Abstract:
A differential signal transmission system includes m different voltage/current supplies, n transmission end, and a controller. The controller includes m×n switches. Each of the switches is coupled between a voltage/current supply and a transmission end. The controller controls the switches to turn on or off for coupling each transmission end to one of the different voltage/current supplies so as to carry the voltage of the coupled voltage supply onto the transmission end according to the transmitting data. The sum of the voltage differences among the transmission ends is 0.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a transmission system of differential signals, and more particularly, to a transmission system of a differential signal group. 
   2. Description of the Prior Art 
     FIG. 1  is a diagram illustrating a conventional differential signal transmission system  100 . The transmission end of the conventional differential signal transmission system  100  comprises a transmission device  110  for transmitting a pair of voltage signals according to the transmitting data (one bit, 0 or 1) through the transmission line pair to the comparator  120  of the receiving end. The comparator  120  compares the voltages of the input ends A and B for generating the received data (0 or 1). For example, when data “0” is transmitted, the transmission device  110  transmits −5 volts on the transmission line A, and +5 volts on the transmission line B. Thus, the comparator  120  compares the voltages on the transmission lines A and B (V A &lt;V B ) and outputs data “0”. In this way, the differential transmission is completed. The reason for the conventional transmission system  100  utilizing differential signals is that the differential signals of the same pair have the same common-mode noises and therefore the differential signals of the same pair possess better capability of resisting noises. And because in the differential signal pair, a voltage change in one differential signal has the same amplitude as a voltage change in the other differential signal (and inversed), the electromagnetic interference (EMI) generated by the voltage changes can be reduced. However, in the conventional transmission system  100 , a pair of transmission lines only transmits one bit at one time. Therefore, when the data transmission bandwidth requirement becomes substantially large, much more pairs of transmission lines are needed, which costs space and expense. 
   SUMMARY OF THE INVENTION 
   The present invention provides a differential signal transmission system for transmitting data. The differential signal transmission system comprises m different reference signal supplies, n transmission ends, and a controller, where m and n are positive integers. The controller includes (m×n) switches. Each switch is coupled between one of the m reference signal supplies and one of the n transmission ends. The controller controls the (m×n) switches for coupling each of the n transmission ends to one of the m reference signal supplies so as to enable each of the n transmission ends to carry a corresponding reference signal according to the data. A sum of signal differences among the n transmission ends is 0, and m≧n, and n≧3. 
   These and other objectives of the present invention will no doubt become apparent 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 
       FIG. 1  is a diagram illustrating a conventional differential signal transmission system. 
       FIG. 2  is a diagram illustrating a differential signal transmission system according to a first embodiment of the present invention. 
       FIG. 3  is a diagram illustrating the transmission of  FIG. 2 . 
       FIG. 4  is a diagram illustrating a differential signal transmission system according to a second embodiment of the present invention. 
       FIG. 5  is a diagram illustrating a differential signal transmission system according to a third embodiment of the present invention. 
       FIG. 6  is a diagram illustrating the transmission of  FIG. 5 . 
       FIG. 7  is a table illustrating the operation of  FIG. 5 . 
   

   DETAILED DESCRIPTION 
     FIG. 2  is a diagram illustrating a differential signal transmission system  200  according to a first embodiment of the present invention. As shown in  FIG. 2 , the transmission system  200  utilizes three transmission lines A, B, and C for transmission. The transmission end of the transmission system  200  comprises a controller  210 , three different reference signal supplies V 1 , V 2 , and V 3 , and nine switches S 1A , S 2A , S 3A , S 1B , S 2B , S 3B , S 1C , S 2C , and S 3C . In the transmission system  200 , the reference signal supplies V 1 , V 2 , and V 3  are realized with three difference voltage supplies. The controller  210  controls the switches S 1A , S 2A , S 3A , S 1B , S 2B , S 3B , S 1C , S 2C , and S 3C  to respectively turn on or off according to the transmitting data. In this way, the transmission lines A, B, and C are respectively coupled to one of the voltage supplies V 1 , V 2 , and V 3 . The voltage supplies V 1 , V 2 , and V 3  can be DC or AC signals. Consequently, the transmission lines A, B, and C respectively carry voltage V A , V B , and V C  to the receiving end of the transmission system  200 . The receiving end of the transmission system  200  comprises 3 comparators  221 ,  222 , and  223 , and a decoder  230 . The comparators  221 ,  222 , and  223  are disposed respectively for comparing voltages V A , V B , and V C , and accordingly generating compared results to the decoder  230 . The decoder  230  decodes the received data according to the compared results of the comparators  221 ˜ 223 . The sum of the voltage differences among the voltages V A , V B , and V C  is 0 (ΔV AB +ΔV BC +ΔV CA =0). 
