Abstract:
A signal transceiving circuit, comprising: a receiver, for receiving a input signal; a transmitter, for transmitting an output signal; and a resistance circuit, for omitting the noise caused by the output signal to the input signal. The resistance circuit comprises: a voltage transferring circuit, for generating a voltage transferred signal, and a voltage dividing circuit, for voltage dividing the voltage transferred signal and the output signal, such that the voltage generated at the receiver is cancelled by the voltage generated by the voltage transferred signal at the transceiver. A noise reduction circuit that can be utilized in this signal transceiving circuit is also disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the provisional application, which is U.S. Provisional Application No. 61/248,434, filed Oct. 3, 2009, and is included herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a signal transceiving circuit, and particularly relates to a signal transceiving circuit that can omit the noise caused by nearby transmitters. The present invention also relates to a noise reduction circuit that can be utilized to the signal transceiving circuit. 
         [0004]    2. Description of the Prior Art 
         [0005]      FIG. 1  is a prior art signal transceiving circuit. As shown in  FIG. 1 , the transmitter  101  outputs an output signal OS to a receiver  105  of another transceiving circuit via a cable  103 , and the receiver  107  receives an input signal IS via the cable  103 . However, in a current transceiving circuit, a group consisted of a transmitter  101  and a receiver  107  always shares the same transmitting lines, as shown in  FIG. 1 . In this situation, the transmitter  101  can be regarded as a nearby transmitter for the receiver  107 . Such structure will cause the output signal OS to generate noise to the input signal IS, and the quality for the receiver  107  to receive the input signal IS is also affected. 
         [0006]    Some inventions are developed to solve this problem. For example, the U.S. patent with Pat. No. 6,744,831 has disclosed such technology. As shown in FIG. 3 thereof, this patent utilizes a device 88 to counteract the noise caused by the output signal to the input signal. However, such kind of prior art needs extra circuits and accurate control to omit noise. By this way, a larger circuit area is needed, and design complexity, production cost also increase. 
       SUMMARY OF THE INVENTION 
       [0007]    Therefore, one objective of the present invention is to provide a signal transceiving circuit, which can utilize a simple circuit to counteract with the noise caused by the nearby transmitter. Besides, the present invention also discloses the noise reduction circuit that is utilized in the transceiving circuit. 
         [0008]    One embodiment of the present invention discloses a signal transceiving circuit, which comprises: a receiver, for receiving an input signal; a transmitter, for transmitting an output signal; and a resistance circuit for omitting noise that the output signal caused to the input signal. The resistance circuit comprises: a voltage transferring circuit, for generating a voltage transferring signal according to the output signal; and a voltage dividing circuit, for voltage-dividing the voltage transferring signal and the output signal, such that a voltage that the output signal generates at the receiver will be counteracted with a voltage that the voltage transferred signal generates at the receiver. 
         [0009]    Another embodiment discloses a noise reduction circuit, which outputs an output signal from a signal outputting source and receives an input signal from a receiver. The noise reduction circuit comprises: a voltage transferring circuit, for generating a voltage transferring signal according to the output signal; and a voltage dividing circuit, for voltage dividing the voltage transferring signal and the output signal, such that a voltage that the output signal generates at the receiver will be counteracted with a voltage that the voltage transferred signal generates at the receiver. 
         [0010]    Another embodiment discloses a signal transceiving circuit, which is coupled to a signal input source comprising a first input terminal and a second input terminal. The signal transceiving circuit comprises: a receiver, for receiving an input signal; a transmitter, comprising a first transmitting terminal and a second transmitting terminal, and for transmitting a differential output signal via the first transmitting terminal and the second transmitting terminal; and a resistance circuit, for omitting noise that the output signal caused to the input signal, comprising. The resistance circuit comprises a first resistance device, having one terminal coupled to the second transmitting terminal, and the other terminal coupled to the first input terminal; a second resistance device, having one terminal coupled to the first transmitting terminal, and the other terminal coupled to the second input terminal; a first voltage dividing circuit, coupled between the first transmitting terminal and the first receiving terminal; and a second voltage dividing circuit, coupled between the second transmitting terminal and the second receiving terminal. 
         [0011]    Via above-mentioned embodiments, only a resistance circuit is needed to counteract the noise that a nearby transmitter causes to the receiver, thus no complex circuit and tough circuit control. By this way, circuit area can decrease, and the cost for manufacturing and design can decrease. 
         [0012]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a prior art signal transceiving circuit. 
           [0014]      FIG. 2  is a circuit diagram illustrating a signal transceiving circuit  200  according to one embodiment of the present invention. 
