Abstract:
An apparatus and method for detecting vertical blanking intervals (VBI) is disclosed. The apparatus can identify and filter non-VBI signals, and calculate a level value for digitization corresponding to the type of television signals. The apparatus includes a detecting unit and a coupled computing unit. The detecting unit is for generating a detecting signal according to a television signal. The computing unit is for calculating a slope of the detecting signal, and for determining whether the television signal contains a clock run-in signal according to the slope.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to the vertical blanking interval (VBI) of TV signals, and more particularly, to an apparatus and method for detecting the vertical blanking interval.  
         [0003]     2. Description of the Prior Art  
         [0004]     The vertical blanking interval (VBI) is a blank interval reserved in a TV signal for the attachment of all kinds of user information.  FIG. 1  shows the positions of scan lines for the VBI in different TV specifications. In the National Television System Committee (NTSC) system, each video frame has 525 scan lines; in the Phase Alternating Line (PAL) system, each video frame has 625 scan lines.  FIG. 1  illustrates the scan line numbers for Closed Caption (CC), Copy Generation Management System (CGMS), Wildscreen Signaling (WSS), Video Programming System (VPS), and Teletext (TTX) 625B.  
         [0005]      FIG. 2  is a schematic diagram of a typical VBI signal. As shown, the VBI signal contained in a scan line comprises the following portions: Hsync signal, color burst signal, clock run-in signal, frame code and data. Different VBI types correspond to different clock run-in signals and frame codes. A conventional VBI decoder is configured according to scan lines positions for a VBI signal within the TV signal. For example, VBI decoding is set to start when the scan line at a certain position is received. The VBI decoding first digitizes the received signals in reference to a preset constant level, for example, the DC voltage level, where the received signal is taken as 1 if its level is above the preset level, and 0 if its level is below the preset level. Next, the digitized signals are subject to slicing and parsing to complete the decoding.  
         [0006]     However, the prior art is unable to identify whether the received signal is a VBI signal and hence unable to filter non-VBI noises. In addition, different reference levels needs to be set for different TV specifications, and also the level value should vary under different operating conditions. Hence using a constant reference level for signal digitizing lacks flexibility and accuracy.  
       SUMMARY OF INVENTION  
       [0007]     It is therefore an object of the present invention to provide a VBI detection apparatus and method which can identify and automatically filter non-VBI noises.  
         [0008]     Another object of the present invention is to provide a VBI detection apparatus and method, which can compute a corresponding level value for digitizing different types of TV signals.  
         [0009]     A further object of the present invention is to provide a VBI decoder which includes the above VBI detection apparatus to enhance its performance.  
         [0010]     According to an embodiment of the present invention, an apparatus for detecting a vertical blanking interval is provided. The apparatus comprises: a first detecting unit which generates a detecting signal according to a TV signal; and a computing unit coupled to the first detecting unit to compute a slope of the detecting signal and determine whether the TV signal contains a clock run-in signal according to the computed slope.  
         [0011]     According to another embodiment of the present invention, a method for detecting a vertical blanking interval is provided. The method comprises the steps of: generating a detecting signal according to a TV signal; computing a slope of the detecting signal; and determining whether the TV signal contains a clock run-in signal according to the slope. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The details of the present invention will be more readily understood from a detailed description of the preferred embodiments taken in conjunction with the following figures.  
         [0013]      FIG. 1  shows the scan line positions for different VBI types.  
         [0014]      FIG. 2  is a schematic diagram of a typical VBI signal.  
         [0015]      FIG. 3  is a block diagram of a VBI detection apparatus according to a preferred embodiment of the invention.  
         [0016]      FIG. 4  is a diagram showing the correspondence between the clock run-in signal and the detecting signal in the embodiment of  FIG. 3 .  
         [0017]      FIG. 5A  is a block diagram of an embodiment of the first detecting unit in  FIG. 3 .  
         [0018]      FIG. 5B  and  FIG. 5C  are circuit diagrams respectively showing an embodiment of the IIR filter and the FIR filter in  FIG. 5A .  
         [0019]      FIG. 6  is a schematic diagram of another embodiment of the first detecting unit in  FIG. 3 .  
         [0020]      FIG. 7  is a flow chart of a VBI detection method according to a preferred embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]      FIG. 3  shows a block diagram of a VBI detection apparatus  30  according to an embodiment of the invention. The VBI detection apparatus  30  can detect different types of VBI signals in TV signals, such as CC, CGMS, WSS, VPS, TTX625B, etc. As shown, the VBI detection apparatus  30  comprises a first detecting unit  31 , a computing unit  32 , a digitizing circuit  33 , and a second detecting unit  34 . The first detecting unit  31  receives a TV signal and generates a detecting signal according to the TV signal. The TV signal is a CVBS signal, Y/C signal, VGA signal, or Y/Pb/Pr signal. The computing unit  32  coupled to the first detecting unit  31  is for computing a slope of the detecting signal, and then comparing the slope with a first threshold to determine whether the TV signal contains a clock run-in signal of the VBI signal.  
