Patent Publication Number: US-2009237561-A1

Title: Video and audio output device

Description:
TECHNICAL FIELD 
     The present invention relates to video and audio output devices for transmitting video data and audio data. More particularly, the present invention relates to a video and audio output device which transmits video and audio data in the High Definition Multimedia Interface (HDMI) standard. 
     BACKGROUND ART 
     Conventionally, the Digital Visual Interface (DVI) standard has been well known as a standard for transmitting video data as digital data. With this standard, pixel data in the primary color signals RGB is converted to digital data per pixel, and the video is digitally transmitted using an uncompressed baseband. 
     Meanwhile, in recent years, the HDMI standard has been established, in which a video and audio output device such as a DVD recorder and a video and audio reproduction device such as a TV are connected with a cable, and digital data outputted from the video and audio output device is transmitted to the video and audio reproduction device. With this technology, audio data is multiplexed, compressed, and superimposed in a blanking period of the video signals and simultaneously transmitted with video signals. This is highly convenient for a user since it is not necessary to connect an audio output terminal to a TV and the like aside from a video output terminal as in the conventional technology, and it is expected that the technology will be more widely used. 
     The data transmission using the HDMI based on the HDMI standard in non-patent reference 1 will be described with reference to the drawings. First,  FIG. 5  shows a block diagram of a conventional video and audio output device. 
     Digital video data and audio data are transmitted from a transmitter  407  on the transmission side to a receiver  408  on the reception side. A video and audio output device  410  which is a video and audio signal source such as a DVD recorder includes the transmitter  407 , and a video and audio reproduction device  412  includes the receiver  408 . The transmitter  407  encodes video signals and audio signals and outputs the signals to the receiver  408 . The transmitter  407  converts, by encoding, regarding the video data, video data of parallel 8 bits×3 channels into serial 10 bits×3 channels, and regarding audio data, audio data of parallel 4 bits into serial 10 bits. The receiver  408  decodes the video data and audio data transmitted from the transmitter  407  and converts the video data of serial 10 bits into parallel 8 bits, and the audio data of serial 10 bits into parallel 4 bits, and reproduces the video data and the audio data in the baseband. 
     The transmitter  407  and the receiver  408  are connected by is the Transition Minimized Differential Signaling (TMDS). The TMDS is a serial high-speed digital transmission method, and is a balanced (differential) type serial transmission method using three pairs of data signal lines and a pair of clock signal lines, and judges a signal by potential difference between two signal lines. 
     In addition, the HDMI cable includes a CEC signal line, a DDC signal line, an HPD signal line and a 5V line. The CEC  415  is an appliance control line Consumer Electronics Control (CEC), and transmits control signals for consumer appliances. The DDC  416  is a Display Data Channel (DDC) and transmits control signals for obtaining EDID information in the video and audio reproduction device such as a TV. The HPD  417  is a Hot Plug Detect (HPD), and is connected to a 5V terminal of the HDMI terminal in the video and audio reproduction device  412  via a 1KΩ resistor. The HPD is a signal for notifying a possible timing for obtaining the EDID information, when the video and audio output device  410  obtains EDID information of the video and audio reproduction device  412  using the DDC communication. The control of the timing when the EDID is available is performed by a HPD control unit (for example, a microcomputer  418 ) in the video and audio reproduction device  412 . The 5V  414  is a 5V line, and supplies a voltage of 5V to the video and audio reproduction device  412 . 
     [Non-patent reference 1] “High-Definition Multimedia Interface Specification Version 1.1” (May 20, 2004). 
     DISCLOSURE OF INVENTION 
     Problems that Invention is to Solve 
     A DVD recorder and an AV amplifier fixed indoor are mainly used as the video and audio output device  410 . However, in recent years, the image quality of portable devices such as a camcorder and the like has been improved, and there has been a request for transmitting, via HDMI, image data and audio data on which image data of high image quality and audio data of high sound quality is recorded and reproduced for viewing on TV. 
     However, in a portable device such as a camcorder, for example, without a fixed service space and on which the HDMI cable is frequently inserted/removed, when a piece of metal and the like fall in the HDMI terminal and the 5V terminal, causing other terminals to be short-circuited, there is a possibility that a critical problem which destroys the device arises. 
     The present invention is conceived in order to solve the above problem and it is an object of the present invention to provide a video and audio output device which stops 5V output from the 5V terminal of the HDMI terminal when the video and audio output device having an HDMI function is not connected to the video and audio reproduction device via the HDMI cable. 
     Means to Solve the Problems 
     In order to solve the above problem, the video and audio output device according to the present invention includes: a first terminal which outputs a video and audio signal to an external device via a first signal line; a second terminal which supplies voltage to the external device via a second signal line; a voltage supply unit operable to apply the voltage to the second terminal; a switch unit which is located between the second terminal and the voltage supply unit, and is for switching the application of the voltage from the voltage supply unit to the second terminal between ON and OFF; a connection judging unit operable to judge a connection status between the first terminal and the external device; and a control unit operable to control the application of the voltage from the voltage supply unit to the second terminal by switching the switch unit between ON and OFF, based on a result of the judgment by the connection judging unit. 
     EFFECTS OF THE INVENTION 
     According to the video and audio output device of the present invention, since voltage is not applied to a voltage terminal when the voltage terminal is not connected to the video and audio reproduction device, it is possible to prevent the damage of an device even when metal pieces and the like falls in a connector, causing the voltage terminal of a connector and other terminal to be short-circuited. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a video and audio output device according to an embodiment of the present invention. 
         FIG. 2  is a flowchart showing a flow of the video and audio output device according to an embodiment of the present invention. 
         FIG. 3  is a chart showing an algorithm of the ON/OFF setting unit in an embodiment of the present invention. 
         FIG. 4  is a timing chart of the video and audio output device according to the first embodiment of the present invention. 
         FIG. 5  is a block diagram showing a conventional video and audio output device. 
     
