Abstract:
A high definition multimedia interface (HDMI) device and an output control method thereof are disclosed. The HDMI device includes a moving picture experts group (MPEG) decoder for decoding an MPEG stream, and an HDMI transmitter for transmitting an output of the MPEG decoder to a display device. The method comprises determining whether an HDMI cable has been connected between the HDMI device and the display device, and inhibiting digital data from being output from the MPEG decoder to the HDMI transmitter if the HDMI cable has not been connected.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2005-21918, filed on Mar. 16, 2005 in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a high definition multimedia interface (HDMI) device and an output control method thereof. More particularly, the present invention relates to an apparatus and method in which digital data is output from the HDMI device to a display device only when a HDMI cable is connected there between.  
         [0004]     2. Description of the Related Art  
         [0005]     Recently, digital versatile discs (DVDs) have been introduced as a recording media that records and reproduces high quality video. Additionally, digital televisions (TVs) have been developed that display high resolution video. By virtue of their proliferation in the market, an increasing number of consumers have interconnected and used various DVD devices (for example, a DVD player, a DVD recorder, and so on) that record and/or reproduce video with DVDs and digital TVs. Accordingly, the digital visual interface (DVI) and high definition multimedia interface (HDMI) have been standardized as a digital interface for the transfer of data between a DVD device and a digital TV.  
         [0006]     Devices that transfer video and audio data to display devices, such as digital TVs, using HDMI are typically called HDMI devices. Examples of HDMI devices include set-top boxes, video tape recorders (VTRs), game machines, and various DVD devices. A conventional HDMI device is the DVD device disclosed in Korean Patent Laid-open Publication No. 10-2004-0071247. This DVD device comprises a moving picture experts group (MPEG)-2 decoder for decoding a MPEG-2 stream, a transmitter for encoding data to be transmitted over a plurality of channels, and a microcontroller for controlling the transmitter and MPEG-2 decoder.  
         [0007]     This conventional HDMI device is adapted to encode video and audio data that is output from the MPEG-2 decoder using transition minimized differential signaling (TMDS). Further, the conventional HDMI device is adapted to transmit the encoded data to a display device using a HDMI link.  
         [0008]     However, the above-mentioned conventional HDMI device has a drawback in that there is an increase in electromagnetic compatibility (EMC) caused by noise that occurs when the HDMI device is powered on and a HDMI link between the HDMI device and the display device is not being used. The source of the noise is the digital video and audio data being output from the MPEG-2 decoder to the transmitter.  
         [0009]     EMC is an umbrella term that brings together two concepts, electromagnetic interference (EMI) and electromagnetic susceptibility (EMS). EMI is the level of radio frequency (RF) interference at a device caused by the operation of another device. EMS is the level of resistance a device has to all ambient RF energy (static electricity, surge, and so on).  
         [0010]     Accordingly, there is a need for an improved HDMI device including an output control method that does not increase electromagnetic compatibility (EMC) of a HDMI device when the HDMI device is powered on and is not using a HDMI link.  
       SUMMARY OF THE INVENTION  
       [0011]     An aspect of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method for controlling an output of a high definition multimedia interface (HDMI) device, the HDMI device including a moving picture experts group (MPEG) decoder for decoding an MPEG stream, and an HDMI transmitter for transmitting an output of the MPEG decoder to a display device. The method comprises determining whether a signal transmission line has been connected between the HDMI device and the display device and inhibiting digital data from being output from the MPEG decoder to the HDMI transmitter if the signal transmission line has not been connected.  
         [0012]     Preferably, the method further comprises allowing the digital data to be outputted from the MPEG decoder to the HDMI transmitter if the signal transmission line has been connected.  
         [0013]     The signal transmission line may include a plurality of channels for transmitting the digital data.  
         [0014]     The determination may be performed using a signal on a hot plug detect (HPD) line connected between the HDMI device and the display device.  
         [0015]     Preferably, the determination includes determining the HDMI device and the display device to have been interconnected via the signal transmission line if the signal on the HPD line is high, and the HDMI device and the display device not to have been interconnected via the signal transmission line if the signal on the HPD line is low.  
         [0016]     The digital data may include video data, a horizontal synchronous signal, a vertical synchronous signal, and audio data.  
         [0017]     In accordance with another aspect of the invention, there is provided an HDMI device comprising an MPEG decoder for decoding an MPEG stream, an HDMI transmitter for transmitting an output of the MPEG decoder to a display device using a signal transmission line, and a controller for inhibiting digital data from being output from the MPEG decoder to the HDMI transmitter if the HDMI device and the display device are not interconnected via the signal transmission line.  
         [0018]     The MPEG decoder may include an output control block for controlling the output of the digital data in response to a control command from the controller.  
         [0019]     The digital data may include video data, a horizontal synchronous signal, a vertical synchronous signal, and audio data, and the output control block may ground the video data, horizontal synchronous signal, vertical synchronous signal and audio data so as to inhibit the digital data from being output.  
         [0020]     The signal transmission line may include a plurality of channels for transmitting the digital data.  
         [0021]     The controller may determine whether the HDMI device and the display device have been interconnected via the signal transmission line, using a signal on an HPD line connected between the HDMI transmitter and the display device.  
