as including the multiplexer  42 . For another example, the multiplexer  42  may be included in the digital loop filter  40  of  FIG.  1   . 
       FIG.  5    is a block diagram of the second time-to-digital conversion circuit DTDC illustrated in  FIG.  4   . 
     The second time-to-digital conversion circuit DTDC may include a first time-to-digital converter TDC 1 , a second time-to-digital converter TDC 2 , a comparator  60 , a flip-flop array  70  and an encoder  80 . 
     The first time-to-digital converter TDC 1  may output a digital value corresponding to a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 °, that is, a first output signal OUT 1 . 
     The second time-to-digital converter TDC 2  may output a digital value corresponding to a phase difference between the recovery clock signal CK 0 ° and the first clock signal CK 90 °, that is, a second output signal OUT 2 . 
     The comparator  60  may compare values of the first output signal OUT 1  and the second output signal OUT 2 , and may output a digital value based on a result of the comparison, that is, a comparison signal COMP. 
     For example, the comparator  60  may output an enabled comparison signal COMP when a value of the first output signal OUT 1 , that is, a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° is equal to or smaller than a value of the second output signal OUT 2 , that is, a phase difference between the recovery clock signal CK 0 ° and the first clock signal CK 90 °. 
     The flip-flop array  70  may update and store the first output signal OUT 1  in response to the enabled comparison signal COMP, and may output an updated value as a flip-flop signal FOUT in response to a disabled comparison signal COMP or may output the flip-flop signal FOUT that maintains a previous value without an update. 
     For example, when a value of the first output signal OUT 1  is equal to or smaller than a value of the second output signal OUT 2 , the flip-flop array  70  may output an n-th first output signal OUT 1  as an n-th flip-flop signal FOUT in response to the enabled comparison signal COMP. 
     In contrast, when a value of the first output signal OUT 1  is greater than a value of the second output signal OUT 2 , the flip-flop array  70  may maintain an (n−1)-th first output signal OUT 1  and output the (n−1)-th first output signal OUT 1  as an n-th flip-flop signal FOUT in response to the disabled comparison signal COMP. 
     The encoder  80  may convert the flip-flop signal FOUT into the second digital signal DOUT. 
     As a result, the encoder  80  may convert, into the second digital signal DOUT, the flip-flop signal FOUT corresponding to a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 °. 
     As described above, when a value of the first output signal OUT 1  is equal to or smaller than a value of the second output signal OUT 2 , the second time-to-digital conversion circuit DTDC may convert the first output signal OUT 1  into the second digital signal DOUT. 
     Furthermore, when a value of the first output signal OUT 1  is greater than a value of the second output signal OUT 2 , the second time-to-digital conversion circuit DTDC may output the second digital signal DOUT that maintains a previous value. 
     For example, when a value of an n-th first output signal OUT 1  is greater than a value of the second output signal OUT 2 , the second time-to-digital conversion circuit DTDC may output an n-th second digital signal DOUT that maintains a value of an (n−1)-th second digital signal DOUT. 
     Furthermore, when a clock is not recognized in the input signal DIN, the second time-to-digital conversion circuit DTDC may output the second digital signal DOUT that maintains a previous value. 
       FIG.  6    illustrates a timing diagram of a clock of the input signal DIN and the recovery clock signal CK 0 °. 
     Referring to  FIG.  6   , a clock of the input signal DIN may be periodically input. Phases of a clock of the input signal DIN and the recovery clock signal CK 0 ° may be aligned through a coarse loop operation of the first time-to-digital conversion circuit CTDC and a fine loop operation of the second time-to-digital conversion circuit DTDC. 
     In this case, when a clock is not recognized in the input signal DIN, the time-to-digital conversion circuit  35  may maintain a previous value of the second digital signal DOUT so that the coarse loop operation or the fine loop operation is not performed. 
     For example, when a clock is not recognized in an n-th input signal DIN, the time-to-digital conversion circuit  35  may maintain a value of an n-th second digital signal DOUT as a value of an (n−1)-th second digital signal DOUT. 
     This is for preventing an output of the digitally controlled oscillator  50  from being changed because an output of the time-to-digital conversion circuit  35  becomes a maximum when a difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° is not determined. 
       FIG.  7    illustrates a timing diagram of the recovery clock signal CK 0 ° and the first clock signal CK 90 °. 
       FIG.  7    illustrates that a phase difference between the recovery clock signal CK 0 ° and the first clock signal CK 90 ° is set as a reference phase difference of 0.5 UI. 
