Patent Publication Number: US-2010129060-A1

Title: Digital broadcast receiving apparatus and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2008-117623, filed on Nov. 25, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Apparatuses and methods consistent with the present invention relate to digital broadcast receiving apparatus and method, and more particularly, to a digital broadcast receiving apparatus in which a user is able to watch a program while recording a different program using a single oscillator and a digital broadcast receiving method thereof. 
     2. Description of the Related Art 
     Recently, a digital broadcast receiving apparatus provides a function of reproducing an incoming transport stream to be watchable and simultaneously recording a different transport stream to a recording medium. In order to perform this function, the digital broadcast receiving apparatus accurately extracts a time stamp when recording and reproducing the transport streams and combines the time stamp with the transport streams, or extracts a time stamp from the transport streams. However, the function of reproducing a program and simultaneously recording a different program requires two clock sources (oscillators) since the two programs have different program clock references (PCR). 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an exemplary embodiment of the present invention may not overcome any of the problems described above. 
     The an exemplary embodiment of the present invention provides a digital broadcasting apparatus which uses a single oscillator when reproducing and recording two or more different programs simultaneously, thereby providing a cost saving effect, and also minimizes a PCR jitter which may occur due to the use of a single oscillator, and a digital broadcasting method thereof. 
     Consistent with an aspect of the present invention, a digital broadcasting apparatus comprises an oscillator which changes a reference frequency of a system clock of the digital broadcasting apparatus using a PCR W , which is a program clock reference (PCR) of a first transport stream, a record clock counter which tunes a record arriving time clock (ATC) which is generated from the changed reference frequency and generates a tuned record ATC which is necessary to record a second transport stream different from the first transport stream, and a record stream interface which adds a time stamp to the second transport stream using the tuned record ATC and outputs the second transport stream with the time stamp to a recording device. 
     The digital broadcasting apparatus may further comprise a controller which calculates a ratio which is necessary to generate the tuned record ATC using the generated record ATC and a PCR R  which is a PCR of the second transport stream. 
     The controller may latch the record ATC corresponding to the point of time that the PCR R  is input at least two times, and may calculate a ratio of a difference between the at least two latched record ATCs and a difference between the at least two PCR R s as a ratio necessary to generate the tuned record ATC. 
     The record clock counter may generate the tuned record ATC using the following equation: 
       Tuned ATC( k )=ATC( k )×(PCR n −PCR n-1 )/(ATC n −ATC n-1 ) 
     wherein the Tuned ATC(k) denotes a tuned record ATC, ATC(k) denotes the kth record ATC, PCR n  denotes the nth PCR, ATC n  denotes a ATC corresponding to the point of time that the PCR n  is input, and k and n are constants. 
     The record stream interface may add the tuned record ATC corresponding to the point of time that the second transport stream is input as the time stamp. 
     The digital broadcasting apparatus may further comprise a system clock recovery device which generates a PWM signal which corresponds to a difference between a counting value of a system time counter (STC) generated from the system clock and the PCR W , and recovers the system clock, and the oscillator may change the reference frequency of the system clock using the PWM signal. 
     The digital broadcasting apparatus may further comprise a de-multiplexer which selects one of the first transport stream which is being replayed and the second transport stream which is recorded to the recording device, and a decoder which decodes the selected one transport stream. 
     Consistent with another aspect of the present invention, a digital broadcasting method of a digital broadcasting apparatus, comprises changing a reference frequency of a system clock using a PCR W  which is a PCR of a first transport stream, tuning a record ATC which is generated from the changed reference frequency and generating a tuned record ATC which is necessary to record a second transport stream different from the first transport stream, and adding a time stamp to the second transport stream using the tuned record ATC and recording the second transport stream with the time stamp to a recording device. 
     The digital broadcasting method may further comprise calculating a ratio which is necessary to generate the tuned record ATC using the generated record ATC and a PCR R  which is a PCR of the second transport stream. 
     The calculating operation may comprise latching the record ATC corresponding to the point of time that the PCR R  is input at least two times, and calculating a ratio of a difference between the at least two latched record ATCs and a difference between the at least two PCR R s as a ratio necessary to generate the tuned record ATC. 
