Abstract:
There are provided systems and methods for cable detection, such as a video cable. There is provided a device including an output stage, a comparator, a reference selector, a peak detector, and logic gates, which may be arranged to optimize power consumption of the output stage while the cable is unplugged. A method is also provided for such a device, the method comprising detecting whether the cable is unplugged using a cable detector after a first duration of time, turning off the output stage for a second duration of time in response to the cable detector detecting the cable is unplugged, turning on the output stage after the second duration of time, and proceeding to transmit data if the cable detector detects the cable is plugged in for a third period of time, or otherwise repeating the detection, turning off, and turning on steps.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/211,882, filed Apr. 3, 2009, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is generally in the field of electrical circuits. More specifically, the present invention is in the field of cable detection circuits. 
         [0004]    2. Background Art 
         [0005]    Optimizing the power efficiency of electrical devices provides several advantages such as reduced operational costs and reduced thermal dissipation requirements. In particular, it is desirable to optimize power consumption when portions of the electrical device are idle or not in use. One such situation is where a cable driver output is connected to a port that has no cable connection to another device. For example, audio/visual equipment may include several output ports for the transmission of data, such as audio or video to other devices, but some of these output ports may not be connected. It is inefficient to power the cable driver output for these unused and disconnected ports. Thus, it is desirable to provide cable detection capabilities for the electrical device so that driver outputs for unused ports can be disabled for energy efficiency. 
         [0006]    Conventionally, cable connection status is detected by periodically sending a clock signal to the cable driver output. The cable driver output may be then disabled if the cable connection status is determined as disconnected. However, this approach generally requires an external component for generating the clock signal and a time delay to periodically wake-up the cable driver output. This undesirably increases the cost and complexity of the electrical device. 
         [0007]    Accordingly, there is a need in the art for providing cable detection in a simplified and cost efficient manner. 
       SUMMARY OF THE INVENTION 
       [0008]    There are provided systems and methods for cable detection, such as a video cable, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The features and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, wherein: 
           [0010]      FIG. 1  illustrates a diagram of a cable driver system having cable driver output stage and cable detector, according to one embodiment of the present invention; 
           [0011]      FIG. 2  illustrates a flowchart describing an operation of the cable driver system of  FIG. 1 , according to one embodiment of the present invention; and 
           [0012]      FIG. 3  illustrates a graph having peak detect curve and reference voltage curve for the cable driver system, according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Although the invention is described with respect to specific embodiments, the principles of the invention can obviously be applied beyond the specifically described embodiments of the invention described herein. Moreover, in the description of the present invention, certain details have been left out to not obscure the inventive aspects of the invention. The details left out are within the knowledge of a person of ordinary skill in the art. The drawings in the present application and their accompanying detailed description are directed to merely example embodiments of the invention. To maintain brevity, other embodiments of the invention which use the principles of the present invention are not specifically described in the present application and are not specifically illustrated by the present drawings. 
         [0014]      FIG. 1  shows a diagram of cable driver system  100  having cable driver output stage  102  and cable detector  103 , according to one embodiment of the present invention. Cable driver system  100  includes cable driver output stage  102  (hereinafter referred to simply as “output stage  102 ” in the patent application) having an input for receiving data to be transmitted on an output that can be coupled to an external cable, and cable detector  103 , which includes peak detector  104 , reference voltage selector  106 , comparator  108 , and logic gates  110 . In an embodiment of the present invention, cable detector  103  can be configured to detect when a cable, such as a video cable, is disconnected at the output of output stage  102  and to detect when the cable is reconnected at the output of output stage  102 . Cable detector  103  can be further configured to power down output stage  102  for a substantial amount of the time during which the cable is disconnected and to power up output stage  102  when the cable is reconnected. For example, cable detector  103  can reduce the power consumption of output stage  102  by approximately 95 percent when during the time when the cable is disconnected. 
