Patent Publication Number: US-8109792-B2

Title: System with cable mode converter

Description:
FIELD OF THE INVENTION 
     The invention generally relates to cables for transmitting data and, more particularly, the invention relates to cables for transmitting component video within a computer system. 
     BACKGROUND OF THE INVENTION 
     Computers often use conventional coaxial cables to communicate with their associated display devices (e.g., cathode ray tube monitors, plasma displays, or liquid crystal display devices). For example, a desktop computer may transmit control and graphical data to a local liquid crystal display device across a conventional coaxial component video cable. These desktop computer systems often use coaxial cables because they transmit signals in a “single ended” format (also referred to as “single ended signals”), which, as known by those in the art, is 1) a standard mode that the transmitting computer transmits the control and graphical signals, and 2) a standard mode that the receiving display device is configured to process the received control and graphical signals. 
     Although useful, coaxial cables are expensive. Because their cost generally is a function of their length, however, a short coaxial cable may not be considered too expensive when compared to the cost of the overall computer system. For example, in the desktop environment, a $2000 system may have a three foot, $20 coaxial cable connecting its display device with its computer. 
     Using a conventional coaxial cable to transmit signals across relatively long distances, however, can be expensive. For example, a central server at an airport may transmit graphical data to a remote bank of display devices (also referred to in the art as “monitors”) listing flight arrival and departure times. The server could be on the order of up to 1000 feet from the display devices and thus, require a correspondingly long coaxial cable. The cost of appropriate coaxial cabling in such applications consequently can be on the order of, or greater than, the underlying hardware and software. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the invention, a cable has a drive interface, a receive interface with a differential-to-single ended converter, and a differential mode wired transmission medium connected to the drive interface and the receive interface. The differential-to-single ended converter is configured to convert differential mode signals into single ended signals. Stated another way, the differential-to-single ended converter converts one or more differential mode signals into one or more corresponding single ended signals. 
     In a manner corresponding to the receive interface, the drive interface may have a single differential-to-single converter configured to convert single ended signals into differential mode signals. In some embodiments, the drive interface and receive interface are substantially permanently secured to the transmission medium. Alternatively, the drive interface and receive interface are substantially removably secured to the transmission medium. In the latter case, the receive interface also has a port for directly connecting to a corresponding port of a logic device. 
     The cable may have a plurality of pins for coupling with a logic device (e.g., a computer or a display device). One or both of the drive interface and receive interface thus may have an additional port for receiving power. This additional port illustratively is uncouplable with the logic device. 
     Among other things, the transmission medium may have at least one twisted pair of wires. Moreover, one of the two interfaces may have cable compensation (i.e., delay skew compensation and equalization). 
     In accordance with another embodiment of the invention, a system has a display device, a logic device for forwarding data for generating a display on the display device, and a cable connected between the logic device and the display device. The cable is similar to that discussed above. Specifically, the cable has a drive interface directly connected to the logic device, a receive interface having a differential-to-single ended converter (and directly connected to the display device), and a differential mode data wired transmission medium connected to the drive interface and the receive interface. The differential-to-single ended converter is configured to convert differential mode signals into single ended signals. 
     The receive interface may have a first port for connecting directly with the display device, and a second port for removably connecting with the transmission medium. The differential-to-single ended converter may be configured to convert differential mode signals received from the second port into single ended signals to be forwarded to the first port. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Those skilled in the art should more fully appreciate advantages of various embodiments of the invention from the following “Description of Illustrative Embodiments,” discussed with reference to the drawings summarized immediately below. 
         FIG. 1  schematically shows a computer system that may implement illustrative embodiments of the invention. 
         FIG. 2A  schematically shows a cable implementing one embodiment of the invention. 
         FIG. 2B  schematically shows a cable implementing another embodiment of the invention. 
         FIG. 3  schematically shows various functional components within the cables shown in  FIGS. 2A and 2B . 
     
    
    
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     In illustrative embodiments, rather than having a single ended, coaxial wired transmission medium, a component video cable for connecting two single ended based logic elements has a differential mode wired transmission medium (e.g., a CAT-5 cable). To effectively implement this, the cable has built-in circuitry for converting differential mode signals into single ended signals. Additional embodiments also have built-in circuitry for converting single ended signals into differential mode signals. Details of illustrative embodiments are discussed below. 
       FIG. 1  schematically shows a computer system  10  that may implement illustrative embodiments of the invention. Among other things, the computer system  10  has a plurality of conventional logic devices, such as a computer  12 , one or more display devices  14  (e.g., cathode ray tube display devices, or a liquid crystal display devices), and various input devices (e.g., a mouse  16  and a keyboard  18 ). 
     The logic devices may be position in close proximity to each other, such as in a typical desktop computing arrangement, or spaced apart across large distances. Various examples of spaced apart systems include banks of display devices at airports listing flight arrival and departure times, movie theaters, retail stores, other buildings having a logic device that delivers graphical information to remote display devices, and even logic devices controlling operation of display devices outside of a building. 