     The operation of generating the tuned record ATC may use the following equation: 
       Tuned ATC( k )=ATC( k )×(PCR n −PCR n-1 )/(ATC n −ATC n-1 ) 
     wherein the Tuned ATC(k) denotes a tuned record ATC, ATC(k) denotes the kth record ATC, PCR n  denotes the nth PCR, ATC n  denotes a ATC corresponding to the point of time that the PCR n  is input, and k and n are constants. 
     The recording operation may add the tuned record ATC corresponding to the point of time that the second transport stream is input as the time stamp. 
     The digital broadcasting method may further comprise generating a PWM signal which corresponds to a difference between a counting value of a STC generated from the system clock and the PCR W , and recovering the system clock, and the changing operation may change the reference frequency of the system clock using the PWM signal. 
     Consistent with still another aspect of the present invention, a digital broadcasting apparatus which records a second transport stream which is different from a first transport stream which is being replayed, comprises oscillator which changes a reference frequency of a system clock, a recording device which records the second transport stream, and a controller which, if a ratio of a difference between time stamps of the second transport stream recorded to the recording device and a difference between PCRs of the second transport stream is less than a reference value, determines that replaying and recording operations are simultaneously performed using the single oscillator. 
     Additional and/or other aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The above and/or other aspects of exemplary embodiments of the present invention will be more apparent by describing certain exemplary embodiments of the present invention with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a digital broadcast receiving apparatus consistent with an exemplary embodiment of the present invention; 
         FIG. 2  is a view illustrating a process of generating a tuned record arriving time clock (ATC); 
         FIG. 3  is a flowchart illustrating a digital broadcast receiving method of a digital broadcast receiving apparatus consistent with an exemplary embodiment of the present invention; 
         FIG. 4  is a flowchart illustrating a method for recording a second transport stream (TS) to a recording device after operation  5360  of  FIG. 3 ; and 
         FIG. 5  is a block diagram a digital broadcast receiving apparatus consistent with another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Certain exemplary embodiments of the present invention will now be described in greater detail with reference to the accompanying drawings. 
     In the following description, same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the invention. Thus, it is apparent that the exemplary embodiments of the present invention can be carried out without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the invention with unnecessary detail. 
       FIG. 1  is a block diagram illustrating a digital broadcast receiving apparatus consistent with an exemplary embodiment of the present invention. A digital broadcast receiving apparatus  100  shown in  FIG. 1  may have a personal video recorder (PVR) function. The digital broadcast receiving apparatus  100  receives transport streams (TSs) conforming to the standard of moving picture experts group-2 (MPEG-2) and combines a time stamp which is information necessary for synchronization with each of the TSs when recording the received TSs to a recording device  190 . The TS which has been recorded is synchronized and reproduced based on the time stamp. 
     Also, the digital broadcast receiving apparatus  100  reproduces a first program to be watched by a user and simultaneously records a second program to the recording device  190  using a single oscillator, that is, a single clock source. 
     The digital broadcast receiving apparatus  100  comprises a first receiver  105  and a second receiver  110 , a first TS de-multiplexer  120 , an oscillator  130 , an audio/video (AV) decoder  140 , a second TS de-multiplexer  150 , a controller  160 , a record stream buffer  170 , and a replay stream buffer  180 . Other components which are required to realize the present invention, such as a memory, a control program, and software, are omitted for convenience of explanation. 
     The recording device  190  may be provided in the digital broadcast receiving apparatus  100  if the digital broadcast receiving apparatus  100  is a PVR, or may be connected to the digital broadcast receiving apparatus  100  through a cable or a terminal. 
     The first receiver  105  receives a first program to be watched and the second receiver  110  receives a second program to be recorded. The first and the second receivers  105 ,  110  may be tuners or cable terminals which are connected to an external device. The first and the second receivers  105 ,  110  may receive multi-programs, respectively. That is, each of the first and the second receivers  105 ,  110  may receive two or more different programs, in which case a first packet ID (PID) filter  122  and a second PID filter  151  are capable of filtering desired first and second programs. 