         [0022]     Other objects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The above and other objects, features, and advantages of certain embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:  
         [0024]      FIG. 1  is a view showing a connection between a DVD player, an exemplary HDMI device according to an embodiment of the present invention, and a digital TV via an HDMI cable;  
         [0025]      FIG. 2  is a detailed block diagram of the DVD player and digital TV of  FIG. 1 ;  
         [0026]      FIG. 3  is a block diagram illustrating, in detail, various signals output from an MPEG-2 decoder in the DVD player of  FIG. 2 ; and  
         [0027]      FIG. 4  is a flow chart illustrating a method for controlling the output of the MPEG-2 decoder in the DVD player, an exemplary HDMI device according to an embodiment of the present invention. 
     
    
       [0028]     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures.  
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0029]     The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.  
         [0030]      FIG. 1  shows a connection between a DVD player  10 , an exemplary HDMI device (or source device), and a digital TV  20  via an HDMI cable  30 . In other words, the DVD player  10  is HDMI-linked with the digital TV  20  via the HDMI cable  30 .  
         [0031]      FIG. 2  shows a DVD player  10  comprising an MPEG-2 decoder  11 , an HDMI transmitter  13 , an encryption read only memory (ROM)  15 , and a transmission controller  16 . The MPEG-2 decoder  11  is adapted to receive and decode an MPEG-2 stream reproduced from a DVD drive (not shown) or delivered from a set-top box (not shown). The HDMI transmitter  13  is adapted to receive transition minimized differential signaling (TMDS)-encoded digital data output from the MPEG-2 decoder  11  and transmit the encoded digital data to the digital TV  20  through the HDMI cable  30 .  
         [0032]     The encryption ROM  15  is adapted to store a key value and an identification bit which are used for High bandwidth Digital Content Protection (HDCP) encryption of the data to be transmitted to the digital TV  20 . The transmission controller  16  is adapted to control the MPEG-2 decoder  11  and the HDMI transmitter  13 . The transmission controller  16  is further adapted to perform  12 C communication with the HDMI transmitter  13 .  
         [0033]     The digital TV  20  of  FIG. 2  is an exemplary display device (or Sync device), and includes an HDMI receiver  23 , a video processor  22 , a display  21 , an audio processor  29 , an audio output unit  28 , an extended display identification data (EDID) ROM  27 , an encryption ROM  25  and a reception controller  26 . The HDMI receiver  23  is adapted to receive and TMDS-decode the digital data transmitted from the HDMI transmitter  13 . The decryption ROM  25  is adapted to store a key value and an identification bit which are used for High bandwidth Digital Content Protection (HDCP) decryption of the data to be received from the DVD player  10 . The video processor  22  is adapted to process digital video data sent from the HDMI receiver  23  and to send the resulting digital video data DigVideo or analog video data AnVideo to the display  21 . The audio processor  29  is adapted to process digital audio data sent from the HDMI receiver  23  and to send the resulting digital audio data DigAudio to the audio output unit  28 . The display  21  is adapted to output the video data from the video processor  22  as video viewable by the user. The audio output unit  28  is adapted to output the audio data from the audio processor  29  as audible sound.  
         [0034]     The EDID ROM  27  is adapted to store extended display identification data (EDID), which is display characteristic information data containing a manufacturer&#39;s name, specifications, supported resolutions, color formats, and so on. This EDID is stored in the EDID ROM  27  at the time of the digital TV&#39;s manufacturing. The EDID ROM  27  is also connected with the transmission controller  16  via a display data channel (DDC) line  41 , so that the transmission controller  16  can read the EDID from the EDID ROM  27  over the DDC line  41 . The reception controller  26  is adapted to control the above components of the digital TV  20  and perform  12 C communication with the HDMI receiver  23 .  
         [0035]     The HDMI transmitter  13  and the HDMI receiver  23  are interconnected via the HDMI cable  30 , which includes a plurality of channels  43  and a hot plug detect (HPD) line  42 . The plurality of channels  43  are signal lines for transmission of digital video and digital audio data, and include three data transmission channels CH 0 , CH 1  and CH 2 , and one clock channel CHC. The HPD line  42  is provided to enable the transmission controller  16  to determine whether the DVD player  10  and the digital TV  20  are interconnected via the HDMI cable  30 . If the digital TV  20  is connected with the DVD player  10  via the HDMI cable  30 , a high signal is applied to the HPD line  42  to indicate the digital TV&#39;s  20  presence. On the contrary, if the digital TV  20  is not connected with the DVD player  10  via the HDMI cable  30 , typically a low signal is applied to the HPD line  42 . The transmission controller  16  checks a voltage on the HPD line  42  in order to determine if the digital TV  20  is HDMI-linked with the DVD player  10 . Of course any suitable signal, including a current or frequency, could be used on the HPD line  42  to indicate the digital TV&#39;s  20  presence. Preferably, the digital TV  20  is considered HDMI-linked with the DVD player  10  if the voltage on the HPD line  42  is high, such as 2.2-5.05V. Further, the digital TV  20  is considered not HDMI-linked with the DVD player if the voltage on the HPD line  42  is low, such as 0-0.4V.  