           [0015]      FIG. 3  is a circuit diagram illustrating detail structures of the signal transceiving circuit shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
         [0017]      FIG. 2  is a circuit diagram illustrating a signal transceiving circuit  200  according to one embodiment of the present invention. As shown in  FIG. 2 , the signal transceiving circuit  200  comprises a transmitter  201 , a receiver  203  and a resistance circuit  205 . The receiver  201  receives an input signal IS. The transmitter  201  transmits an output signal OS. The resistance circuit  205  is coupled to a first input terminal  216  and a second input terminal  218  of a cable  215 . The resistance circuit  205  can be consisted of resistors, or other active/passive devices having resistance characteristics, to omit the noise that the output signal OS causes to the input signal IS. In this embodiment, the signal transceiving circuit  200  utilizes a differential signal, thus the transmitter  201  includes a first transmitting terminal  207  and a second transmitting terminal  209 , and the receiver  203  includes a first receiving terminal  211  and a second receiving terminal  213 . However, it does not indicate that the concept of the present invention is limited to be utilized to a signal transceiving circuit utilizing a differential signal. 
         [0018]    Additionally, in the embodiment shown in  FIG. 2 , the cable is a HDMI (High Definition Multimedia Interface) cable. Resistors  217 ,  219 , which are  10  ohm in this embodiment, are provided between the transmitter  201  and the voltage source Vcc. Also, capacitors  227  and  229  are provided between the cable  215  and the resistance circuit  205 . Additionally, the transmitter  201  includes two switches  223 ,  225  and a current source  221 . It should be noted that, these detail structures are only for example and do not mean to limit the scope of the present invention. For example, the transmitter  201  can be different kinds of transmitters, and the cable  215  can be other kinds of cables. 
         [0019]      FIG. 3  is a circuit diagram illustrating detail structures of the signal transceiving circuit shown in  FIG. 2 . In this embodiment, the resistance circuit  205  is consisted of resistors. As shown in  FIG. 3 , the resistance circuit  205  comprises a first resistor  301 , a second resistor  303 , a third resistor  305 , a fourth resistor  307 , a fifth resistor  309  and a sixth resistor  311 . A first terminal of the first resistor  301  is coupled to the second transmitting terminal  209 , and a second terminal thereof is coupled to the cable  215 . A first terminal of the second resistor  303  is coupled to the transmitting terminal  207 . A first terminal of the third resistor  305  is coupled to a second terminal of the second resistor  303 , and a second terminal thereof is coupled to the cable  215 . A first terminal of the fourth resistor  307  is coupled to the transmitting terminal  207 , and a second terminal thereof is coupled to the cable  215 . A first terminal of the fifth resistor  309  is coupled to the second transmitting terminal  209 . A first terminal of the sixth resistor  311  is coupled to a second terminal of the fifth resistor  309 , and a second terminal thereof is coupled to the cable  215 . The second terminal of the second resistor  303  is further coupled to the second receiving terminal  213 , and the second terminal of the fifth resistor  309  is further coupled to the first receiving terminal  213 . 
         [0020]    In one embodiment, the second resistor  303  has substantially the same resistance value (9K ohm) with the resistance value of the fifth resistor  309 , and the third resistor  305  has substantially the same resistance value (5K ohm) with the resistance value of the sixth resistor  311 . That is, the ratio between the resistance values of the second resistor  303  and the fifth resistor  309 , and the resistance value of the third resistor  305  and sixth resistor  309  is 9:5. Besides, the first resistor  301  has substantially the same resistance value (40 ohm) with the resistance value of the fourth resistor  307 . Also, the equivalent resistors  231  and  233  of the cable  215  are both  50  ohm. That is, the ratio between the resistance values of the first resistor  301  and fourth resistor  307 , and the resistance value of the equivalent resistors  231  and  233  is 4:5. The equivalent resistor  231  is the cable equivalent resistor of looking from the transmitting paths Tx−( 301 ,  303 ,  305 ) into cable. The equivalent resistor  233  is the cable equivalent resistor of looking from the transmitting paths Tx+( 307 ,  309 ,  311 ) into cable. It should be noted that, in the embodiment shown in  FIG. 3 , for the resistance circuit  205 , the transmitter  201  can be regarded as a signal output source to output the output signal OS to the resistance circuit  205 . Besides, the cable  215  can be regarded as a signal input source, to output the input signal IS to the resistance circuit  205 . It should be noted that the ratio between the resistance values of the second resistor  303  and fifth resistor  309 , and which of the third resistor  305  and sixth resistor  309 , and the ratio between the resistance values of the first resistor  301  and fourth resistor  307  and which of the equivalent resistors  231  and  233  can be other values except above-mentioned 9:5 and 4:5. Also, all resistors can be replaced with other active devices that can form resistance (ex. MOSFET). 
         [0021]    The following description describes why the embodiment shown in  FIG. 3  can omit the noise that the output signal OS causes to the input signal IS. Please notes the following embodiment only considers AC component but considers no DC component. 
         [0022]    Suppose 
         [0000]      Vtxp=Vtx  (equation 1)
 
