Patent Document

CROSS REFERENCE TO RELATED PATENT APPLICATION 
     This patent application is based on Taiwan, R.O.C. patent application No. 099116096 filed on May 20, 2010. 
     FIELD OF THE INVENTION 
     The present invention relates to a data transmission interface and an electronic device thereof, and more particularly, to the data transmission interface that distinguishes a type of a data transmission interface via which the electronic device is connected to an electronic apparatus, and the electronic apparatus using the data transmission interface. 
     BACKGROUND OF THE INVENTION 
     Presently, mobile phones or portable electronic devices such as PDAs, navigators, etc., are usually connected to chargers or PC devices via USB interfaces.  FIG. 1  is a schematic diagram of a circuit structure of an electronic device utilizing the USB interface of the prior art. As shown in  FIG. 1 , the electronic device  100  communicates and connects to a charger  109  via a USB interface  102 . The USB interface  102  usually comprises four lines: a power line  101  (V Bus ), a ground line  103 , a DP signal transmission line  105 , and a DN signal transmission line  107 . The power line  101  and the ground line  103  are used for supplying power to electronic devices when the electronic devices are coupled to the charger  109  via the USB interface  102 . Detailed operations of the USB interface are well-known to those skilled in the art and are therefore omitted herein. 
       FIG. 2  is a schematic diagram of an electronic device coupled to a PC device or a charger. As shown in  FIG. 2 , the electronic device  100 , a mobile phone in the example, may be coupled to a PC device  205  or the charger  109  via the USB interface  102 . The two ends of the USB interface  102  may be plugs of different specifications, for example, one end is USB plug  209  (Mini A USB) while the other end is USB plug  211  (Type A USB), or plugs of the same specification, i.e. both are Mini A USB or both are Type A USB. The USB plug  209  is utilized for connecting to the electronic device  100 , while the USB plug  211  is utilized for connecting to the PC device  205  or the charger  109 , thus, a mechanism is needed for distinguishing whether the electronic device  100  is coupled to the PC device  205  or the charger  109 . With reference again to  FIG. 1 , and taking a conventional charger as an example, a detection circuit  111  is usually added to the charger  109  for assisting the electronic device  100  using the USB interface  102  to distinguish whether the electronic device  100  is coupled to a PC device or to a charger. That is to say, additional designs for circuits are needed, which results in not only increase of costs, but also inconvenience for users, because electronic devices produced by different companies can not share the same detection circuit in the charger. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary objective of the claimed invention to provide a data transmission interface and an electronic device using the same, capable of distinguishing the electronic apparatus coupled to the electronic device. 
     An embodiment of the present invention provides a data transmission interface, for coupling to an external apparatus, comprising a first signal transmission line and a second signal transmission line, for transmitting a differential signal, a first resistor and a voltage-variable component, alternatively connected to the first signal transmission line, and a second resistor, connected to the second signal transmission line, wherein, when the data transmission interface is coupled to an external apparatus, the voltage-variable component is connected to the first signal transmission line, and the first signal transmission line presents a first voltage according to the external apparatus, accordingly. 
     Another embodiment of the present invention provides an electronic device comprising a signal line pair, comprising two signal lines, for transmitting a differential signal, a pair of boost resistors, respectively connected to one of the corresponding signal line of the signal line pair while transmitting the differential signal, and a voltage-variable component, alternatively connected to one of the signal line of the signal line pair, for distinguishing the type of the apparatus while the electronic device is coupled to an external apparatus initially. Wherein, when the electronic device is coupled to the external apparatus, the voltage-variable component is connected to the signal line connected to the voltage-variable component, which presents a first voltage in response to the external apparatus. 
     Another embodiment of the present invention provides a method for data transmission, comprising transmitting a differential signal via a data transmission interface, comprising a first signal transmission line and a second signal transmission line, connecting a voltage-variable component to the first signal transmission line while the data transmission interface is coupled to an external apparatus, wherein the first signal transmission line presents a corresponding voltage in response to a type of the apparatus, and connecting the first signal transmission line to a first resistor and disconnecting the first signal transmission line from the voltage-variable component, after the corresponding voltage is presented in the first signal transmission line. 