     In accordance with illustrative embodiments of the invention, the computer system  10  has a specially configured cable  19  for transmitting component video data between the computer  12  and display device  14 . As known by those skilled in the art, component video is a type of analog video format that is transmitted or stored as three or more separate signals. For example, a component video signal may comprise separate red, blue, and green signals. Of course, other types of component video signals may be used. Discussion of one specific type of component video signal therefore is illustrative and not intended to limit various embodiments. 
     As is common in the art, the display device  14  in  FIG. 1  is configured to receive and process component video data received via a single ended signal only. In a corresponding manner, the computer  12  also is configured to transmit a single ended signal to the display device  14  across some connection device. In accordance with illustrative embodiments of the invention, the cable  19   
     1) receives, from the computer  12 , a single ended signal having graphical data, 
     2) converts this single ended signal into a differential mode signal, 
     3) transmits this differential mode signal across the majority of the cable  19 , and then 
     4) converts the differential mode signal back to a single ended signal for ultimate delivery to the display device  14 . 
     Because it has this functionality, the cable  19  can have a wired transmission medium  22  (see  FIGS. 2A-3 , discussed below) that transmits differential mode signals. For example, the wired transmission medium  22  can be similar to that in conventional CAT-5 cables (i.e., twisted wire pairs, discussed below). Accordingly, because differential mode wired transmission media generally are less expensive than coaxial cables, the display device  14  may be more cost effectively positioned very far from the computer  12 . For example, the display device  14  could be positioned 100-1000 feet from the computer  12 . 
       FIG. 2A  schematically shows additional details of one component video cable  19  implementing one embodiment of the invention. In a manner similar to other component video cables, the cable  19  in  FIG. 2A  has a drive interface  20 A for coupling the cable  19  with the computer  12 , a receive interface  20 B for coupling the cable  19  with the display device  14 , and a differential mode, wired transmission medium  22  connected directly to the two interfaces  20 A,  20 B. In illustrative embodiments, the wired transmission medium  22  has four twisted-pairs of wires (referred to herein as “twisted pairs  26 A- 26 D,” see  FIG. 3 , discussed below) extending between the interfaces  20 A,  20 B, and a flexible outer insulator acting as a conduit for containing the twisted-pairs  26 A- 26 D. For example, as noted above, the wired transmission medium  22  could be similar to those used by conventional CAT-5 cables. 
     Each of the interfaces  20 A,  20 B therefore has one or more pins  24  corresponding to the wires of the twisted pairs  26 A- 26 D. The interfaces  20 A,  20 B thus may be similar to other devices conventional used for these purposes, also known as “connectors.” Continuing with the example above, three of the four twisted pars  26 A,  26 B,  26 C respectively may be used to transmit red, green, and blue signals, along with certain horizontal and vertical synchronization information. The fourth pair  26 D may be used for other purposes, such as for transmitting audio, control, or other data between the display device  14  and computer  12 . 
     As discussed in greater detail below with regard to  FIG. 3 , circuitry is intergrated directly into the cable  19  to convert signals between a single ended format and a differential mode. This circuitry, which illustratively is located in the interfaces  20 A,  20 B, must have a power source. In the example above, the fourth twisted par  26 D may transmit power to the circuitry from the computer  12 , the display device  14 , or both the computer  12  and the display device  14 . Another embodiment may use batteries. 
     In illustrative embodiments, the receive interface  20 B has a power port  28  (not directly connectable to either of the logic devices) for receiving a DC power signal from a conventional external adapter  30  that converts AC wall voltage to a suitable DC voltage. To that end, the adapter  30  includes a pair of prongs  32  to mate with a standard wall plug (e.g., a home AC outlet, such as those in North America and Europe), and internal transformation and rectification circuitry (not shown) for producing a DC power signal. The DC voltage is applied to the receive interface  20 B via an electrical cord  34  that plugs into the power port  28 , thus energizing circuitry in both interfaces  20 A,  20 B. In this case, one or more of the wires within the wired transmission medium  22  (e.g., the fourth twisted pair  26 D of the above noted example) transmits the power to the circuitry within the drive interface  20 A. 
     Alternatively, the drive interface  20 A could have the power port  28  and thus, transmit power to the circuitry within the receive interface  20 B. As another example, both interfaces  20 A,  20 B have a power port  29  and/or their own source of power. Discussion of the exact location of the power port  28  therefore is illustrative not intended to limit various aspects of the invention. 
     The wired transmission medium  22  shown in  FIG. 2A  is considered to be substantially permanently connected/integral to both of its interfaces  20 A,  20 B. In other words, during normal use, the wired transmission medium  22  is not readily detachable from either of the interfaces  20 A,  20 B. In addition if detached, such medium  22  is not readily re-attachable to the interfaces  20 A,  20 B. It can be envisioned, however, that some could forcibly separate the medium  22  from the interfaces  20 A,  20 B. For example, one could cut the wired transmission medium  22  from one of the interfaces  20 A,  20 B, or pull apart the medium  22  and one of the interfaces  20 A,  20 B. If forcible action similar to those discussed is required, for example, then the medium  22  is considered to be permanently connected to the interfaces  20 A,  20 B. 