     The first and the second programs consist of digital broadcast TSs which are MPEG-2 TSs, for example. The first and the second programs may be received through a single receiver but in this embodiment the first and the second programs are received through the two receivers  105 ,  110 , respectively. 
     The first TS de-multiplexer  120  serves as a replay de-multiplexer for processing the received first program into signals which are capable of being watched or reproducing a program recorded in the recording device  190 , and comprises a switch  121 , the first PID filter  122 , a TS parser  123 , and a system clock recovery unit  124 . 
     The switch  121  selects one of the first program received through the first receiver  105  and the second program stored in the recording device  190 . The selected program may be selected by a user. Hereinafter, the case where the first program is selected will be described. 
     The first PID filter  122  filters the first program to extract a first TS which includes a PCR W , which is a PCR (program clock reference, it also means reference clock counter or program clock counter) of the first program, and an AV signal. The first TS indicates a TS of the first program and the second TS indicates a TS of the second program. 
     The TS parser  123  parses the first TS to generate an AV elementary stream (ES) which is capable of being decoded. 
     The system clock recovery unit  124  comprises a system time counter (STC)  124   a  to count a system clock input from the oscillator  130 , and performs a system clock recovery process using a difference between a counting result of the STC  124   a  and the PCR W . 
     The system clock recovery means outputting a control signal corresponding to the difference so that the difference between the counting result and the PCR W  is equal to ‘0’. The control signal may be a PWM signal for example and may be input to the oscillator  130 . The system clock recovery is performed every time that the PCR W  is filtered by and input from the first PID filter  122 . 
     The oscillator  130  generates a reference clock, that is, a system clock corresponding to a reference frequency of the digital broadcast receiving apparatus  100 , and transmits the system clock to the system clock recovery device  124 . The reference frequency may be 27 MHz±αHz. Also, the oscillator  130  may change the reference frequency using the PCR W  which is included in the first TS of the first program. 
     That is, the oscillator  130  may change the reference frequency to synchronize the reference frequency with the first program using the PWM signal input from the system clock recovery device  124 . The changed reference frequency is input to the system clock recovery device  124 , the AV decoder  140 , a record clock counter  152 , or a replay clock counter  154 . 
     The A/V decoder  140  decodes the ES of the first program which is input from the TS parser  123  to output watchable signals. The A/V decoder  140  adjusts a horizontal synchronization signal and a vertical synchronization signal of the ES using a clock ({circle around (a)}) of the reference frequency which is being changed by the oscillator  130 . 
     The second TS de-multiplexer  150  serves as a record de-multiplexer for processing the second program into signals which are capable of being recorded, and comprises the second PID filter  151 , the record clock counter  152 , a record stream interface unit  153 , the replay clock counter  154 , and a replay stream interface unit  155 . 
     The second PID filter  151  filters the second program input from the second receiver  110  to extract a second TS which includes a PCR R , which is a PCR of the second program, and the AV signal. 
     The record clock counter  152  tunes a record arriving time clock (ATC) generated from the reference frequency changed by the oscillator  130  to generate a tuned record ATC which is necessary to record the second TS. A result of tuning the record ATC is the tuned record ATC which is necessary to record the second TS. 
     More specifically, if a system clock corresponding to the changed reference frequency is input as shown in  FIG. 2 , the record clock counter  152  generates a record ATC corresponding to the input system clock and counts the generated record ATC. The system clock corresponding to the changed reference frequency is a clock which is synchronized with the first program (that is, a watchable program). 
     The controller  160  calculates a ratio which is necessary to tune the record ATC generated by the record clock counter  152  and the PCR R  input from the second PID filter  151 . Based on the calculated ratio, the controller  160  tunes an error of a record clock counter generated from the reference clock of the first program with respect to the reference clock of the second program, thereby generating the tuned record ATC as a result. 
     More specifically, the controller  160  latches the record ATC corresponding to the point of time that the PCR R  is input from the second PID filter  151  at least two times. The controller  160  calculates a difference between the at least two latched record ATCs and a difference between the at least two PCR R s corresponding to the two latched record ATCs, and outputs a ratio of the two differences as a ratio for tuning the record ATC. Since the difference between the two PCR R s, that is, the PCR interval, indicates a difference between the reference clocks of the second TS to be stored, or a difference between the reference clocks of the broadcasting station providing the second TS, the difference is used to calculate a tuned record ATC. 