         [0022]      FIG. 4  is a diagram showing the correspondence between the clock run-in signal and the detecting signal in  FIG. 3 . When the first detecting unit  31  receives the clock run-in signal, it generates the corresponding detecting signal as shown in  FIG. 4 . The waveform of the detecting signal increases incrementally towards a stable value. The computing unit  32  would pick the values of the detecting signal via a window and compute its slope. The width of the window can be adjusted according to actual situations. When the difference of the right side value s_y and the left side value s_x of window-A is greater than the first threshold, it means the clock run-in signal is detected; when the difference is not greater than the first threshold, it means the TV signal does not contain a clock run-in signal, i.e. the TV signal is not a VBI signal but a filterable noise.  
         [0023]     After the clock run-in signal is detected, the computing unit  32  will compare the slope of the detecting signal with a second threshold to determine whether the first detecting unit  31  has locked a level value (or called DC level). The second threshold and the first threshold described above can be adjusted according to actual situations. When the difference of the right side value e_y and the left side value e_x of window-B is smaller than the second threshold, it means the first detecting unit  31  has locked the level value, which is the stable value approached by the detecting signal in  FIG. 4 . After the first detecting unit  31  has locked the level value, the computing unit  32  would emit a control signal to the digitizing circuit  33 . In one embodiment, the first detecting unit  31  includes an infinite impulse response (IIR) filter  311  and a finite impulse response (FIR) filter  312  serially connected as shown in  FIG. 5A .  FIG. 5B  and  FIG. 5C  are circuit diagrams showing an embodiment of the IIR filter  311  and the FIR filter  312 . As shown, the IIR filter  311  and FIR filter  312  are composed of arithmetic circuits and delay elements to generate the detecting signal. In another embodiment, the IIR filter  311  is serially connected behind the FIR filter  312 . In still another embodiment, as shown in  FIG. 6 , the first detecting unit  31  includes an integrator  313 , where the detecting signal is generated by adjusting the resistance R and capacitance C of the integrator  313 .  
         [0024]     After the high-frequency noise in the TV signal is filtered by a noise filter  35 , the TV signal is transmitted to the digitizing circuit  33 . After receiving the control signal emitted by the computing unit  32 , the digitizing circuit  33  converts the TV signal into a digital signal in reference to the level value provided by the first detecting unit  31 , where the TV signal is taken as 1 if the signal level is above the level value, and taken as 0 if the signal level is below the level value. The second detecting unit  34  is coupled to the digitizing circuit  33  to detect whether the digital signal contains a frame code. The second detecting unit  34  would decode the frame code, and compare it with the frame codes of various VBI types to determine whether the TV signal contains a VBI signal and to identify the type of the VBI signal. If the TV signal contains the VBI signal, the VBI signal is transmitted to a data slicer for subsequent processing.  
         [0025]     The VBI detection apparatus  30  in  FIG. 3  can be applied to a VBI decoder to identify and filter non-VBI noises, and according to the type of a detected VBI signal, lock a corresponding level value as a reference for digitizing the TV signal, thereby enhancing the operational flexibility and accuracy of the VBI decoder.  
         [0026]      FIG. 7  is a flow chart of a VBI detection method according to a preferred embodiment of the invention. The flow comprises the following steps:  
         [0027]     Step  70 : generate a detecting signal according to a TV signal;  
         [0028]     Step  71 : compute a slope of the detecting signal;  
         [0029]     Step  72 : determine whether the slope in a first interval is greater than a first threshold; if yes, execute step  73 , otherwise return to step  70 ;  
         [0030]     Step  73 : determine whether the slope in a second interval is less than a second threshold; if yes, execute step  74 , otherwise return to step  70 ;  
         [0031]     Step  74 : generate a level value according to the detecting signal;  
         [0032]     Step  75 : filter the noise of the TV signal;  
         [0033]     Step  76 : convert the TV signal into a digital signal in reference to the level value;  
         [0034]     Step  77 : detect whether the digital signal contains a frame code; if yes, execute step  78 , otherwise return to step  70 ; and  
         [0035]     Step  78 : determine whether the TV signal contains a VBI signal and the type of the VBI signal according to the detected frame code.  
         [0036]     In step  72 , it can be determined whether the TV signal contains a clock run-in signal. In step  74 , the level value produced is the stable value approached by the detecting signal. In steps  72 ,  73  and  77  if the outcome is negative, it means the TV signal does not contain a VBI signal, and the flow would return to step  70  to begin the detection for a next incoming TV signal.  
         [0037]     While the present invention has been shown and described with reference to the preferred embodiments thereof and in terms of the illustrative drawings, it should not be considered as limited thereby. Various possible modifications and alterations could be conceived of by one skilled in the art to the form and the content of any particular embodiment, without departing from the scope and the spirit of the present invention.