     In contrast, the wired transmission medium  22  may be removably connected to one or both of the interfaces  20 A,  20 B.  FIG. 2B  schematically shows one such embodiment, where each end of the transmission medium  22  has a clip  36 A for removably clipping to a corresponding clip port  36 B on the interfaces  20 A,  20 B. Among other things, such clips  36 A may be similar to those used in a conventional Ethernet cables or telephone cables. 
     The cable  19  of  FIG. 2B  provides number of advantages. Among others, it can be more readily passed along narrow wiring conduits because it does not have the enlarged interfaces  20 A,  20 B one or both of its ends. In addition, in the event that circuitry in one of the interfaces  20 A,  20 B malfunctions, only a new interface  20 A,  20 B must be provided, thus not requiring an entirely new cable  19 . 
     In yet other embodiments, one end of the transmission medium  22  is removably connected to one interface  20 A,  20 B, while the other end is substantially permanently connected to the other interface  20 A,  20 B. To implement such an embodiment, one end of the transmission medium  22  may have a clip  36 A, and one interface  20 A,  20 B may have a corresponding clip port  36 B. 
       FIG. 3  schematically shows a generalized electrical diagram of various internal components of the computer  12 , cable  19 , and display device  14 . To that end,  FIG. 3  shows additional details of the conversion circuitry within each of the interfaces  20 A,  20 B, as well as other circuitry that may be within the receive interface  20 B. As a preliminary matter, it should be noted that although the drawings schematically shows three signal chains, various embodiments may have more or fewer signal chains. Discussion of three chains thus is for illustrative purposes only. 
     As shown in  FIG. 3 , the drive interface  20 A has three single ended-to-differential converters  39  for converting single ended signals (received from the computer  12 ) into differential mode signals to be transmitted across the wired transmission medium  22 . In the example shown, one single ended-to-differential converter  38  converts signals with red information, another single ended-to-differential converter  38  converts signals with green information, and a third single ended-to-differential converter  38  converts signals with blue information. In addition, the single ended-to-differential converters  38  also convert horizontal synchronization data and vertical synchronization data. 
     The single ended-to-differential converters  38  can be any of a wide number of conventionally known converters adapted for this application. For example, among others, one or more of the single ended-to-differential converters  38  may be the AD8134 Triple Differential Driver with Sync-On-Common Mode, distributed by Analog Devices, Inc. of Norwood, Mass. 
     The receive interface  20 B has a corresponding set of differential-to-single ended converters  40  that each convert differential mode signals received from the medium  22  into single ended signals. Continuing with the example in  FIG. 3 , the receive interface  20 B has a first differential-to-single ended converter  40  for converting signals with red information, another differential-to-single ended converter  40  for converting signals with green information, and a third differential-to-single ended converter  40  for converting signals with blue information. By way of example, among others, one or more of the differential-to-single ended converters  40  may be the AD8143 High Speed, Triple Differential Receiver with Comparators, distributed by Analog Devices, Inc. 
     The resulting single ended signals optionally may be transmitted directly to corresponding buffers  42 , and then to the display device  14 . Some embodiments of the receive interface  20 B, however, have additional circuitry for improving the quality of the signal transmitted to the display device  14 . Specifically, the receive interface  20 B also may have cable compensation that compensates for delay skew and provides equalization functionality. More specifically, as known by those skilled in the art, the wires within the transmission medium  22  may not be exactly the same length. This may be the result of the wire pairs  26 A- 26 D within the medium  22  having different twist rates. If the wires are not the same length, the resultant signals can be skewed. In addition, if the cable lone enough, the signals may experience some high frequency loss and thus, require equalization. 
     Accordingly, to compensate for these potential problems, the receive interface  20 B has one equalizer  44  coupled to each differential-to-single ended converter  40 , and one skew module  46  coupled to each equalizer  44 . The equalizers  44  and skew modules  46  may be those conventionally used for these purposes. For example, the AD8128 equalizer, also distributed by Analog Devices, Inc. may be used, while any appropriate conventional analog time delay skew compensator may be used. 
       FIG. 3  shows the three sets of differential-to-single ended converters  40 , equalizers  44 , skew modules  46 , and buffers  42  as separate components within the receive interface  20 B. In some embodiments, however, all of those components are integrated into a single die. In other embodiments, these separate components can be implemented as two or more die having the functionality of one or more of the noted circuit blocks. 
     Accordingly, during operation, the computer  12  shown in  FIG. 3  generates a single ended component video signal for transmission across the cable  19 . The single ended-to-differential converters  38  in the drive interface  20 A convert this single ended signal to a differential mode signal for transmission across the wired transmission medium  22 . Corresponding differential-to-single ended converters  40  in the receive interface  20 B convert these signals back to single ended signals, which, optionally, then are equalized and skew compensated before transmission to the display device  14 . The display device  14  then processes the data received in the single ended signal to ultimately produce a visual display. 
     Although the above discussion discloses various exemplary embodiments of the invention, it should be apparent that those skilled in the art can make various modifications that will achieve some of the advantages of the invention without departing from the true scope of the invention.