     The controller  160  latches the record ATC corresponding to the PCR R , records the latched record ATC to a memory (not shown) every time that the PCR R  is input from the second PID filter  151 , and a previous PCR R  and a current PCR R . This is because the current PCR R  and the previous PCR R  and their corresponding record ATCs are used to calculate the ratio. 
     Referring to  FIG. 2 , the controller  160  latches a counting value ATC 1  of the record ATC corresponding to the point of time that the PCR R1  is input from the second PID filter  151 , and latches a counting value ATC 2  of the record ATC corresponding to the point of time that the PCR R2 , which is the next PCR R  of the PCR R1 , is input. The controller  160  subtracts the ATC 1  from the ATC 2 , subtracts the PCR R1  from the PCR R2 , and then calculates a ratio of two subtracting results. Herein, PCR R1 , PCR R2 , ATC 1 , ATC 2  may be expressed by counting values and may be recorded to the memory. 
     The record clock counter  152  multiplies the ratio for tuning which is calculated by the controller  160  with the record ATC to generate a tuned record ATC. That is, the tuned record ATC is a result of correcting the record ATC to be suitable for recording the second TS. 
     The record clock counter  152  generates a tuned record ATC using the record ATC based on the following equation: 
       Tuned ATC( k )=ATC( k )×(PCR Rn −PCR Rn-1 )/(ATC n −ATC n-1 )  [Equation 1] 
     wherein tuned ATC(k) denotes a tuned record ATC, which is a result of tuning the kth record ATC, ATC(k) denotes the kth record ATC, k denotes a counting value of the record ATC, PCR Rn  denotes the nth PCR, and ATC n  denotes an ATC corresponding to the point of time that PCR Rn  is input. 
     Also, (PCR Rn −PCR Rn-1 )/(ATC n −ATC n-1 ) denotes a ratio which is necessary to tune the record ATC. The calculated ratio is same during the PCR interval and the ATC(k) progressively increases for each clock. 
     For example, if the calculated ratio is less than ‘1’, that is, if (PCR Rn −PCR Rn-1 ) is less than (ATC n −ATC n-1 ), the record clock counter  152  generates a tuned record ATC in which two or more clocks are counted as one clock as shown in  FIG. 2 . To the contrary, if the calculated ratio is greater than ‘1’, the record clock counter  152  generates a tuned record ATC in which one clock is counted two or more times. 
     Referring back to  FIG. 1 , the record stream interface unit  153  continuously receives the tuned record ATC (e.g., the tuned ATC of  FIG. 2 ) from the record clock counter  152 . The record stream interface  153  latches the tuned record ATC corresponding to the point of time that the second TS is input from the second PID filter  151 , and adds the latched ATC to the second TS as an arriving time stamp (ATS), thereby generating a source packet. The ATS may be added to the payload of a TS as a header and may include flags. 
     The record stream interface  153  temporarily stores the second TS with the ATS to the record stream buffer  170 , and then records the second TS to the recording device  190  through a data bus  195 . 
     If a replay of the second TS recorded to the recording device  190  is requested, the controller  160  temporarily stores the second TS recorded to the recording device  190  to the replay stream buffer  180 , and transmits the second TS which is temporarily stored to the replay stream interface  155  through the data bus  195 . 
     The replay clock counter  154  receives the system clock from the oscillator  130  and generates the ATC through the free run. The free run refers to a process of continuously counting the record ATC from an initial value (for example, ‘0’). 
     The replay stream interface  155  outputs the second TS to the switch  121  if a replay ATC input from the replay clock counter  154  is identical to the time stamp of the second TS, that is, the ATS, which is input from the replay stream buffer  180 . The switch  121  switches to the second TS and transmits the second TS to the first PID filter  122 . 
     After that, the system clock recovery device  124  generates a control signal such as a PWM signal based on the PCR R  of the second TS and the reference frequency, and the oscillator  130  synchronizes the reference frequency with the second TS using the control signal. The synchronized reference frequency, that is, the changed reference frequency is input to the replay clock counter  154  such that the above operation is repeated. 
