Patent Document

This application is a continuation of U.S. patent application Ser. No. 09/540,150 filed on Mar. 31, 2000 now U.S. Pat. No. 6,731,347, which claims the benefit of U.S. Provisional Application No. 60/128,536 filed Apr. 9, 1999. 

   BACKGROUND 
   1. Field of the Invention 
   The present invention is related to the field of signal transmission. More specifically, the present invention is a method and apparatus for switching input terminals based on a device&#39;s capability. 
   2. Related Art 
   Use of digital interfaces is a trend in signal transmission, as a result of recent developments in digital signal processing technologies. Analog video and audio signals are digitized and coded, or compressed, before being transmitted. Various types of compression techniques, including DVI (Digital Video Interactive) and MPEG (Motion Picture Experts Group) compression, have been developed to achieve high-performance digital signal transmission. Standards developed for digital interfaces, such as IEEE1394, allow digital signals in various formats to be transmitted through a single digital interface. Such standards, however, do not regulate the formats in which the signal is coded, nor control the transmission path through which the signal is transmitted. 
   It is vital to ensure that a device that receives a digital signal in a particular format is capable of decoding it to recover an original signal from it. This requirement was relatively easy to satisfy when digital signals were coded and transmitted in a limited number of formats such as the DV (Digital Video) format. Development of digital signal processing technologies has led to different formats, and distinctive modes exist for some formats with regard to the transmission speed and bandwidth of the signal. Devices that receive and use transmitted signals are not necessarily provided with decoders corresponding to the various formats, due to economic reasons. One problem that has emerged is that an incoming signal is not always received in a usable format, and if this is the case, a device using the signal cannot decode the transmitted digital signal. A digital TV that can process digital signals exclusively in the format based on the MPEG Standard, for example, cannot process signals coded in the DV format or the DSS (Digital Satellite System) format. 
   In addition to the differences between the coding formats of digital signals, signals are not always transmitted in a digital format but also in an analog format, particularly in a transition period from analog to digital, while both formats are in use. In other words, analog signals can co-exist with digital signals. 
   Some transmitters and receivers, having both analog and digital interfaces, are designed to process digital signals as well as analog. In order to transmit an analog signal to such a device, the signal has to be transmitted through the analog interface. Otherwise the signal cannot be transmitted to the receiver. It is vital, therefore, to select an appropriate transmission path, i.e., the digital interface or the analog interface, depending upon the type of the signal, digital or analog. 
   For the foregoing reasons, there is a need for a method for switching input terminals based on a device&#39;s capability. 
   SUMMARY 
   The present invention is directed to a method and apparatus that satisfies the need for switching between input terminals based on a transmitted signal format. 
   Whether or not a device is receiving a digital signal at a digital input terminal in a usable format is examined; and an analog input terminal is selected to receive an analog signal unless the digital signal is being provided in the usable format. 
   More specifically, the method includes receiving a digital signal at a digital input terminal of a device, receiving an analog signal at an analog input terminal of the device, examining whether or not the digital signal is in a usable format for the device, and selecting the digital signal if the digital signal is in the usable format, otherwise selecting the analog signal, as an input for the device. The digital signal and the analog signal may be supplied to the device simultaneously. 
   An apparatus to which the present invention is directed includes a digital input terminal which receives a digital signal, an analog input terminal which receives an analog signal an IEEE1394 interface coupled with the digital input terminal, a decoder coupled with the IEEE1394 interface, a memory and a selector which selects the digital input terminal if the digital signal is in a usable format for the apparatus, otherwise it selects the analog input terminal. The selector may include a controller for examining whether or not the decoder is capable of decoding the digital signal, and a switch controlled by the controller so as to select the digital input terminal if the decoder is capable of decoding the digital signal, otherwise to select the analog input terminal. 
   According to the present invention, it is possible to supply a usable signal in an analog form even though a digital signal is received in a format that the device cannot decode. Therefore, a user of digital equipment does not have to manually change the input terminal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an exemplary signal transmitting system comprising a satellite broadcasting receiver (DSS-IRD) and a digital television (DTV). 
       FIG. 2  illustrates an exemplary arrangement of a DSS-IRD in a block diagram. 
       FIG. 3  illustrates an exemplary arrangement of a DTV in a block diagram. 
       FIG. 4  illustrates operations of a DSS-IRD and a DTV, and the signal flows between them, in steps. 
