Abstract:
A phase detection circuit is configured to generate a phase detection signal by comparing a divided clock signal obtained by dividing a first clock signal to a second clock signal during a deactivation period of a control signal, and generate the phase detection signal by comparing the first and second clock signals during an activation period of the control signal.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119(a) to Korean application number 10-2012-0070726, filed on Jun. 29, 2012, in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates generally to a semiconductor circuit, and more particularly, to a phase detection circuit and a synchronization circuit using the same. 
     2. Related Art 
     A conventional synchronization circuit such as a phase locked loop (PLL) or delayed locked loop (DLL) determines whether a phase or delay time has been adjusted to a value within a desired range, or whether a delay lock or phase lock has been achieved, during a phase or delay time adjustment process. 
     The synchronization circuit may use a phase detection circuit to determine whether a delay lock or phase lock has been achieved. 
     The phase detection circuit compares a reference signal REFCLK to a comparison target signal FBCLK and generates a result signal PDOUT. 
       FIG. 1  is a waveform diagram to demonstrate a phase detection operation for the conventional synchronization circuit. 
     Referring to  FIG. 1 , when noise components such as jitter are contained in the reference signal REFCLK and the comparison target signal FBCLK, the phase detection circuit may output the result signal as an abnormal value. 
     When the phase detection circuit outputs the result signal PDOUT as an abnormal value, an operation error of the synchronization circuit may occur. 
     SUMMARY 
     A phase detection circuit capable of performing a stable operation regardless of noise and a synchronization circuit using the is same are described herein. 
     In an embodiment of the present invention, a phase detection circuit is configured to generate a phase detection signal by comparing a divided clock signal obtained by dividing a first clock signal to a second clock signal during a deactivation period of a control signal, and generate the phase detection signal by comparing the first and second clock signals during an activation period of the control signal. 
     In an embodiment of the present invention, a phase detection circuit includes: a division section configured to generate a divided clock signal by dividing a first clock signal; a multiplexing section configured to select and output the first clock signal or the divided clock signal in response to a control signal; and a detection section configured to compare the phase of the output signal of the multiplexing section to a second clock signal and generate a phase detection signal. 
     In an embodiment of the present invention, a synchronization circuit includes: a variable delay unit configured to generate a synchronization clock signal by delaying a reference clock signal by a varied delay time; a feedback clock signal generation unit configured to receive the synchronization clock signal and generate a feedback clock signal; a control unit configured to vary the delay time of the variable delay unit in response to a phase detection signal and generate a lock completion signal in response to the transition of the phase detection signal; and a phase detection unit configured to generate the phase detection signal by comparing either the reference clock signal or the divided reference clock signal to the feedback clock signal in response to the lock completion signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, aspects, and embodiments are described in conjunction with the attached drawings, in which: 
         FIG. 1  is a waveform diagram demonstrating a phase detection operation of a conventional synchronization circuit; 
         FIG. 2  is a block diagram of a synchronization circuit according to an embodiment of the present invention; 
         FIG. 3  is a block diagram of a phase detection unit of  FIG. 2 ; 
         FIG. 4  is a timing diagram demonstrating the operation of the phase detection circuit of  FIG. 3 ; 
         FIG. 5  is a circuit diagram illustrating the configuration of a lock state detector of  FIG. 2 ; and 
         FIGS. 6 and 7  are waveform diagrams demonstrating the operation of the lock state detector of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a phase detection circuit and a synchronization circuit using the same according to the present invention will be described below with reference to the accompanying drawings through various embodiments. 
     Referring to  FIG. 2 , a synchronization circuit  100  according to one embodiment of the present invention includes a variable delay unit  110 , a control unit  120 , a feedback clock signal generation unit  150 , and a phase detection unit  10 . 
     The feedback clock signal generation unit  150  includes a division section  130  and a replica delay section  140 . 
     The variable delay unit  110  has a varied delay time in response to the control of the control unit  120 , and is configured to delay a first clock signal, i.e., a reference clock signal REFCLK by the varied delay time and generate a synchronization clock signal DLLCLK. 
     The control unit  120  is configured to control the variable delay unit  110  in response to a phase detection signal PDOUT, and generate a lock completion signal LOCK_STATE in response to the transition of the phase detection signal PDOUT. 
