Abstract:
A digital image system which transmits digital image data, and more particularly, to a digital image system in a high definition multimedia interface (HDMI) format or a digital visual interface (DVI) format.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application is a national phase of International Application No. PCT/KR2008/000013, entitled “DIGITAL IMAGE SYSTEM TRANSMITTING DIGITAL IMAGE DATA”, which was filed on Jan. 2, 2008, and which claims priority of Korean Patent Application No. 10-2007-0003408, filed on Jan. 11, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention generally relates to a digital image system which transmits digital image data, and more particularly, to a digital image system in a high definition multimedia interface (HDMI) format or a digital visual interface (DVI) format. 
     2. Background Art 
     Referring to  FIG. 1 , a digital image system in a basic high definition multimedia interface (HDMI) format includes a host device  11 , a display device  12 , and electric cables. The electric cables are connected between input/output terminals T H1  through T H14  of the host device  11  and input/output terminals T D1  through T D14  of the display device  12 . 
     The host device  11  includes an HDMI transmission unit  111  and a graphic control unit  112 . The display device  12  includes a serial electrically erasable and programmable read only memory (EEPROM)  122  and an HDMI reception unit  121 . 
     The HDMI transmission unit  111  in the host device  11  converts audio data S AUD , a clock signal S CS , and digital image data S VID  into transition minimized differential signaling (TMDS) signals in an HDMI format and outputs the TMDS signals to the display device  12 . 
     More specifically, the audio data S AUD  and the digital image data S VID  are processed by the HDMI transmission unit  111  and are output as red signals S R+  and S R−  of 2 channels, green signals S G+  and S G−  of 2 channels, and blue signals S B+  and S B−  of 2 channels. The clock signal S CS  is processed by the HDMI transmission unit  111  and is output as clock signals CLK+ and CLK− of 2 channels. 
     The serial EEPROM  122  in the display device  12  stores extended display identification data (EDID) of the display device  12  and provides the EDID to the graphic control unit  112  of the host device  11  according to an inter-integrated circuit (I 2 C) communication protocol. 
     In I2C communication, the graphic control unit  112  exchanges data signals SDA with the serial EEPROM  122  while transmitting a clock signal SCL to the serial EEPROM  122 . The graphic control unit  112  provides a power-supply potential of +5V and a ground potential GND to the serial EEPROM  122  for an operation of the serial EEPROM  122 . The display device  12  applies a hot plug detect (HPD) signal voltage HPD to the graphic control unit  112  and thus the graphic control unit  112  recognizes that the graphic control unit  112  is connected with the display device  12 . Reserved terminals T H14  and T D14  that are not used are referred to as no-connection (NC) terminals. 
     The graphic control unit  112  in the host device  11  controls an operation of the HDMI transmission unit  111  according to the EDID. 
     The HDMI reception unit  121  in the display device  12  restores the audio data S AUD , the clock signal S CS , and the digital image data S VID  from the TMDS signals in the HDMI format, which have been received from the host device  11 . 
       FIG. 2  illustrates a digital image system in a general digital visual interface (DVI) format. In  FIGS. 1 and 2 , like reference numerals refer to like elements. Hereinafter, only differences between the digital image system illustrated in  FIG. 2  and the digital image system illustrated in  FIG. 1  will be described. Referring to  FIG. 1 , the digital image system in a basic DVI format includes a host device  21 , a display device  22 , and electric cables. The electric cables are connected between input/output terminals T H1  through T H14  of the host device  21  and input/output terminals T D1  through T D14  of the display device  22 . 
     The host device  21  includes a TMDS transmission unit  211  and a graphic control unit  212 . The display device  22  includes a serial EEPROM  222  and a TMDS reception unit  221 . 
     The TMDS transmission unit  211  in the host device  11  converts a clock signal S CS  and digital image data S VID  into TMDS signals in a DVI format and outputs the TMDS signals to the display device  22 . 
