Patent Abstract:
A video signal output device comprises a signal processing unit which converts video and audio signals input via two signal paths to a time-division multiplex serial signal and outputs it, a changeover switch which has a plurality of output terminals and outputs the serial signal input from the signal processing unit through one of the output terminals which is selected according to a control signal, a plurality of digital interface terminals each of which is connected to a respective one of the output terminals of the changeover switch, and a control unit responsive to a command input from a user interface to supply the changeover switch with the control signal to select one of the output terminals to which the serial signal is output.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-194568, filed Jun. 30, 2004, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a video signal output device which outputs video and audio signals through digital interface terminals.  
         [0004]     2. Description of the Related Art  
         [0005]     Conventional video output devices, such as video tape recorders, output video and audio signals in analog form.  
         [0006]     In recent years, set-top boxes, such as DVD players and digital satellite broadcasting tuners, have been developed which output signals in digital form through digital interfaces, such as HDMI. Also, equipment which permits multimedia communications concurrently has been developed (see Japanese Unexamined Patent Publication No. 9-224081).  
         [0007]     Digital video output devices are equipped with only one digital interface (such as HDMI) output system and hence have only one output terminal for the digital interface.  
         [0008]     A problem is encountered in trying to use a digital video signal from the digital video output device with two or more domestic digital devices. That is, in reproducing an output video signal from the digital video output device on a television receiver or recording it on a DVD recorder, it is required to replace a cable for the interface with the digital. video output device with another.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     According to the present invention, there is provided a video signal output device comprising: a signal processing unit which converts video and audio signals input via two signal paths to a time-division serial signal and outputs it; an output selection unit which has a plurality of output terminals and outputs the serial signal input from the signal processing unit through one of the output terminals which is selected according to a control signal; a plurality of digital interface terminals each of which is connected to a respective one of the output terminals of the output selection unit; and a control unit responsive to a command input from a user interface to supply the output selection unit with the control signal to select one of the output terminals to which the serial signal is output.  
         [0010]     The video signal output device can supply various domestic digital devices with digital video signals without replacing an interfacing cable with another.  
         [0011]     Additional advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0012]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0013]      FIG. 1  is a block diagram of a video signal output device to which the principles of the present invention are applied;  
         [0014]      FIG. 2  shows the manner in which video data and audio data are transferred through HDMI;  
         [0015]      FIG. 3  is a block diagram of the output controller shown in  FIG. 1 ; and  
         [0016]      FIG. 4  is a flowchart illustrating the operation of the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     An embodiment of the present invention will be described hereinafter with reference to the accompanying drawings.  
         [0018]      FIG. 1  is a block diagram of a video signal output device to which the principles of the present invention are applied. The video signal output device  1  is a set-top box (STB) (e.g., a digital satellite broadcast receiver).  
         [0019]     The video signal output device, indicated generally at  1 , is equipped with a network adapter  6 , a digital broadcast signal input terminal  7 , a memory  8 , a decoder  9 , a tuner  10 , an output control unit  11 , a CPU  12 , a graphics processing unit  13 , HDMI output terminal  104   a,    104   b  and  104   c,  an analog signal output terminal  104   d,  a video and audio signal processing unit  16 , and an operating unit  17 .  
         [0020]     The input terminal  7  is connected to receive broadcast signals received by an antenna. The tuner  10  extracts a transport stream (TS) of specific program information from digital broadcast signals from the input terminal  7 . The decoder  9  decodes the extracted TS to output two signals: that is, a video signal and an audio signal, each of which is made up of a plurality of bits. The tuner  10  and the decoder  9  form signal producing means for producing decoded video and audio signals.  
         [0021]     The video and audio signal processing unit  16  converts the program video signal decoded by the decoder  9  to a signal compatible to video equipment to which the video signal is output, such as a television receiver  105 . The video and audio signal processing unit  16  converts each of the decoded program video and audio signals to an analog signal and then applies it to the analog signal output terminal  104   d.  An analog video signal and an analog audio signal are applied all the time to the analog signal output terminal  104   d  so long as the tuner  10  receives program information. The output control unit  11  converts two input signals, i.e., a video signal and an audio signal, to a time-division serial signal, i.e., an HDMI signal, and then transmits the resulting signal through one of the output terminals  104   a,    104   b,  and  104   c.  In the HDMI, digital video data and digital audio data are transferred serially on a time division multiplex basis as shown in  FIG. 2 .  