     The control unit  120  for generating the lock completion signal LOCK_STATE in response to the transition of the phase detection signal PDOUT may include a lock state detector  121 . 
     The division section  130  is configured to divide the synchronization clock signal DLLCLK by two. 
     The replica delay section  140  includes a delay element to replicate a delay time of a specific signal path. 
     The specific signal path may include an internal signal path through which an external clock signal passes in a circuit using the synchronization circuit  100 , for example, a semiconductor memory circuit. 
     The phase detection unit  10  is configured to compare either the reference clock signal REFCLK or a signal obtained by dividing the reference clock signal REFCLK to a second clock signal, i.e., a feedback clock signal FBCLK in response to the lock completion signal LOCK_STATE and a reset signal RSTB and generate the phase detection signal PDOUT. 
     Referring to  FIG. 3 , the phase detection unit  10  includes a division section  11 , a first delay section  12 , a multiplexing section  13 , a second delay section  14 , and a detection section  15 . 
     The division section  11  is configured to divide the reference clock signal REFCLK by two and generate the divided clock signal REFCLK/2. 
     The first delay section  12  is configured to delay the reference clock signal REFCLK by a preset time and generate the delayed reference clock signal REFCLKD. 
     The multiplexing section  13  is configured to select either the divided clock signal REFCLK/2 or the delayed reference clock signal REFCLKD in response to the lock completion signal LOCK_STATE. 
     The lock completion signal LOCK_STATE may include a signal that defines whether the delay lock of a DLL or the phase lock of a PLL has been completed. 
     In an embodiment of the present invention, the lock completion signal LOCK_STATE is used as a signal for controlling the phase detection unit  10 . However, this is only an example, and a control signal provided from an external source instead of a DLL or PLL may be used. 
     The second delay section  14  is configured to delay a feedback clock signal FBCLK by a preset time and generate the delayed feedback clock signal FBCLKD. 
     The first delay section  12  may be configured as a dummy delay device to compensate for a delay time of a signal path passing through the division section  11 . 
     The second delay section  14  may be configured as a dummy delay device to compensate for a delay time of a signal path passing through the multiplexing section  13  and either the division section  11  or the first delay section  12 . 
     The detection section  15  is configured to compare the phase of the delayed feedback clock signal FBCLKD to the phase of an output signal of the multiplexing section  13  and generate the phase detection signal PDOUT. 
     The detection section  15  is configured to initialize the phase detection signal PDOUT in response to a reset signal RSTB. 
     The operation of the phase detection unit  10  according to an embodiment of the present invention will be described as follows. 
     The multiplexing section  13  selects the divided clock signal REFCLK/2 and provides the selected signal to the detection section  15 , when the lock completion signal LOCK_STATE is deactivated (for example, low level). 
     The multiplexing section  13  provides the delayed reference clock signal REFCLKD to the detection section  15 , when the lock completion signal LOCK_STATE is activated (for example, high level). 
     When the lock completion signal LOCK_STATE is deactivated, the detection section  15  outputs the phase detection signal PDOUT as a high level in the case where a rising edge of the feedback clock signal FBCLK substantially leads a rising edge of the divided clock signal REFCLK/2. 
     Actual input signals of the detection section  15  may include the output signals of the multiplexing section  13  and the second delay section  14 . However, since the first and second delay sections  12  and  14  are dummy delay devices to compensate for an internal time delay, it may be understood that the detection section  15  effectively compares either the reference clock signal REFCLK or the divided clock signal REFCLK/2 to the feedback clock signal FBCLK. 
     When the lock completion signal LOCK_STATE is activated, the detection section  15  outputs the phase detection signal PDOUT as a high level in the case where the rising edge of the feedback clock signal FBCLK substantially leads a rising edge of the clock signal REFCLK. 
     In an embodiment of the present invention, when the lock completion signal LOCK_STATE is deactivated, the divided clock signal REFCLK/ 2  is used. 
     Although noise components such as jitter are contained in the delayed reference clock signal REFCLKD and the delayed feedback clock signal FBCLKD as illustrated in  FIG. 4 , the phase detection circuit  10  may output the phase detection signal PDOUT as a normal is value. 