     According to the embodiments described above, the present invention is capable of distinguishing a type of the electronic apparatus coupled to the electronic device without any external circuit in the charger and, furthermore, the present invention can switch the signal transmission line of the electronic device after the type of the apparatus is confirmed, enabling the electronic device to operate in a normal state. 
     The advantages and spirit related to the present invention can be further understood via the following detailed description and drawings. 
     Following description and figures are disclosed to gain a better understanding of the advantages of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a circuit structure of an electronic device utilizing the USB interface of the prior art. 
         FIG. 2  is a schematic diagram of an electronic device coupled to a PC device or a charger. 
         FIG. 3  is a schematic diagram of a USB interface according to a preferred embodiment of the present invention. 
         FIG. 4  is a flowchart of a USB interface according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 3  is a schematic diagram of a USB interface according to an embodiment of the present invention. As shown in  FIG. 3 , an electronic device  300  is connected to a PC device  315  via a USB interface  302 . The USB interface  302  usually includes four lines: a power line  301 , a ground line  303 , a DP signal transmission line  305 , and a DN signal transmission line  307 . Two boost resistors  309  and  311  (1.5 k Ohm in the example) are respectively disposed on the DP signal transmission line  305  and the DN signal transmission line  307 . According to the specification of the USB, when the DP signal transmission line  305  is connected to the boost resistor  309 , causing the voltage of the DP signal transmission line  305  to be pulled up, and the DN signal transmission line  307  is disconnected from the boost resistor  311  (which may be controlled by a switch, which is not depicted herein), the USB interface  302  operates in high speed. When the DN signal transmission line  307  is connected to the boost resistor  311 , causing the voltage of the DN signal transmission line  307  to be pulled up, and the DP signal transmission line  305  is disconnected from the boost resistor  309 , the USB interface  302  operates in low speed. In addition, a voltage-variable component  313  is set on either the DP signal transmission line  305  or the DN signal transmission line  307  (in the embodiment, the voltage-variable component  313  is a 1M Ohm resistor disposed on the DP signal transmission line  305 , but the present invention is not limited thereto). 
     When the electronic device  300  is not yet connected to any devices (chargers or PC devices) via the USB interface  302 , the voltage of the DP signal transmission line  305  is at a high level (i.e., a logic voltage level equals 1). When the electronic device  300  is coupled to the computer device  315 , the DP signal transmission line  305  and the DN signal transmission line  307  are respectively coupled to the resistor  317  and  319  (both 15 k Ohm resistors in the embodiment) of the PC device  315 , and are further connected to the ground, such that the voltage of the DP signal transmission line  305  may be pulled down from the high level to a low level (i.e. the logic voltage level equals 0); whereas, as regards a charger, the inner circuit of the charger connected to the USB interface  302  has no additional resistors designed for pulling down the voltage level of the DP signal transmission line  305  or the DN signal transmission line  307  to the low level, so the DP signal transmission line  305  maintains at the high level voltage when the electronic device  300  is coupled to the charger. Therefore, whether the electronic device  300  is coupled to the computer device  315  or to the charger can be determined according to change of the logic voltage level of the DP signal transmission line  305  or the DN signal transmission line  307 . That is, when the electronic device  300  is coupled to a device, if the logic voltage level of the DP signal transmission line  305  changes from 1 to 0, it indicates that the device is a computer device; and if the DP signal transmission line  305  maintains at the high level voltage, then it indicates that the apparatus is a charger. 