     The second time-to-digital conversion circuit DTDC may compare a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° and a fixed phase difference between the recovery clock signal CK 0 ° and the first clock signal CK 90 ° as illustrated in  FIG.  7   . 
       FIG.  8    is a flowchart for describing an operation of the time-to-digital conversion circuit  35  of  FIG.  5   . 
     Referring to  FIG.  8   , when a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° is equal to or smaller than the reference phase difference of 0.5 UI, the second time-to-digital conversion circuit DTDC may operate (S 11 ). 
     The second time-to-digital converter TDC 2  may convert, into a digital value, the reference phase difference of 0.5 UI corresponding to a phase difference between the recovery clock signal CK 0 ° and the first clock signal CK 90 °, and may output the digital value as the second output signal OUT 2  (S 12 ). 
     The first time-to-digital converter TDC 1  may convert, into a digital value, a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 °, and may output the digital value as the first output signal OUT 1  (S 13 ). 
     The comparator  60  may compare values of the first output signal OUT 1  and the second output signal OUT 2 , and may output the comparison signal COMP based on a result of the comparison (S 14 ). 
     When the value of the first output signal OUT 1  is equal to or smaller than the value of the second output signal OUT 2 , the comparator  60  may output the comparison signal COMP in an enable state, that is, at a high logic level. When the value of the first output signal OUT 1  is greater than the value of the second output signal OUT 2 , the comparator  60  may output the comparison signal COMP in a disable state, that is, at a low logic level. 
     The flip-flop array  70  may update the first output signal OUT 1  and output an updated value as the flip-flop signal FOUT or may output the flip-flop signal FOUT that maintains a previous value, in response to the comparison signal COMP (S 15 ). 
     The encoder  80  may output the second digital signal DOUT obtained by converting the number of “H” in the flip-flop signal FOUT into a binary number (S 16 ). 
     As a result, the encoder  80  may convert a phase difference between a clock of the input signal DIN and the recovery clock signal CK 0 ° into the second digital signal DOUT. 
       FIG.  9    is a circuit diagram of the flip-flop array  70  illustrated in  FIG.  5   . 
     The flip-flop array  70  may include D flip-flops D-FF corresponding to an output signal OUT 1 [ 0 ] to an output signal OUT 1 [ n ], respectively. 
     The D flip-flops D-FF may update the output signals OUT 1 [ 0 ] to OUT 1 [ n ] and output updated flip-flop signals FOUT or may output the flip-flop signals FOUT that maintain previous values, respectively, in response to the comparison signal COMP. When a value of the first output signal OUT 1  is equal to or smaller than a value of the second output signal OUT 2 , a level of the comparison signal COMP may be input as a high logic level, so that the updates of the D flip-flops D-FF and the outputs of the flip-flop signals FOUT may be controlled. Furthermore, when a value of the first output signal OUT 1  is greater than a value of the second output signal OUT 2 , a level of the comparison signal COMP may be input as a low logic level, so that the maintenance of previous values of the D flip-flops D-FF and the outputs of the flip-flop signals FOUT may be controlled. 
       FIG.  10    is a circuit diagram of a time-to-digital converter TDC. 
     Referring to  FIG.  10   , the time-to-digital converter TDC may output output signals OUT[ 0 ] to OUT[n] corresponding to phase differences among signals, respectively, which are input to a reference terminal REF and a feedback terminal FEB. 
     For example, the time-to-digital converter TDC may output the output signals OUT[ 0 ] to OUT[n] as “HHHLLLLL . . . ” or “LLLHHHHH . . . ” according to which signal has an earlier phase among the signals input to the reference terminal REF and the feedback terminal FEB. 
     In this case, the number of “H” may be determined as “HHHLLLLL . . . ” in which H is sequentially positioned from the least significant bit (LSB). The encoder  80  may convert, into a binary number, bits corresponding to the number of “H.” 
     As described above, the clock and data recovery circuit and the source driver including the same according to the present embodiments can use the time-to-digital conversion circuit capable of comparing a clock of an input signal and a recovery clock signal, thereby easily recovering a clock and data even in an operation of transmitting data at a high speed. 
     Furthermore, according to embodiments, a circuit can be simplified and scalability for a process change can be facilitated because the circuit is implemented as a digital circuit. 
     Furthermore, according to embodiments, a clock embedded in data can be recovered because a clock signal and data can be compared although a location of the clock is changed depending on a protocol.