         [0015]    With reference to  FIG. 1 , output of peak detector  104  is coupled to the positive (non-inverting) input of comparator  108 , and output of reference voltage selector  106  is coupled to the negative (inverting) input of comparator  108 . Comparator  108  switches to a logic high (i.e. a “1”) to detect that the cable has been disconnected. The time period of approximately 100 nanoseconds represents the time required for peak detector  104  to increase to a level greater than the reference voltage. In another embodiment, the time required for peak detector  104  to increase to a level greater than the reference voltage can be greater or less than approximately 100 nanoseconds. As shown in  FIG. 1 , input of peak detector  104  is coupled to a connector for the external cable, and input of reference voltage selector  106  is coupled to the output of comparator  108 . 
         [0016]    The output of comparator  108  is also coupled to logic gates  110 , which has outputs coupled to inputs of output stage  102  for forcing the output of output stage  102  to logic low or logic high, as described in conjunction with  FIG. 2  below. Logic gates  110  also includes an output indicating whether the cable has been disconnected or not. 
         [0017]    The operation of cable detector  103  and output stage  102  will be discussed in reference to flowchart  200  in  FIG. 2 . At step  202  of flowchart  200 , a cable, such as a video cable, is connected to the output of output stage  102  and data is being transmitted by output stage  102  in a normal operating mode. The maximum output voltage at the output of output stage  102  can be approximately 1.2 volts, for example. At step  204 , the cable has been disconnected from output stage  102  and data is still being transmitted by the output stage. The maximum output voltage at output stage  102  can be, for example, approximately 1.8 volts when the cable has been disconnected. 
         [0018]    At step  206 , after a time period of, for example, approximately 100 nanoseconds (ns), the output of peak detector  104 , which is coupled to the positive (non-inverting) input of comparator  108 , is greater than a reference voltage (i.e. a threshold voltage), which can be, for example, approximately 1.4 volts, and comparator  108  switches to a logic high (i.e. a “1”) to detect that the cable has been disconnected. The time period of approximately 100 nanoseconds represents the time required for peak detector  104  to increase to a level greater than the reference voltage. In another embodiment, the time required for peak detector  104  to increase to a level greater than the reference voltage can be greater or less than approximately 100 nanoseconds. 
         [0019]    The reference voltage can be provided by reference voltage selector  106 , which has an input coupled to the output of comparator  108  and an output coupled to the negative (inverting) input of comparator  108 . The reference voltage provided by reference voltage selector  106  can be lowered to, for example, approximately 1.3 volts to magnify hysteresis when detection of the disconnected cable has occurred. This increases the time until cable detector  103  checks to see if a cable has been connected to the output of output stage  102  by increasing the decay time of the peak detected voltage store in memory in peak detector  104 . A logic low is forced at the output of output stage  102  via logic gates  110 , which is coupled between the output of comparator  108  and output stage  102 , and output stage  102  is turned off, thereby reducing power consumption. 
         [0020]    At step  208 , since output stage  102  has been turned off at step  206 , the maximum output voltage at output stage  102  can be approximately 0.0 volts. Peak detector  104  senses the approximately 0.0 volt output of output stage  102  and the output of peak detector  104  slowly decays. The slow decay of the output of peak detector  104  occurs because the peak voltage that is stored in memory in peak detector  104  slowly decreases over time. 
         [0021]    At step  210 , after a predetermined time period has expired, which can be, for example, approximately 2.0 microseconds (μs), the output of peak detector  104  has decayed to a level that is less than the reference voltage of approximately 1.3 volts provided by reference voltage selector  106 . In another embodiment, the time period required for the output of peak detector  104  to decay below the reference voltage can be less than or greater than approximately 2.0 microseconds. As a result, the output of comparator  108  switches to a logic low (i.e. “0”) and reference voltage selector  106  provides a higher reference voltage of approximately 1.4 volts to the negative input of comparator  108 . At this point, data is not being transmitted by output stage  102 , which has been turned off during the predetermined time period of approximately 2.0 microseconds. A logic high is slowly forced at the output of output stage  102  by logic gates  110 , which receives the logic low output of comparator  108 , and output stage  102  is turned on. If the cable remains unplugged, output stage  102  will output a maximum voltage of, for example, approximately 1.8 volts, since there is no load on output stage  102 . If the cable is plugged into output stage  102 , output stage  102  will output a maximum voltage of, for example, approximately 1.2 volts. If the cable is not plugged into output stage  102 , flowchart  200  proceeds to step  212 ; and if the cable is plugged into output stage  102 , flowchart  200  proceeds to step  214 . 