         [0000]    then 
         [0000]      Vtxn=−Vtx  (equation 2)
 
         [0023]    Vtxp and Vtxn are the voltages at the first transmitting terminal  207  and the second transmitting terminal  209 . 
         [0024]    Since the resistance values of the second resistor  303 , the third resistor  305 , the fifth resistor  309  and the sixth resistor  311  (5K ohm and 9K ohm) are much larger than the resistance value of the first resistor  301 , the fourth resistor  307  and the cable equivalent resistors  231 ,  233  (40 ohm and 50 ohm) , the currents flowing through the second resistor  303 , the third resistor  305 , the fifth resistor  309  can be ignored. 
         [0000]      Vcp=−Vtx*R231/(R231+R301)=−Vtx*50/(40+50)  (equation 3)
 
         [0000]      Vcn=Vtx*R233/(R233+R307)=Vtx*50/(40+50)  (equation 4)
 
         [0025]    Vcp and Vcn are respectively the voltages at a second terminal of the first resistor  301  and a second terminal of the fourth resistor  307 . 
         [0026]    Then, voltages can be computer from relations between each resistor. 
         [0000]      Vrxp=Vtxn*R 311 /(R 311 +R 309 )+Vcn*R 309 /(R 311 +R 309 ) =Vtxn*5K/(5K+9K)+Vcn*9K/(5K+9K)  (equation 5)
 
         [0000]      Vrxn=Vtxp*R 305 /(R 305 +R 303 )+Vcp*R 303 /(R 305 +R 303 ) =Vtxp*5K/(5K+9K)+Vcp*9K/(5K+9K)  (equation 6)
 