         [0036]     An output control block  12  is provided in the MPEG-2 decoder  11 , as shown in  FIG. 3 , to control the output of the MPEG-2 decoder  11 . The output control block  12  is adapted to control the output of the MPEG-2 decoder  11  in response to a control command from the transmission controller  16 . The digital data which is output from the MPEG-2 decoder  11  to the HDMI transmitter  13  includes video data VDATA, such as RGB data, a horizontal synchronous signal HSYNC, a vertical synchronous signal VSYNC, and audio data IEC958. The output control block  12 , under the control of the transmission controller  16 , either sends digital data output from the MPEG-2 decoder to the HDMI transmitter  13  or grounds the signal lines so that there is no output signal.  
         [0037]     The HDMI transmitter  13  includes a TMDS encoder  14  for TMDS-encoding the digital data output from the MPEG-2 decoder  11 . The HDMI receiver  23  includes a TMDS decoder  24  for TMDS-decoding the digital data encoded and transmitted by the HDMI transmitter  13 .  
         [0038]     Preferably, the TMDS encoder  14  converts parallel 8-bit 3-channel VDATA, HSYNC and VSYNC video data into serial 10-bit 3-channel video data, and parallel 4-bit audio data IEC958 into serial 10-bit audio data, respectively. The converted digital data is then transmitted to the HDMI receiver  23  over the respective channels  43  of the HDMI cable  30 . Preferably, the TMDS decoder  24  restores the serial 10-bit video data and serial 10-bit audio data transmitted over the respective channels  43  back into parallel 8-bit video data and parallel 4-bit audio data, respectively.  
         [0039]     A method for controlling the output of the DVD player, an exemplary HDMI device, according to an embodiment of the present invention, will hereinafter be described with reference to  FIG. 4 . In an embodiment of the present invention, when the DVD player  10  is powered on, and is not transmitting digital data to a display device, such as the digital TV  20 , the data output from the MPEG-2 decoder  11  is inhibited to reduce EMC. To this end, the transmission controller  16  determines whether the DVD player  10  is powered on ( 50 ), and then proceeds to the next step only when the DVD player  10  is powered on.  
         [0040]     If it is determined at step  50  that the DVD player  10  is powered on, the transmission controller  16  performs I2C communication with the HDMI transmitter  13  to check a signal on the HPD line  42  (or a voltage on the HPD line  42 ) so as to determine whether the DVD player  10  and the digital TV  20  have been interconnected via the HDMI cable  30  ( 52 ). The transmission controller  16  then determines whether the signal on the HPD line  42  is ‘high’ ( 54 ). Preferably, the voltage on the HPD line  42  is considered ‘high’ when the voltage is about 2.4-5.05V.  
         [0041]     When the signal on the HPD line  42  is ‘high’, the transmission controller  16  recognizes that the DVD player  10  can transmit digital data to the digital TV  20  because it has been connected to the digital TV  20  via the HDMI cable  30 . Accordingly, the transmission controller  16  sends a control command to the output control block  12  via a  12 C communication therewith such that the MPEG-2 decoder  11  outputs video data VDATA, a horizontal synchronous signal HSYNC, a vertical synchronous signal VSYNC, and audio data IEC958 ( 56 ). If these signals are output from the MPEG-2 decoder  11 , the HDMI transmitter  13  TMDS-encodes those signals and transmits the resulting signals to the HDMI receiver  23  ( 58 ).  
         [0042]     On the other hand, if it is determined at step  54  that the signal on the HPD line  42  is ‘low’, the transmission controller  16  recognizes that the DVD player  10  and the digital TV  20  have not been interconnected via the HDMI cable  30 . Preferably, a voltage on HPD line  42  is considered ‘low’ when the voltage is about 0-0.4V. Accordingly, the transmission controller  16  sends a control command to the output control block  12  via a  12 C communication therewith such that the output control block  12  grounds video data VDATA, a horizontal synchronous signal HSYNC, a vertical synchronous signal VSYNC, and audio data IEC958 ( 60 ).  
         [0043]     Although the VDATA video data and the IEC958 audio data are shown in  FIG. 3  to be separated from each other for the convenience of description, it will be understood that the audio data IEC958 is typically interleaved in the video data VDATA. In this regard, when the video data VDATA is grounded, the audio data IEC958 is grounded as well. If the various digital data lines are grounded in this mainer, the MPEG-2 decoder  11  is prevented from outputting digital data and thus permits DVD player  10  to output only analog signals, such as a composite signal, an S-VIDEO signal, or a component signal. By only outputting analog signals, a reduction in the occurrence of noise results.  
         [0044]     Although the DVD player has been disclosed as an example of a HDMI device, the present invention is applicable to all devices with HDMI outputs, such as a set-top box, a VTR or a game machine.  
         [0045]     As is apparent from the above description, according to an embodiment of the present invention, an MPEG-2 decoder outputs digital data only when an HDMI device (such as, a source device) and a display device (such as, a Sync device) are interconnected via an HDMI cable. It is therefore possible to reduce EMC.  
         [0046]     While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.