         [0022]    At step  212 , if the cable is not plugged into output stage  102 , peak detector  104  receives a peak voltage of approximately 1.8 volts from output stage  102  and the output of peak detector  104  increases. The approximately 1.8 volts received from output stage  102  is interpreted as a cable off condition. Flowchart  200  proceeds back to step  206 . 
         [0023]    At step  214 , if the cable is plugged into output stage  102 , peak detector  104  receives a peak voltage of approximately 1.2 volts from output stage  102 . The approximately 1.2 volts received from output stage  102  is interpreted as a cable on condition. As a result of the approximately 1.2 volts received from output stage  102 , the output of peak detector  104  remains less than the reference voltage provided by reference voltage selector  106 . If the output of peak detector  104  remains less than the reference voltage provided by reference voltage selector  106  for a window time period of approximately 5.0 microseconds, the cable on condition is verified and flowchart  200  proceeds back to step  202 . If, during the window time period, the output of peak detector  104  increases above the reference voltage, a cable off condition is indicated and flowchart  200  proceeds to step  206 . In another embodiment, the window time period can be less than or greater than approximately 5.0 microseconds. 
         [0024]      FIG. 3  shows graph  300  according to one embodiment of the present invention. Graph  300  includes peak detect curve  302  and reference voltage curve  304 . As shown in graph  300 , peak detect curve  302  quickly rises to detect a peak voltage and slowly decays when the cable is unplugged from output stage  102  and there is no peak voltage to detect. Reference voltage curve  304  goes from approximately 1.4 volts when the cable is plugged into output stage  102  to approximately 1.3 volts when the cable is unplugged. 
         [0025]    Thus, in an embodiment of the present invention, when a cable is unplugged from output stage  102 , for a time period of approximately 100 nanoseconds, output stage  102  is turned on while cable detector  103  determines if the cable has been plugged in. If the cable has not been plugged in, output stage  102  is turned off for a time period of approximately 2.0 microseconds. After the time period of approximately 2.0 microseconds has expired, output stage  102  is turned on again for a time period of approximately 100 nanoseconds while cable detector  103  determines if the cable has been plugged in. The cycle discussed above can be repeated until the cable is plugged into output stage  102 . Thus, an embodiment of the present invention&#39;s cable detector  103  can substantially reduce the power consumption of output stage  102  by turning output stage  102  off for a substantial portion of the time during which the cable is unplugged from output stage  102 . For example, since according to one embodiment of the present invention, output stage  102  is only turned on about five percent of the time while the cable is disconnected, or 100 nanoseconds on for every 2 microseconds (2000 nanoseconds) off, a device integrating the described power stage can reduce power consumption by about 95% compared to a device with an always on power stage. By adjusting these time ratios within the limits imposed by peak detect curve  302  and reference voltage curve  304 , even greater savings in power consumption can be achieved. 
         [0026]    From the above description of the invention it is manifest that various techniques can be used for implementing the concepts of the present invention without departing from its scope. Moreover, while the invention has been described with specific reference to certain embodiments, a person of ordinary skills in the art would recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. As such, the described embodiments are to be considered in all respects as illustrative and not restrictive. It should also be understood that the invention is not limited to the particular embodiments described herein, but is capable of many rearrangements, modifications, and substitutions without departing from the scope of the invention.