     The serial EEPROM  222  in the display device  22  stores EDID of the display device  22  and provides the EDID to the graphic control unit  212  of the host device  21  according to the I 2 C communication protocol. 
     The graphic control unit  212  of the host device  21  controls an operation of the TMDS transmission unit  211  according to the EDID. 
     The TMDS reception unit  221  in the display device  22  restores the clock signal S CS  and the digital image data S VID  from the TMDS signals in the DVI format, which have been received from the host device  21 . 
     In the digital image system illustrated in  FIG. 1  or  2 , the maximum length between the host device  11  or  21  and the display device  12  or  22  is limited to about 10 m. When a distance between the host device  11  or  21  and the display device  12  or  22  is long, a transmission/reception reinforcement device such as an optical cable module, a repeater, or an equalizer is required. 
     In a digital image system where the host device  11  or  21  transmits digital image data to the display device  12  or  22  using the transmission/reception reinforcement device, transmission of the digital image data is not smooth if an external power supply of the transmission/reception reinforcement device drops and the transmission may not be performed at all if the external power supply is interrupted. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a digital image system in a basic high definition multimedia interface (HDMI) format; 
         FIG. 2  illustrates a digital image system in a basic digital visual interface (DVI) format; 
         FIG. 3  illustrates an optical cable module as a transmission/reception reinforcement device interposed between a host device illustrated in  FIG. 1  or  2  and a display device illustrated in  FIG. 1  or  2  according to a first embodiment of the present invention; 
         FIG. 4  illustrates an internal circuit of a first power-supply switching unit or a second power-supply switching unit included in the transmission/reception reinforcement device illustrated in  FIG. 3 ; 
         FIG. 5  illustrates an optical cable module as a transmission/reception reinforcement device interposed between a host device illustrated in  FIG. 1  or  2  and a display device illustrated in  FIG. 1  or  2  according to a second embodiment of the present invention; 
         FIG. 6  illustrates an optical cable module as a transmission/reception reinforcement device interposed between a host device illustrated in  FIG. 1  or  2  and a display device illustrated in  FIG. 1  or  2  according to a third embodiment of the present invention; 
         FIG. 7  illustrates an optical cable module as a transmission/reception reinforcement device interposed between a host device illustrated in  FIG. 1  or  2  and a display device illustrated in  FIG. 1  or  2  according to a fourth embodiment of the present invention; and 
         FIG. 8  illustrates an optical cable module as a transmission/reception reinforcement device interposed between a host device illustrated in  FIG. 1  or  2  and a display device illustrated in  FIG. 1  or  2  according to a fifth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
     The present invention provides a digital image system in which a host device transmits digital image data to a display device using a transmission/reception reinforcement device, whereby smooth transmission of the digital image data can be maintained even when an external power supply of the transmission/reception reinforcement device drops or is interrupted. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a digital image system including a host device, a transmission/reception reinforcement device, and a display device. 
     The host device transmits digital image data to the display device through the transmission/reception reinforcement device. 
     The transmission/reception reinforcement device includes a first power-supply switching unit and/or a second power-supply switching unit. 
     Each of the first power-supply switching unit and the second power-supply switching unit includes an external power-supply input terminal, an internal power-supply input terminal, a power-supply output terminal, and a switch. 
     A separate external power-supply voltage is input to the external power-supply input terminal. 
     The internal power-supply input terminal is connected with one internal power-supply line out of communication lines between the host device and the display device. 
     The external power-supply voltage from the external power-supply input terminal or an internal power-supply voltage from the internal power-supply input terminal is output from the power-supply output terminal. 
     The switch enters an ON state when the external power-supply voltage from the external power-supply input terminal becomes lower than a predetermined voltage. 
     The external power-supply voltage is applied to the power-supply output terminal when the switch is in an OFF state and the internal power-supply voltage from the internal power-supply input terminal is applied to the power-supply output terminal when the switch is in the ON state. 