       FIG. 5  illustrates a capability table for a DSS-IRD. 
       FIG. 6  illustrates a capability table for a DTV. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the figures, exemplary embodiments of the invention will now be described. The exemplary embodiments are provided to illustrate the invention and should not be construed as limiting the scope of the invention. 
   Consider a case where a digital television (DTV) receives an audio/video signal via a digital satellite-broadcasting receiver. 
     FIG. 1  illustrates an exemplary arrangement of a signal transmitting system which includes two electronic devices, i.e., a DSS-IRD (Digital Satellite System Integrated Receiver Decoder)  11  and a digital TV (DTV)  12 . In this embodiment of the present invention, these devices are connected to each other by an IEEE1394 digital interface cable  14  as well as an analog video/audio cable  16 . 
   The digital interface cable  14  is based upon the IEEE1394 Standard for a high-performance serial bus, and provides a peer-to-peer interface between various digital peripherals with up to 63 isochronous digital communication channels. The IEEE1394 digital interface  14  is capable of carrying digital video/audio signals in various digital formats, such as the DVI format and MPEG1/2 formats. Assuming that both the DSS-IRD  11  and the DTV  12  are also based upon the IEEE1394 Standard, the digital interface cable  14  allows a digital video/audio signal from the DSS-IRD  11  to be transmitted to the DTV  12 . In addition to the digital interface  14 , the analog audio/video cable  16  is provided between the DSS-IRD  11  and the DTV  12 , because both a digital signal and an analog signal can be provided from the DSS-IRD  11 . 
   The DSS-IRD  11  is a satellite broadcasting receiver based upon the DSS Standard, which is one of the standards for satellite broadcasting in the United States. According to the DSS Standard, an audio/video signal is digitized and coded in the MPEG2 format, which is one of the global standards for video compression. The coded signal including program-related information is transmitted in two original modes of the DSS Standard, i.e., SD (Standard Definition) and HD (High Definition). 
   The SD mode is designed for transmitting an MPEG2 signal in a standard quality, whereas the HD mode is for high-quality transmission. Since the SD mode is the DSS&#39;s unique mode, a DSS-SD decoder is required to decode a signal transmitted in this mode. The HD mode is, on the other hand, partly based upon the ATSC (Advanced Television Systems Committee) system, which is used for surface digital broadcasting in the United States. To decode a signal transmitted in the HD mode, an ATSC decoder may be used. 
   Under such a circumstance, the DSS-IRD  11  will not need to have an expensive DSS-HD decoder, if the DTV  12  with a built-in ATSC decoder is provided with a decoding function for DSS-HD signals. In this case, signals can be transmitted to the DTV  12  in different formats. Namely, a DSS-SD signal received at the DSS-IRD  11  is decoded into an analog signal in the DSS-IRD  11 , and then the analog signal is transmitted to the DTV  12  via the analog video/audio cable  16 . A DSS-HD signal is, meanwhile, received at the DDS-IRD  11  and is transmitted through the digital interface cable  14  to the DTV  12 . The digital signal is then decoded in the DTV  12  into an analog signal. 
     FIGS. 2 and 3  illustrate exemplary arrangements of the DSS-IRD  11  and the DTV  12 , respectively. 
   As shown in  FIG. 2 , the DSS-IRD  11  includes a DSS-SD/HD receiver  114 , a DSS-SD decoder  116 , a digital input/output terminal  110 , and an analog output terminal  112 , and an IEEE1394 interface  121 , and a memory  151 . It is noted that the DSS-IRD  11  does not have a DSS-HD decoder but only the DSS-SD decoder  116 . The memory in the present embodiment is provided in configuration ROM (Read Only Memory). However, one skilled in the art will recognize that other storage devices may be used. 
   The receiver  114 , connected to an antenna  118 , is capable of receiving both DSS-SD and DSS-HD signals from a satellite. These digital signals received at the receiver  114  will be supplied to the digital input/output terminal  110 . In addition, the receiver  114  also provides the digital signals to the DSS-SD decoder  116 , which decodes the DSS-SD signal into an analog audio/video signal. When a DSS-SD signal is being received, therefore, the DSS-SD decoder  116  will supply to the analog output terminal  112  an analog audio/video signal, which is derived from the digital signal. 