     Referring to  FIG. 5 , the locking state detection section  121  is configured to activate the lock completion signal LOCK_STATE in response to the transition of the phase detection signal PDOUT. 
     The locking state detection section  121  detects both the case in which the phase detection signal PDOUT transits from a high level to a low level and the case in which the phase detection signal PDOUT transits from a low level to a high level, and activates the lock completion signal LOCK_STATE. 
     The locking state detection section  121  includes a first flip-flop  122 , a second flip-flop  123 , and a logic gate  124 . 
     The first flip-flop  122  has an input terminal connected to a power supply terminal and a clock terminal configured to receive the inverted phase detection signal PDOUT. 
     The second flip-flop  123  has an input terminal connected to the power supply terminal and a clock terminal configured to receive the phase detection signal PDOUT. 
     The first and second flip-flops  122  and  123  are reset by a reset signal RSTB. 
     The logic gate  124  is configured to perform an OR operation on output signals of the first and second flip-flops  122  and  123  and output the lock completion signal LOCK_STATE. 
     The operation of the synchronization circuit  100  according to an embodiment of the present invention will be described as follows. 
     The phase detection unit  10  compares the phase of the divided clock signal REFCLK/2 to the phase of the feedback clock signal FBCLK and generates the phase detection signal PDOUT, when the lock completion signal LOCK_STATE is deactivated (for example, low level). 
     The control unit  120  increases or decreases the delay time of the variable delay unit  110  according to the level of the phase detection signal PDOUT. 
     The phase of the feedback clock signal FBCLK changes in response to the increase or decrease in delay time of the variable delay unit  110 . 
     When the phase of the feedback clock signal FBCLK changes in response to the delay time depicted as FBCLKD in  FIG. 6  in a state where the phase of the divided clock signal REFCLK/2 is locked, the phase detection signal PDOUT transits from a high level to a low level. 
     As the phase detection signal PDOUT transits from a high level to a low level, the first flip-flop  122  of  FIG. 5  outputs a power supply level, i.e., a high level signal. 
     As the high level signal outputted from the first flip-flop  122  is outputted through the logic gate  124 , the lock completion signal LOCK_STATE is activated. 
     When the phase of the feedback clock signal FBCLK changes in response to the delay time depicted as FBCLKD in  FIG. 7  in a state where the phase of the divided clock signal REFCLK/2 is locked, the phase detection signal PDOUT transits from a low level to a high level. 
     As the phase detection signal PDOUT transits from a low level to a high level, the second flip-flop  123  of  FIG. 5  outputs a power supply level, i.e., a high level signal. 
     As the high level signal outputted from the second flip-flop  123  is outputted through the logic gate  124 , the lock completion signal LOCK_STATE is activated. 
     When the lock completion signal LOCK_STATE is activated, the phase detection unit  10  compares the phase of the reference clock signal REFCLK to the phase of the feedback clock signal FBCLK and generates the phase detection signal PDOUT. 
     The control unit  120  increases or decreases the delay time of the variable delay unit  110  according to the level of the phase detection signal PDOUT. 
     After the lock completion signal LOCK_STATE is activated, the delay time of the variable delay unit  110  is minutely adjusted. 
     The phase of the feedback clock signal FBCLK also changes in response to the increase or decrease in delay time of the variable delay unit  110 . 
     In an embodiment of the present invention, the feedback clock signal FBCLK is compared to the divided clock signal REFCLK/2 before the lock completion state, i.e., before the lock completion signal LOCK_STATE is activated, and compared to the reference clock signal REFCLK after the lock completion signal LOCK_STATE is activated, allowing for a stable phase detection. 
     Although a time point when the phase detection signal PDOUT transits to a specific level is not detected, because the transition of the phase detection signal PDOUT to a low level and a high level is determined as the lock completion, it is possible to guarantee a stable operation of the synchronization circuit. 
     While certain embodiments have been described above, it will be understood to those skilled in the art that the embodiments described are by way of example only. Accordingly, the semiconductor circuit described herein should not be limited based on the described embodiments. Rather, the semiconductor circuit described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.