     Advantageous Effects 
     According to the digital image system according to the present invention, when the external power-supply voltage is applied, the transmission/reception reinforcement device operates by means of the external power-supply voltage. When the external power-supply voltage becomes lower than a predetermined voltage or is not applied, the transmission/reception reinforcement device operates by means of an internal power-supply voltage applied through one internal power-supply line outside of communication lines between the host device and the display device. 
     Therefore, smooth transmission of digital image data can be maintained in spite of dropping or interruption of an external power-supply of the transmission/reception reinforcement device. 
     BEST MODE 
       FIG. 3  illustrates an optical cable module as a transmission/reception reinforcement device interposed between a host device  11  or  21  illustrated in  FIG. 1  or  2  and a display device  21  or  22  illustrated in  FIG. 1  or  2  according to a first embodiment of the present invention. In  FIGS. 1 through 3 , like reference numerals refer to like elements. A digital image system illustrated in  FIG. 1  or  2  is also used in the first embodiment of the present invention and thus will not be described in detail. 
     Referring to  FIGS. 1 through 3 , a transmission/reception reinforcement device included in the digital image system according to the first embodiment of the present invention is an optical cable module including optical cables T H15 -T D15  through T H21 -T D21 , a transmission unit  31 , and a reception unit  32 . In  FIG. 3 , reference numerals L H1  through L H6  and L D1  indicate light emitting diodes and P D1  through P D6  and P H1  indicate light receiving diodes. 
     The transmission unit  31  operates when supplied with a power-supply voltage V CC  from a first power-supply switching unit  312 , converts digital image data S R+ through CLK−, an I 2 C communication clock signal SCL, and I 2 C communication data SDA, which have been received from the host device  11  or  21 , into optical signals S R  through SDA R  by means of a light emission driving unit  311  for output to the optical cables T H15 -T D15  through T H20 -T D20 , and converts I 2 C communication data SDA L  received from the optical cable T H21 -T D21  into an electric signal for output to the host device  11  or  21 . 
     The reception unit  32  operates when supplied with the power-supply voltage V CC  from a second power-supply switching unit  322 , converts the optical signals S R  through SDA R  received from the optical cables T H15 -T D15  through T H20 -T D20  into the digital image data S R+  through CLK−, the I 2 C communication clock signal SCL, and the I 2 C communication data SDA by means of a light reception amplification unit  321  for output to the display device  12  or  22 , and converts the I 2 C communication data SDA received from the display device  12  or  22  into the I 2 C communication data SDA L  for output to the optical cable T H21 -T D21 . 
       FIG. 4  illustrates an internal circuit of the first power-supply switching unit  312  or the second power-supply switching unit  322  included in the transmission/reception reinforcement device illustrated in  FIG. 3 . 
     Referring to  FIGS. 1 through 4 , the first power-supply switching unit  312  or the second power-supply switching unit  322  includes an external power-supply input terminal V EXT , an internal power-supply input terminal HPD, a power-supply output terminal V CC , and a p-channel field effect transistor TR P  as a switch. 
     The external power-supply input terminal V EXT , to which a separate external power-supply voltage is input, is connected to an anode of a first diode SPRD L  and a gate of the p-channel field effect transistor TR P . A cathode of the first diode SPRD L  is connected to the power-supply output terminal V CC . The internal power-supply input terminal HPD is connected to a communication line T H13 -T D13  to which an HPD signal voltage received from the display device  12  or  22  is applied. The internal power-supply input terminal HPD is also connected to a source of the p-channel field effect transistor TR P . A drain of the p-channel field effect transistor TR P  is connected to an anode of a second diode SPRD U . A cathode of the second diode SPRD U  is connected to the power-supply output terminal V CC . 