    
    
     NUMERICAL REFERENCES 
     
         
           101  ON/OFF control signal 
           102  SW 
           103  Output port 
           401  Resistor 
           402  5V terminal 
           403  HPD terminal 
           404  1KΩ resistor 
           405  5V power supply 
           406  Microcomputer 
           407  HDMI transmitter 
           408  HDMI receiver 
           410  Video and audio output device 
           411  HDMI cable 
           412  Video and audio reproduction device 
           413  TMDS bias detection signal 
           414  5V 
           415  CEC signal 
           416  DDC signal 
           417  HPD signal 
           418  Microcomputer 
           419  Bias detection circuit 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of the present invention is explained in detail with reference to the drawings. 
       FIG. 1  is a block diagram showing a video and audio output device according to an embodiment of the present invention. In  FIG. 1 , the components in the block diagram of the conventional example shown in  FIG. 5  are shown using the same reference numerals and the descriptions are omitted. 
     In  FIG. 1 , a bias detection circuit  419  detects a bias level of the TMDS signal. An SW unit  102  is an SW circuit to short-circuit or open the 5V power supply  405  and the 5V terminal of the HDMI terminal. The ON/OFF control signal  101  is a signal outputted from the output port  103  of the microcomputer, and the SW unit  102  is controlled using the signal. 
     Next, operations of the video and audio output device  410  according to the present invention are described with reference to the flowchart shown in  FIG. 2 . 
     The video and audio output device  410  confirms that the video and audio output device  410  is connected to the video and audio reproduction device  412  via the HDMI cable  411  (Step  100 ). As a method to confirm the connection, a bias level of the TMDS signal or the HPD signal line is checked. Here, a method to check the bias level of the TMDS signal is described. The TMDS signal line is a current source of which the drain is open on the transmitter side, and is a differential receiver on the receiver side, and a positive side and a negative side of difference end in offset, at 50Ω and 3.3V respectively. If the power source of 3.3 V for TMDS is supplied on the receiver  408  side, it is easy to judge whether or not bias is applied on the transmitter side by the bias detection circuit  419  which compares the TMDS signal by a comparator and the like. The information regarding the detection obtained from the bias detection circuit  419  is inputted to the input port  414  of the microcomputer  406 , and the video and audio output device  410  confirms that the video and audio output device  410  is connected to the video and audio reproduction device  412  with the HDMI cable  411 . 
     Next, the video and audio output device  410  executes the TMDS bias detection program on the microcomputer  406  and performs switch setting (Step  200 ).  FIG. 3  is a diagram showing an algorithm of the ON/OFF setting unit. Step  202  is a judgment process, and monitors a level of the input port  414  in the microcomputer  406 . When the input port  414  is set as High, it is judged that there is a TMDS bias and the process moves to Step  203 . When the input port  414  is set as Low, it is judged that there is no TMDS bias, and the process moves to Step  204 . Step  203  is a process that the output port  103  of the microcomputer  406  set the ON/OFF signal  101  as High. Step  204  is a process that the output port  103  of the microcomputer  406  set the ON/OFF signal  101  as Low. 