   As shown in  FIG. 3 , the DTV  12  has a digital input/output terminal  120 , an analog input terminal  122 , an HD decoder  124 , a monitor  126  including a display and speakers, an IEEE1394 interface  141 , a switch  128  for selecting an input terminal, and a selector  130  including a controller  140  to control the switch  128 , and a memory  160 . The memory in the present embodiment is provided in configuration ROM (Read Only Memory). However, one skilled in the art will recognize that other storage devices may be used. As illustrated in  FIG. 1 , the digital input/output terminal  120  communicates with the digital input/output terminal  100  of the DSS-IRD  11  via the digital interface cable  14 , so that it receives both DSS-SD and DSS-HD signals from the DSS-IRD  11 . The analog input terminal  122  is connected to the analog output terminal  102  by the analog video/audio cable  16 , so that an analog audio/video signal can be received. 
   Within the DTV  12 , the HD decoder  124  decodes an incoming DSS-HD signal transmitted through the digital interface cable  14  that arrives at the digital input terminal  120  and passes through the IEEE1394 interface  141 . When an HD signal is transmitted from the DDS-IRD  11 , the HD decoder  124  will decode the digital signal into a corresponding analog audio/video signal, which will be generated on the monitor  126 , and supply it to a first terminal “a” of the switch  128 . 
   An analog audio/video signal is also obtained at the analog input terminal  122 , when a DSS-SD signal is being received at the DSS-IRD  11 . The analog audio/video signal, which is decoded by the DSS-SD decoder  116  of the DSS-IRD  11 , is provided to a second terminal “b” of the switch  128 . Accordingly, an analog audio/video signal will be supplied from either the terminal “a” or “b” to the monitor  126  via a third terminal “c” of the switch  128 . 
   The controller  140  controls the switch  128  based upon the DTV&#39;s capability of decoding an incoming digital signal. More specifically, the controller  140  monitors the output of the HD decoder  124 , and will control the switch  128  to select its first terminal “a” if the HD Decoder  124  provides an analog audio/video signal, otherwise will direct the switch  128  to select its second terminal “b.” 
   Each device can have a capability list. The capability list may be stored in a device&#39;s memory. The memory in the present embodiment is provided in configuration ROM (Read Only Memory). However, one skilled in the art will recognize that other storage devices may be used to store a capability list. Since configuration ROM typically does not have much room to store information, e.g. 1024 bytes, keywords or brief information may be stored. Therefore, to store detailed information, additional memory units can be used. 
   Such capability information may be stored using a descriptor based upon the IEEE1394 Standard p1212r 64-bit fixed addressing. A descriptor is a leaf (a contiguous information field pointed to by a configuration ROM directory entry) that provides additional information to describe an object associated with a directory entry in configuration ROM. 
   Devices may inquire into the capabilities of other devices by issuing a command on the IEEE1394 digital interface  14  to receive capability information. The queried device then responds to the inquiry command and will send the information to the device that issued the query command on the IEEE1394 digital interface  14 . Two examples of a capability list are illustrated in  FIGS. 5 and 6 , for IRD and DTV capabilities, respectively. 
   In the case of DTV, since each device has a capability list, DTV can select compatible devices according to the information in their capability list. Once the device is selected, the DTV establishes an isochronous connection. Depending upon the selected device&#39;s status, the selected device may output a signal onto the IEEE1394 digital interface  14  where the DTV picks up the signal. The output signal from the selected device has a field to indicate the signal format type. The format type, which may be changed dynamically, depends on the contents or situation of the device. For example, a Digital VHS can play MPEG2, DSS and analog. The DTV keeps monitoring the signal format field to determine whether to process the signal or not. This is a second stage of determination. For instance, if the signal is MPEG2, a selector  130  enables HD decoder  124  and selects switch “a” to feed the signal to a monitor  126 . If the signal is analog, the selector  130  selects switch “b.” If the signal is such that it is not compatible for this particular DTV, DV for example, then selector  130  may disable HD decoder  124 . 
   Operation 
   The operation of the DTV  12  will be described with reference to  FIG. 4 . 
     FIG. 4  illustrates an operation of the transmission system step by step. In  FIG. 4 , the column “Situation” shows a format of the signal transmitted from the DSS-IRD  11 . The column “Action by User” indicates the action that a user of the system is taking. Let us assume that the user is watching a satellite TV program received at the DSS-IRD  11  on the DTV  12 . 
