Abstract:
There is provided a phase detection apparatus that can accurately detect a phase difference between an input signal and a reference signal even when the input signal and the reference signal have different duty cycles. A phase detection apparatus according to an aspect of the invention may include: a pulse generation unit generating a first pulse signal on an edge of an input pulse signal, and a second pulse signal based on an edge of a reference pulse signal having a predetermined phase; and a detection unit detecting a phase difference between the first pulse signal and the second pulse signal from the pulse generation unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 2007-0087195 filed on Aug. 29, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to phase detection apparatuses, and more particularly, to a phase detection apparatus that can accurately detect a phase difference between an input signal and a reference signal even though the input signal and the reference signal have different duty cycles. 
   2. Description of the Related Art 
   Recently, liquid crystal display (LCD) products have come into widespread use because they are small, lightweight, and thin. Backlight units that supply light are used in the LCD products. The LCD products use lamp driving signals for controlling the driving of lamps in the backlight unit, and horizontal and vertical synchronization signals used for images of the LCD. 
   If interference occurs between the lamp driving signal and the horizontal and vertical synchronization signals that are used in the LCD product, the screen shakes, and that is called a “waterfall”. In order to prevent this waterfall on the screen, a phase detector is used to synchronize the signals used in the LCD product with a predetermined reference signal such that the interference between the lamp driving signal and the horizontal and vertical synchronization signals can be avoided. 
   However, according to the related art, when a phase detector detects a phase difference between an input signal and a reference signal, if the input signal and the reference signal have different duty cycles, the phase detector detects a phase difference corresponding to a duty-cycle difference between the input signal and the reference signal even through the input signal and the reference signal are synchronized with each other. 
   SUMMARY OF THE INVENTION 
   An aspect of the present invention provides a phase detection apparatus that can accurately detect a phase difference between an input signal and a reference signal even though the input signal and the reference signal have different duty cycles. 
   According to an aspect of the present invention, there is provided a phase detection apparatus including: a pulse generation unit generating a first pulse signal on an edge of an input pulse signal, and a second pulse signal based on an edge of a reference pulse signal having a predetermined phase; and a detection unit detecting a phase difference between the first pulse signal and the second pulse signal from the pulse generation unit. 
   The pulse generation unit may include: a first pulse generator generating the first pulse signal synchronized with a rising edge of the input pulse signal; and a second pulse generator generating the second pulse signal synchronized with a rising edge of the reference pulse signal. 
   The first pulse generator may include: a first inverter inverting a signal level of the input pulse signal; a first delay delaying the input pulse signal whose signal level is inverted by the first inverter by a predetermined amount of time; and a first AND gate performing an AND operation of the signal level of the input pulse signal and a signal level of the delayed input pulse signal by the first delay, and the second pulse generator may include: a second inverter inverting a signal level of the reference pulse signal; a second delay delaying the reference pulse signal inverted whose signal level is inverted by the second inverter by a predetermined amount of time; and a second AND gate performing an AND operation of the signal level of the reference pulse signal and a signal level of the delayed reference pulse signal by the second delay. 
   A duty cycle of the first pulse signal may be the same as that of the second pulse signal. 
   The detection unit may include: a first RS latch having a terminal S through which the first pulse signal is input, a terminal R through which a feedback signal is input, and a terminal Q through which a result of comparison between the first pulse signal and the feedback signal is output; a second RS latch having a terminal S through which the second pulse signal is input, a terminal R through which a feedback signal is input, and a terminal Q through which a result of comparison between the second pulse signal and the feedback signal is output; an AND gate performing an AND operation of the result of comparison between the first and second RS latches; and a delay delaying a result of the AND operation performed by the AND gate by a predetermined amount of time. 
   The phase detection apparatus may further include: a third inverter inverting a signal level of the comparison result of the first RS latch; and a fourth inverter inverting a signal level of the comparison result of the second RS latch. 
   The phase detection apparatus may further include a charging/discharging unit charging or discharging a predetermined current according to a comparison signal whose signal level is inverted by the third inverter and a comparison signal whose signal level is inverted by the fourth inverter, and outputting a phase detection signal corresponding to a phase difference between the first pulse signal and the second pulse signal. 
   The charging/discharging unit may include: a first current source having a predetermined current; a first switch opening or closing a current carrying path of the current of the first current source according to the comparison signal whose signal level is inverted by the third inverter; a capacitor charging or discharging the current of the first current source according to whether the first switch is turned on or off; a second switch opening or closing a path of the current discharged from the capacitor according to the comparison signal whose signal level is inverted by the fourth inverter; and a second current source having a predetermined current. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a configuration view illustrating a phase detection apparatus according to an exemplary embodiment of the invention; 
       FIG. 2  is a configuration view illustrating a pulse generator used in the phase detection apparatus according to the exemplary embodiment of the invention; and 
       FIGS. 3A to 3C  are timing charts illustrating signal waveforms of components of the phase detection apparatus with the timing between an input pulse signal and a reference pulse signal according to the exemplary embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
   The invention may however be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the shapes and dimensions may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like components. 
     FIG. 1  is a configuration view illustrating a phase detection apparatus according to an exemplary embodiment of the invention. 