     In another embodiment of the present invention, the USB interface  302  further includes a switch component  321  (controlled by, e.g., a register), for alternatively connecting the DP signal transmission line  305  to the voltage-variable component  313  or the boost resistor  309 . The voltage-variable component  313  may be treated as a voltage boosting component of a resistance different from the resistance of the boost resistor  309 . In an initial state, the DP signal transmission line  305  is connected to the voltage-variable component  313  via the switch component  321 , and further connects to a voltage source V DD . After the electronic device  300  is coupled to the PC device  315 , the switch component  321  switches to connect the boost resistor  309 , resulting in the DP signal transmission line  305  connected to the voltage source V DD  via the boost resistor  309 ; meanwhile, if the DN signal transmission line  307  is not connected to the boost resistor  311 , the USB interface  302  operates in a high speed state. Please note that all of the resistances of the resistors are merely examples, and the present invention is not limited thereto. When the voltage-variable component  313  is a resistor, it is feasible as long as the resistance thereof is capable of resulting in a variation of the logic voltage level of the DP signal transmission line  305  or the DN signal transmission line  307  while the present invention is coupled to the PC device via the USB interface  302 . The resistances of the boost resistors  309  and  311  and the resistors  317  and  319  in the PC device vary with different specifications. The operations of the voltage-variable component  313  while disposed on the DN signal transmission line  307  is identical to those on the DP signal transmission line  305 , and are therefore omitted herein. When the voltage-variable component  313  is disposed on the DN signal transmission line  307 , a switch is adopted for controlling whether the DN signal transmission line  307  is connected to the boost resistor  311 . If the DN signal transmission line  307  is connected to the voltage source V DD  via the boost resistor  311 , while the DP signal transmission line  305  is not connected to the boost resistor  309 , the USB interface  302  operates in low speed. 
     Please note that the present invention is not limited to distinguishing between the computer device and the charger for which is coupled to the electronic device, in that it can also adopt to which of other electronic devices with different loads is coupled to by utilizing variation of the voltage. Moreover, the present invention is not limited to the USB interface; it can also be used in other data transmission interface with differential signal transmission line. 
       FIG. 4  is a flowchart of a USB interface according to a preferred embodiment of the present invention. As shown in  FIG. 4 , a process includes the following steps (the following steps are based on the embodiment that the voltage-variable component  313  is disposed on the DP signal transmission  305  as shown in  FIG. 3 , while that on the DN signal transmission  307  is similar, and is omitted herein). 
     In step  401 , it is determined whether the electronic device is coupled to any electronic apparatuses (e.g., in the embodiment shown in  FIG. 3 , the electronic device  300  includes a processor  304 , the processor  304  will determine whether the electronic device  300  is coupled to any other electronic apparatus via the USB interface), in an alternative embodiment, it can be implemented by determining whether the power line has received voltage. If true, the process proceeds to step  403 ; else, the process has no response. Please note that the schematic diagram in  FIG. 3  is only an exemplary embodiment, and the present invention is not limited in the structure disclosed in  FIG. 3 . 
     In step  403 , it is determined whether the DP signal transmission line is at a high level (i.e., determining whether the logic voltage level is “1” can be performed by the processor  304 ). If true, the process proceeds to step  405 ; else, the process proceeds to step  407 . 
     In step  405 , it is determined whether the electronic device is coupled to a charger. 
     In step  407 , it is determined whether the electronic device is coupled to a PC device. 
     In step  409 , after the processor  304  confirms that the electronic device  300  is coupled to the PC device  315 , the switch component  321  (the switching method is achieved, for example, by controlling the value of the register, which is similar to that described above) is switched, enabling the DP signal transmission line  305  to be coupled to the voltage source V DD  via the boost resistor  309 , such that the USB interface  302  operates in a high speed state. As described above, the voltage-variable component  313  can be disposed on the DN signal transmission line  307  instead of the DP signal transmission line  305 . Furthermore, the switch component  321  can also be disposed on the DN signal transmission line  307  instead of the DP signal transmission line  305 . 
     Please note that if the resistance of the voltage-variable component  313  is big enough to distinguish which electronic apparatus (a charger or a PC device) is coupled to the electronic device  300 , and enough for the USB interface to normally operate in a corresponding high speed state or low speed state, then the step  409  may be eliminated. 
     According to the embodiments described above, the present invention is capable of determining which electronic apparatus (a charger or a PC device) is coupled to the electronic device  300  without an additional circuit in the charger; furthermore, the present invention is capable of switching the USB interface to the signal transmission line of the electronic device after the electronic apparatus is distinguished, enabling the USB interface to operate in a corresponding high speed state or low speed state. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not to be limited to the above embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.

Technology Category: g