   The column “Signal flow” in  FIG. 4  shows a signal flow from the DSS-IRD  11  to the DTV  12  and the channel through which the signal is being transmitted. Based on the IEEE1394 Standard, the digital interface cable  14  provides up to 63 isochronous digital communication channels, and allows more than two devices to communicate with each other. These channels are denoted by “CH63,” “CH X” and “CH Y” in  FIG. 4 . Video/Audio cable  16  provides a communication channel for an analog signal. For the case of a digital signal, the channel is assigned dynamically. For the case of an analog signal, unlike the digital signal, once it is connected, there is no dynamic assignment. 
   The columns “IRD” and “DTV” indicate the operations or workings of the IRD  11  and the DTV  12 , respectively. 
   Assume that the DSS-IRD  11  has been selected by the user to supply an input signal to the DTV  12 . The DSS-IRD  11  is receiving a DSS-HD signal at this stage. An isochronous communication, called “point-to-point” connection, has been established between the DSS-IRD  11  and the DTV  12 . Receiving a DSS-HD signal, the DSS-IRD  11  is transmitting to the DTV  12  the digital signal in the MPEG2-HD format through one of the digital communication channels, “CH X,” as illustrated by an arrow. 
   Within the DTV  12  (refer to  FIG. 3 ), the incoming digital signal is input to the HD decoder  124  to be decoded into the analog video/audio signal, which the monitor  126  can cope with. The analog output of the HD decoder  124  is then being supplied to the terminal “a” of the switch  128 . Since the incoming digital signal is in the HD format, which the DTV  12  is capable of decoding, the switch  128  is making a connection between its terminals “a” and “c.” Accordingly, the video/audio signal decoded by the HD decoder  124  is being supplied to the monitor  126 . 
   The format that the DSS-IRD  11  receives has changed, and the DSS-IRD is now receiving a DSS-SD signal. The DSS-IRD  11  decodes the digital signal in the MPEG2-SD format to an analog signal using its SD-decoder  116 , and the analog signal is provided to its analog output terminal  112 , so that it is transmitted to the DTV  12  through the analog audio/video cable  16 . At the same time, the digital signal in the MPEG2-SD format is provided to the digital input/output terminal  110  and transmitted to the DTV  12  via the digital interface cable  14 . 
   The DTV  12  receives the digital signal in the MPEG2-SD format and the analog signal at the digital input/output terminal  120  and the analog input terminal  122 , respectively. 
   Since the DTV  12  only has a HD decoder  124 , the digital signal is in an ineligible format. Within the DTV  12 , therefore, the HD decoder  124  can no longer provide a usable signal for the monitor  126 . Nevertheless, the DTV  12  examines the format of the incoming digital signal and, as it recognizes that it is receiving a digital signal, switches to the analog input terminal  122  from its digital input/output terminal  120 . 
   More specifically, the controller  140  controls the switch  128  based upon the DTV&#39;s capability of decoding an incoming digital signal. The controller  140  sends a command to the switch  128  to select the second terminal “b.” As a result, the analog signal, which is being decoded in the DSS-IRD  11  and provided to the analog input terminal  122 , is directed to the monitor  126  through the connection between the terminals “b” and “c.” 
   Accordingly, the video/audio signal will be provided to monitor  126  in an eligible format even after the format of the transmitted signal has changed. Therefore, the user of the system does not have to manually select the input terminal. 
   Moreover, in the preferred embodiment of the present invention, the digital signal is provided to the digital input/output terminal  120  of the DTV  12 , after the switch  128  makes a connection between terminals “b” and “c.” In other words, the format of the digital signal will be examined while the analog signal received at the analog input terminal  122  is being directed to the monitor  126 . The input terminal of the DTV  12  will, therefore, be switched back to its digital input/output terminal  120  when the digital signal in the DSS-HD format is transmitted again. The operation explained above will be particularly effective where the format of the transmitted signal changes between digital and analog. 
   The present invention is applicable in circumstances where:
         a digital signal and an analog signal that have been recorded on a single medium are played back in a digital VHS (DVHS) system   a DV signal is provided to a digital TV that is incapable of decoding the DV format.       

   The present invention can also allow digital equipment to be used even if a digital signal is provided in a format that is unknown when the device is designed. 
   The embodiments of the invention described above are, of course, subject to other variations in structure and implementation. For instance, additional devices may be inserted between various nodes, terminals, and devices in the above embodiments without materially changing their overall function. In general, the scope of the invention should be determined not by the embodiments illustrated but by the appended claims and their legal equivalents.

Technology Category: h