   Referring to  FIG. 1 , a phase detection apparatus  100  includes a pulse generation unit  110  and a detection unit  120 . 
   The pulse generation unit  110  includes a first pulse generator  111  and a second pulse generator  112 . The first pulse generator  111  receives an input pulse signal A that has a variable duty cycle and a predetermined phase. The second pulse generator  112  receives a reference pulse signal B that has a predetermined phase and a predetermined duty cycle. 
   The first pulse generator  111  generates a first pulse signal on an edge of the input pulse signal A. The second pulse generator  112  generates a second pulse signal on an edge of the reference pulse signal B. 
     FIG. 2  is a configuration view illustrating a pulse generator used in the phase detection apparatus according to the embodiment to the invention. 
   Referring to  FIG. 2 , the first pulse generator  111  includes a first inverter  111   a , a first delay  111   b , and a first AND gate  111   c.    
   The first inverter  111   a  inverts a signal level of the input pulse signal A. Then, the first delay  111   b  delays the input pulse signal A whose signal level is inverted by the first inverter  111   a  by a predetermined amount of time. The first AND gate  111   c  performs an AND operation of the signal level of the input pulse signal A and a signal level of the delayed input pulse signal A by the first delay  111   b . Then, the first AND gate  111   c  outputs a first pulse signal A′ that is synchronized with a rising edge of the input pulse signal A. 
   An ON-period of the first pulse signal A′ is determined according to the delay time of the first delay  111   b.    
   Though not shown in  FIG. 2 , the second pulse generator  112  may include a second inverter, a second delay, and a second AND gate, each of which performs the same function as that of the first pulse generator  111 . The second pulse generator  112  may output a second pulse signal B′ that is synchronized with a rising edge of the reference pulse signal B. Further, by causing a delay time of the second delay to be equal to the delay time of the first delay  111   b , the first pulse signal A′ and the second pulse signal B′ can have the same duty cycle. 
   Referring to  FIG. 1 , the detection unit  120  includes a first RS latch  121 , a second RF latch  122 , a first inverter  123 , a second inverter  124 , an AND gate  125 , and a delay  126 . 
   The first RS latch  121  includes a terminal S through which the first pulse signal A′ is input, a terminal R through which a feedback signal is input, and a terminal Q through which a result of a logical operation of the signal level of the first pulse signal A′ and a signal level of the feedback signal is output. 
   In the same manner, the second RS latch  122  includes a terminal S through which the second pulse signal B′ is input, a terminal R through which the feedback signal is input, and a terminal Q through which a result of a logical operation of the signal level of the second pulse signal B′ and the signal level of the feedback signal is output. 
   The first inverter  123  inverts a signal level of an output signal from the first RS latch  121 . The second inverter  124  inverts a signal level of an output signal from the second RS latch  122 . 
   The AND gate  125  performs an AND operation of the output signals from the first and second RS latches  121  and  122 . The delay  126  delays a result of the AND operation performed by the AND gate  125  by a predetermined amount of time, and supplies the delayed result as the feedback signal. 
   Meanwhile, the phase detection apparatus  100  according to the embodiment of the invention may further include a charging/discharging unit  130 . 
   The charging/discharging unit  130  includes a first current source  131 , a first switch  132 , a second switch  133 , a second current source  134 , and a capacitor  135 . 
   The first current source  131  has a predetermined current. The first switch  132  opens or closes a current carrying path from the first current source  131  according to an output signal whose signal level is inverted by the first inverter  123 . The capacitor  135  charges or discharges the current from the first current source  131  according to the switching operation of the first switch  132 , and outputs a phase detection signal corresponding to a phase difference between the input pulse signal A and the reference pulse signal B. 
   The second switch  133  opens or closes a current discharging path of the current charged in the capacitor  135  according to an output signal whose signal level is inverted by the second inverter  124 . The second current source  134  has a current corresponding to the current from the capacitor  135 . 
     FIGS. 3A to 3C  are timing charts illustrating signal waveforms of components of the phase detection apparatus with the timing between an input pulse signal and a reference pulse signal according to an exemplary embodiment of the invention. 
   In  FIG. 3A , the input pulse signal A leads the reference pulse signal B. In  FIG. 3B , the input pulse signal A lags the reference pulse signal B. In  FIG. 3C , the input pulse signal A and the reference pulse signal B are phase locked to each other. 
   Referring to  FIGS. 1 ,  2 ,  3 A, and  3 B, when the input pulse signal A leads the reference pulse signal B, or when the input pulse signal A lags the reference pulse signal B, the phase detection apparatus according to the embodiment of the invention accurately detects a phase difference between the input pulse signal A and the reference pulse signal B. Referring to  FIG. 3C , even when the input pulse signal A and the reference pulse signal B have different duty cycles, if the input pulse signal A and the reference pulse signal B are accurately phase locked to each other, there is no phase difference. 
   As set forth above, according to the exemplary embodiment of the invention, even when an input signal and a reference signal have different duty cycles, a phase difference between the input signal and the reference signal can be accurately detected by using pulse signals on edges of the input signal and the reference signal. 
   While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.