     Next the SW unit  102  controls voltage supply from the 5V power source  405  based on the inputted ON/OFF control signal  101  (Step  300 ). The SW unit  102  is short circuited when the ON/OFF control signal  101  is set as High, and supplies 5V from the 5V power source  405  to the 5V terminal  402  in the 5V power supply  405 . In addition, the SW unit  102  is open when the ON/OFF control signal  101  is Low, and the 5V supplied from the 5V power source  405  is not supplied to the 5V terminal  402  of the HDMI terminal and the 5V terminal  402  is in high impedance. 
     Next, the state of each signal in the video and audio output device  410  is explained with reference to the timing chart shown in  FIG. 4 . When the video and audio output device  410  and the video and audio reproduction device  412  are connected with the HDMI cable  411 , the TMDS signal is biased. The bias detection circuit  419  set the level of the TMDS bias detection signal  413  as High. When the video and audio reproduction device  412  is not available for HDMI input, more specifically, when the video and audio output device  410  is not connected to the video and audio reproduction device  412  with the HDMI cable  411 , or when the main power supply of the video and audio reproduction device  412  is switched off, the TMDS signal is not biased. The bias detection circuit  419  set the level of the TMDS bias detection signal  413  as low. The bias detection signal  413  is inputted to the input port of the microcomputer  406 . The microcomputer  406  executes the algorithm of the ON/OFF setting unit shown in  FIG. 3 , and outputs the ON/OFF control signal  101  to the output port  103 . The ON/OFF control signal  101  is a signal for controlling the SW unit  102  from the output port of the microcomputer. When the ON/OFF control signal  101  is in High level, the SW unit  102  is short-circuited and 5V from the 5V power source  405  is supplied to the 5V terminal  402  of the HDMI terminal. In addition, the SW unit  102  is open when the ON/OFF control signal  101  is Low, and 5V supplied from the 5V power source  405  is not supplied to the 5V terminal  402  and thus the 5V terminal  402  is in high impedance. 
     As described above, by detecting whether the TMDS signal is biased or not, and based on the detection result of the bias of the TMDS signal, 5V supply of 5V terminal in the HDMI terminal is controlled. With this, when the video and audio output device  410  is not connected to the video and audio reproduction device  412  with the HDMI cable, it is possible to stop the 5V supply to the 5V terminal of the HDMI terminal, and damage to a device caused by metal pieces and others fallen into the HDMI terminal can be prevented even when the 5V terminal of the HDMI terminal and other terminal is short-circuited. 
     Furthermore, by stopping the supply of 5V, the power consumption in the video and audio reproduction device  412  can be controlled, and thus it is possible to suppress the battery consumption and extend battery life when it is applied to a video and audio reproduction device such as a camcorder and the like. 
     Note that, in the above embodiment, a method to execute the algorithm in  FIG. 3  using a microcomputer is explained, however, the bias detection signal  413  may be directly used as an ON/OFF signal of the SW unit  102 . 
     In addition, it is possible to apply the DVD recorder, a device such as a camcorder, or a given AV device as a video and audio output device. 
     INDUSTRIAL APPLICABILITY 
     The video and audio output device according to the present invention is capable of preventing the HDMI terminal not to apply 5V when the video and audio output device is not connected to the HDMI cable, and is useful for a video and audio output device for transmitting the video data and audio data based on the High Definition Multimedia Interface (HDMI) standard, and more particularly to portable devices such as a camcorder and the like with frequent insertion/removal of the HDMI cable and without a fixed place for use.