     As described above, the oscillator  130  for replaying a program can be used to adjust the reference frequency and generate the time stamp necessary to record the second TS. To this end, an oscillator for recording a program is not additionally required so that an additional cost cannot be incurred, and also, since it is possible to generate a tuned record ATC, a jitter can be prevented. 
       FIG. 3  is a flowchart illustrating a digital broadcast receiving method of the digital broadcast receiving apparatus consistent with an exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 to 3 , when the first TS of the first program is replayed as watchable signals (S 305 ), if a record of the second program is requested (S 310 ), the record clock counter  152  initializes a record ATC and performs the free run (S 315 ). 
     The second PID filter  151  filters the second program received through the second receiver  110  and extracts the second TS (S 320 ). 
     The record clock counter  152  receives a reference frequency which is changed by the oscillator  130 , and generates a record ATC and transmits the record ATC to the controller  160  (S 325 ). 
     If the PCR Rn-1  is extracted by the second PID filter  151  (S 330 ), the controller  160  latches the record ATC n-1  corresponding to the PCR Rn-1  at the record ATC input in operation S 320  (S 335 ). 
     If the PCR Rn , which is the next PCR R , is extracted by the second PID filter  151  (S 340 ), the controller  160  latches the record ATC n  corresponding to the PCR Rn  at the record ATC input in operation S 320  (S 345 ). 
     The controller  160  calculates a ratio which is necessary to tune the ATC(k) using the PCR Rn-1 , PCR Rn , ATC n-1 , ATC n  which are obtained in operations S 330  to S 345  (S 350 ), wherein the ATC(k) denotes a counting value of the kth record ATC. 
     The record clock counter  152  multiplies the ratio calculated in operation S 350  with the ATC(k), calculates a tuned record ATC, and transmits the tuned record ATC to the record stream interface  153  (S 355 ). 
     If the next PCR R  is extracted by updating to n=n+1, the controller  160  repeats operations S 335  to S 355  (S 360 ). 
       FIG. 4  is a flowchart illustrating a method for recording the second TS to the recording device after operation S 360 . 
     If the second TS is input to the record stream interface  153  (S 405 ), the record stream interface  153  latches the tuned record ATC which corresponds to the point of time that the second TS is input (S 410 ). 
     The record stream interface  153  generates a source packet shown in  FIG. 2  using the tuned record ATC which has been latched in operation S 410  and the second TS (S 415 ). 
     The controller  160  controls the record stream interface  153  to temporarily store the source packet to the record stream buffer  170  and then record it to the recording device  190  (S 420 ). 
       FIG. 5  is a block diagram illustrating a digital broadcast receiving apparatus consistent with another exemplary embodiment of the present invention. 
     Although a digital broadcast receiving apparatus  500  of  FIG. 5  may perform the same function as the digital broadcast receiving apparatus  100  of  FIG. 1 , detailed illustration and description are omitted for the sake of simplicity. The digital broadcast receiving apparatus  500  is capable of replaying a first TS corresponding to a first channel and simultaneously recording a second TS corresponding to a second channel using a single oscillator  510 . 
     The oscillator  510  shown in  FIG. 5  changes a reference frequency set in the digital broadcast receiving apparatus  500  by synchronizing the reference frequency with the first TS. To this end, the system clock corresponding to the reference frequency is utilized in replaying the first TS or recording the second TS. 
     A recording device  520  records the second TS which is requested to be recorded. The recording device  520  may be provided in the digital broadcast receiving apparatus  500  or may be an external recording medium which is removably mounted on the digital broadcast receiving apparatus  500 . The second TS is allocated a time stamp in the method described above with reference to  FIGS. 1 to 3 . 
     If a ratio of a difference between the time stamps of the second TS recorded to the recording device  520  and a difference between the PCRs of the second TS is less than a reference value, the controller  530  determines that the digital broadcast receiving apparatus  500  simultaneously replays and records different programs using the single oscillator  510 . The reference value is stored to a memory (not shown) and may be ‘1’. That is, the controller determines whether to use the single oscillator  510  by determining whether the value 
     
       
         
           
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     is less than 1. 
     The foregoing exemplary embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.