         [0022]     The operating unit  17  is a user interface equipped with various keys which accept a variety of input operations, for example, a remote controller. The CPU  12  responds to input signals from the operating unit  17  to control the components in the video signal output device  1 . The memory  8  includes a ROM storing a program according to the present invention and a RAM used as a working area for the CPU  12 . The graphics processing unit  13  produces on-screen display (OSD) images when necessary. The network adapter  6  provides the interface to a communications network.  
         [0023]     The output control unit  11  will be described next with reference to  FIG. 3 .  
         [0024]     The output control unit  11  has an HDMI signal output unit  101 , a changeover switch  103 , and HDMI output terminals  104   a,    104   b,  and  104   c.  The HDMI signal output unit  101  converts video and audio signals transferred over two signal paths from the video and audio processing unit  16  to a serial signal of video data and audio data as shown in  FIG. 2 . The HDMI signal output unit  101  is comprised of an integrated circuit such as an LSI. The video and audio processing unit  16  and the HDMI signal output unit  101  may be fabricated as one LSI.  
         [0025]     A microcomputer  102  changes over the switch  103  when commanded by the CPU  12 . Thereby, the serial video/audio signal output from the HDMI signal output unit  101  is output from one of the HDMI output terminals  104   a,    104   b,  and  104   c.  The HDMI output terminals  104   a,    104   b  and  104   c  are connected to video devices  105 ,  106  and  107  by HDMI dedicated cables  108   a,    108   b  and  108   c,  respectively.  
         [0026]     Signal lines which connect the HDMI signal output unit  101 , the changeover switch  103 , and the output terminals  104   a  to  104   c  include signal lines to transmit an extended display identification data (EDID) signal and so on in addition to a signal line to transmit the serial video/audio signal. The EDID is data used for the display side (e.g., the television receiver  105 ) to cause the host side (the video signal output device  1 ) to recognize information on the display side (resolution, the number of pixels, etc.). The video devices  105 ,  106  and  107  have EDID memories  109   a,    109   b  and  109   c,  respectively. Each of the video devices stores its own EDID in its EDID memory. The micro-computer  102  reads in the EDID of the video devices  104   a,    104   b  and  104   c  connected to the output terminals  104   a,    104   b  and  104   c  via the changeover switch  103  and holds the EDID. The video and audio processing unit  16  processes video data on the basis of user-specified video device EDID. Thus, video data output from the HDMI signal output unit  101  is made compatible with the video device to which it is output.  
         [0027]      FIG. 4  is a flowchart illustrating the operation of the embodiment described above.  
         [0028]     The CPU  12  makes a decision of whether a signal to identify one of the HDMI output terminals  104   a,    104   b  and  104   c  has been input from the user via the operating unit  17  (step ST 01 ). If such a signal has been input (YES in step ST 01 ) and it indicates the output terminal  104 b (YES in step ST 02 ), the CPU  12  commands the microcomputer  102  to set the changeover switch  105  to the output terminal  104   b  position. The CPU then sets processing in the video and audio processing unit  16  to conform to the EDID of the video device  106  connected to the output terminal  104   b.  Thereby, the video and audio processing unit  16  is allowed to produce the optimum video signal for the television receiver  106 .  
         [0029]     If the signal indicates the output terminal  104   c  (YES in step ST 05 ) but not the output terminal  104   b  (NO in step ST 02 ), the CPU  12  commands the microcomputer  102  to set the changeover switch  103  to the output terminal  104   c  position (step ST 06 ). The CPU then sets the processing in the video and audio processing unit  16  on the basis of the EDID of the video device  107  connected to the output terminal  104   c  (step ST 07 ).  
         [0030]     If the signal does not indicate the output terminal  104   c  (NO in step ST 05 ) or no signal to identify one of the output terminals  104   a  to  104   c  is input (NO in step ST 01 ), the CPU  12  commands the microcomputer  102  to set the changeover switch  103  to the output terminal  104   a  position (step ST 08 ). The CPU then sets processing in the video and audio processing unit  16  to conform to the EDID of the video device  105  connected to the output terminal  104   a  (step ST 09 ). Thereby, the video and audio processing unit  16  is allowed to produce the optimum video signal for the television receiver  105 . For example, even if the television receivers  105  and  106  differ in resolution or aspect ratio, each of them is allowed to receive the optimum video signal.  
         [0031]     Thus, according to this embodiment, signals output from the HDMI signal output unit  101  are output externally from two or more HDMI output terminals via the changeover switch  103 . Accordingly, video signals can be applied to various digital video devices without replacing an interfacing cable with another. In addition, video and audio signals can be applied to two or more video devices using one HDMI signal processing LSI; thus, an increase in the cost of the video output device can be prevented in comparison with the case where two or more HDMI signal processing LSIs are used.  
         [0032]     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Technology Classification (CPC): 7