         [0027]    Vrxp and Vrxn are respectively the voltages at the first receiving terminal  211  and the second receiving terminal  213 . 
         [0028]    After that, the equations (1) (3) are substituted to equation (6), and equations (2) (4) are substituted to equation (5). 
         [0029]    Vrxp=−Vtx*5K/(5K+9K)+Vtx*50/(40+50)*9K/(5K+9K)=0 
         [0030]    Vrxn=Vtx*5K/(5K+9K)−Vtx*50/(40+50)*9K/(5K+9K)=0 
         [0031]    By this way, Vtx can be totally omitted, to acquire the result that Vrxp=Vrxn=0. 
         [0032]    According to above mentioned description, the noise that the output signal causes at the receiving terminal can be completely omitted. 
         [0033]    In view of above-mentioned equations, the first resistor  301  and the fourth resistor  307  can be regarded as a voltage transferring circuit, since the first resistor  301  and the fourth resistor  307  can transfer voltages (decrease voltages). Such voltage transferring circuit can match the cable equivalent resistors  231 ,  233  to generate voltages Vcp and Vcn, which are related with the voltage Vtxn at the second transmitting terminal  209  and the voltage Vtxp at the first transmitting terminal  207 , at a first terminal of the first resistor  301  and a first resistor at the fourth resistor  307  (equations 3, 4). It should be noted, the voltage transferring circuit discussed here is not limited to a single resistance device, any circuit that can cooperate with the cable equivalent resistors  231 ,  233  to generate a voltage dividing function, should be included in the range of the present application. 
         [0034]    Then, the second resistor  303 , the third resistor  305 , the fifth resistor  309  and the sixth resistor  311  match with each other to generate divided voltages for the voltages Vtxn and Vcn, and the voltages Vtxp and Vcp (equations 5, 6). Thus the divided voltages of the voltages Vtxn and Vcn can be counteracted with each other, and the divided voltages of the voltages Vtxp and Vcp can be counteracted with each other. Therefore, the second resistor  303 , the third resistor  305 , the fifth resistor  309  and the sixth resistor  311  can be regarded as a voltage dividing circuit. Alternatively, the second resistor  303 , and the third resistor  305  can be regarded as a voltage dividing circuit, and the fifth resistor  309  and the sixth resistor  311  can be regarded as another voltage dividing circuit, to voltage-divide the voltage transferring signal and the output signal, such that the output signal generated at the receiver can be counteracted by a voltage that the voltage transferred signal generates at the receiver. 
         [0035]    The following concept discloses the signals received by the receiver. 
         [0000]      Vcp=Vsig  (equation 1)
 
         [0000]      Vcn=−Vsig  (equation 2)
 
         [0036]    Vsig and −Vsig indicate the positive and negative voltages of the input signal In generated at the differential signal transmission line. 
         [0037]    Since the resistance values of the second resistor  303 , the third resistor  305 , the fifth resistor  209  and the sixth resistor  311  (5K ohm and 9K ohm) are much larger than the resistance value of the first resistor  301 , the fourth resistor  307  and the cable equivalent resistors  231 ,  233  (40 ohm and 50 ohm), the currents flowing through the second resistor  303 , the third resistor  305 , the fifth resistor  309  can be ignored. 
         [0000]      Vtxp=−Vsig*R 217 /(R 307 +R 217 )=−Vsig*10/(40+10)  (equation 3)
 
         [0000]      Vtxn=Vsig*R 219 /(R 301 +R 219 )=Vsig*10/(40+10)  (equation 4)
 
         [0038]    Then, voltages can be computer from relations between each resistor. 
         [0000]      Vrxp=Vtxn*5K/(5K+9K)+Vcn*9K/(5K+9K)  (equation 5)
 
         [0000]      Vrxn=Vtxp*5K/(5K+9K)+Vcp*9K/(5K+9K)  (equation 6)
 
         [0039]    Then the equations (1) (3) are substituted to equation (6), and equations (2) (4) are substituted to equation (5). 
         [0000]      Vrxp=Vsig*10/(40+10)*5K/(5K+9K)−Vsig*9K/(5K+9K)=−Vsig*4/7
 
         [0000]      Vrxn=−Vsig*10/(40+10)*5K/(5K+9K)+Vsig*9K/(5K+9K)=Vsig*4/7
 
         [0040]    Via these equations, it is clear that the amplitude of the signal received by the receiver  203  is a ratio to the input signal In, but is not affected by the output signal of the transmitter  201 . 
         [0041]    Via above-mentioned embodiments, only a resistance circuit is needed to counteract the noise that a nearby transmitter causes to the receiver, thus no complex circuit and tough circuit control. By this way, circuit area can decrease, and the cost for manufacturing and design can decrease. 
         [0042]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.