     The p-channel field effect transistor TR P  enters an ON state when an external power-supply voltage from the external power-supply input terminal V EXT  becomes lower than a predetermined voltage. When the p-channel field effect transistor TR P  is in an OFF state, the external power-supply voltage is applied to the power-supply output terminal V CC . When the p-channel field effect transistor TR P  is in the ON state, an internal power-supply voltage from the internal power-supply input terminal HPD is applied to the power-supply output terminal V CC . 
     In other words, when the external power-supply voltage is applied, the transmission/reception reinforcement device illustrated in  FIG. 3  operates by means of the external power-supply voltage. When the external power-supply voltage becomes lower than the predetermined voltage or is not applied, the transmission/reception reinforcement device operates by means of the HPD signal voltage applied to one of the communication lines between the host device  11  or  21  and the display device  12  or  22 . 
     Thus, smooth transmission of digital image data can be maintained in spite of dropping or interruption of an external power supply of the transmission/reception reinforcement device illustrated in  FIG. 3 . 
     MODE OF THE INVENTION 
       FIG. 5  illustrates an optical cable module as a transmission/reception reinforcement device interposed between the host device  11  or  21  illustrated in  FIG. 1  or  2  and the display device  21  or  22  illustrated in  FIG. 1  or  2  according to a second embodiment of the present invention. In  FIG. 5 , internal circuits of a first power-supply switching unit  512  and a second power-supply switching unit  522  are the same as those illustrated in  FIG. 4 . 
     In  FIGS. 3 and 5 , like reference numerals refer to like elements. A difference between the first embodiment illustrated in  FIG. 3  and the second embodiment illustrated in  FIG. 5  is an internal power-supply line T H25 -T D25  connected with an internal power-supply input terminal NC. In other words, the internal power-supply line T H25 -T D25  connected with the internal power-supply input terminal NC is a reserved line between a reserved terminal T H14  illustrated in  FIG. 1  or  2  at the side of the host device  11  or  21  and a reserved terminal T D14  illustrated in  FIG. 1  or  2  at the side of the display device  12  or  22 . An internal power-supply voltage of +5V is applied to the reserved line NC through the reserved terminal T D14  at the side of the display device  12  or  22 . 
       FIG. 6  illustrates an optical cable module as a transmission/reception reinforcement device interposed between the host device  11  or  21  illustrated in  FIG. 1  or  2  and the display device  12  or  22  illustrated in  FIG. 1  or  2  according to a third embodiment of the present invention. In  FIGS. 3 and 6 , like reference numerals refer to like elements. In  FIG. 6 , internal circuits of a first power-supply switching unit  612  and a second power-supply switching unit  622  are the same as those illustrated in  FIG. 4 . Hereinafter, only a difference between the first embodiment illustrated in  FIG. 3  and the third embodiment illustrated in  FIG. 6  will be described in detail. 
     The transmission/reception reinforcement device of the digital image system according to the third embodiment of the present invention is an optical cable module including optical cables T H15 -T D15  through T H18 -TD 18 , a transmission unit  61 , and a reception unit  62 . 
     The transmission unit  61  operates when supplied with a power-supply voltage V CC  from the first power-supply switching unit  612 , converts digital image data S R+  through CLK− of 8 channels, which have been received from the host device  11  or  21 , into optical signals S R  through CLK by means of a light emission driving unit  611  for output to the optical cables T H15 -T D15  through T H18 -T D18 , and buffers an I 2 C communication clock signal SCL and I 2 C communication data SDA, which have been received from the host device  11  or  21 , by means of an I 2 C buffer  613  for output to electric cables T H19 -T D19  through T H20 -T D20 , and buffers the I 2 C communication data SDA received from the electric cable T H20 -T D20  by means of the I 2 C buffer  613  for output to the host device  11  or  21 . 
     The reception unit  62  operates when supplied with the power-supply voltage V CC  from the second power-supply switching unit  622 , converts the optical signals S R  through CLK of 4 channels received from the optical cables T H15 -T D15  through T H18 -T D18  into the digital image data S R+  through CLK− by means of a light reception amplification unit  621  for output to the display device  12  or  22 , buffers the I 2 C communication clock signal SCL and the I 2 C communication data SDA by means of the I 2 C buffer  613  for output to the display device  12  or  22 , and buffers the I 2 C communication data SDA received from the display device  12  or  22  by means of the I 2 C buffer  613  for output to the optical cable T H20 -T D20 . 
       FIG. 7  illustrates an optical cable module as a transmission/reception reinforcement device interposed between the host device  11  or  21  illustrated in  FIG. 1  or  2  and the display device  12  or  22  illustrated in  FIG. 1  or  2  according to a fourth embodiment of the present invention. In  FIGS. 3 and 7 , like reference numerals refer to like elements. In  FIG. 7 , internal circuits of a first power-supply switching unit  712  and a second power-supply switching unit  722  are the same as those illustrated in  FIG. 4 . Hereinafter, only a difference between the first embodiment illustrated in  FIG. 3  and the fourth embodiment illustrated in  FIG. 7  will be described in detail. 
     A repeater as the transmission/reception reinforcement device of the digital image system according to the fourth embodiment of the present invention includes a transmission unit  71  and a reception unit  72 . 
     The transmission unit  71  operates when supplied with a power-supply voltage V CC  from the first power-supply switching unit  712 , amplifies digital image data S R+  through CLK− of 8 channels, which have been received from the host device  11  or  21 , into optical signals S R  through CLK by means of a transition minimized differential signaling (TMDS) amplification unit  711  for output to optical cables T H15 -T D15  through T H18 -T D18 , and buffers an I 2 C communication clock signal SCL and I 2 C communication data SDA, which have been received from the host device  11  or  21 , by means of an I 2 C buffer  713  for output to electric cables T H19 -T D19  through T H20 -T D20 , and buffers the I 2 C communication data SDA received from the electric cable T H20 -T D20  by means of the I 2 C buffer  713  for output to the host device  11  or  21 . 
     The reception unit  72  operates when supplied with the power-supply voltage V CC  from the second power-supply switching unit  722 , restrictively amplifies the digital image data S R+  through CLK− received from the optical cables T H15 -T D15  through T H18 -T D18  by means of a TMDS restrictive amplification unit  721  for output to the display device  12  or  22 , buffers the I 2 C communication clock signal SCL and the I 2 C communication data SDA received from electric cables T H19 -T D19  and T H20 -T D20  by means of an I 2 C buffer  723  for output to the display device  12  or  22 , and buffers the I 2 C communication data SDA received from the display device  12  or  22  by means of the I 2 C buffer  623  for output to the electric cable T H20 -T D20 . 
       FIG. 8  illustrates an equalizer apparatus  82  as a transmission/reception reinforcement device interposed between the host device  11  or  21  illustrated in  FIG. 1  or  2  and the display device  12  or  22  illustrated in  FIG. 1  or  2  according to a fifth embodiment of the present invention. In  FIGS. 3 and 8 , like reference numerals refer to like elements. In  FIG. 8 , internal circuits of a first power-supply switching unit  812  and a second power-supply switching unit  822  are the same as those illustrated in  FIG. 4 . Hereinafter, only a difference between the first embodiment illustrated in  FIG. 3  and the fifth embodiment illustrated in  FIG. 8  will be described in detail. 
     An equalizer apparatus  82  as the transmission/reception reinforcement device of the digital image system according to the fifth embodiment of the present invention operates when supplied with the power-supply voltage V CC  from the second power-supply switching unit  823 , restores attenuated signals of digital image data S R+  through CLK− received from electric cables by means of a TMDS equalizer  821  for output to the display device  12  or  22 , buffers an I 2 C communication clock signal SCL and I 2 C communication data SDA received from electric cables by means of an I 2 C buffer  823  for output to the display device  12  or  22 , and buffers the I 2 C communication data SDA received from the display device  12  or  22  by means of the I 2 C buffer  823  for output to the electric cables.