   According to the present invention, in the transmission end of the transmission system  200 , the number of voltage supplies can be greater than or equal to the number of transmission lines. And because the sum of the voltage differences among the transmission lines is 0 volts, the data transmission can be completed with better transmission quality. 
     FIG. 3  is a diagram illustrating the transmission of  FIG. 2 . Under the condition that the sum of the voltages of the transmission lines A, B, and C is 0 volts, the transmission system  200  can transmit 2.5 bits of data ( 1 ,  2 ,  3 ,  4 ,  5 , and  6 ). It is assumed that the voltage V 1  is +1 volt, the voltage V 2  is 0 volts, and the voltage V 3  is −1 volt, and consequently the transmission of data  1 - 6  is achieved as shown in  FIG. 3 . 
     FIG. 4  is a diagram illustrating a differential signal transmission system  400  according to a second embodiment of the present invention. As shown in  FIG. 4 , the transmission system  400  also utilizes three transmission lines A, B, and C to transmit data, which is similar to the transmission system  200 . The difference between the transmission systems  400  and  200  is that the transmission system  400  transmits data by current rather than voltage. That is, the reference signal supplies are realized with current supplies I 1 , I 2 , and I 3 . Therefore, the transmission end of the transmission system  400  comprises a controller  410 , three different current supplies I 1 , I 2 , and I 3 , and nine switches S 1A , S 2A , S 3A , S 1B , S 2B , S 3B , S 1C , S 2C , and S 3C . The controller  410  controls the switches S 1A , S 2A , S 3A , S 1B , S 2B , S 3B , S 1C , S 2C , and S 3C  respectively to turn on or off according to the transmitting data. In this way, the transmission lines A, B, and C are respectively coupled to one of the current supplies I 1 , I 2 , and I 3 . The current supplies I 1 , I 2 , and I 3  can be DC or AC signals. Consequently, the transmission lines A, B, and C respectively carry currents I A , I B , and I C  to the receiving end of the transmission system  400 . The receiving end of the transmission system  400  comprises three current/voltage converters  441 ,  442 , and  443  for respectively converting the currents I A , I B , and I C  into the voltages V A , V B , and V C  besides three comparators  421 ,  422 , and  423 , and a decoder  430 . The function of the comparators  421 ˜ 423  and the decoder  430  is the same as that of the comparators  221 - 223  and the decoder  230 . The sum of the current differences among the currents I A , I B , and I C  is 0 (that is, ΔI AB +ΔI BC +ΔI CA =0). 
   According to the present invention, in the transmission end of the transmission system  400 , the number of current supplies does not necessarily need to be the same as the number of transmission lines. Instead, the number of current supplies has to be greater than or equal to the number of transmission lines. As long as the sum of the current differences among the transmission lines is 0 amperes, the data transmission can be completed with improved transmission quality. 
     FIG. 5  is a diagram illustrating a differential signal transmission system  500  according to a third embodiment of the present invention. As shown in  FIG. 5 , the transmission system  500  utilizes four transmission lines A, B, C, and D for transmission. The transmission end of the transmission system  500  comprises a controller  510 , four different reference signal supplies V 1 , V 2 , V 3 , and V 4 , and sixteen switches S 1A , S 2A , S 3A , S 4A , S 1B , S 2B , S 3B , S 4B , S 1C , S 2C , S 3C , S 4C , S 1D , S 2D , S 3D , and S 4D . The reference signal supplies V 1 , V 2 , V 3 , and V 4  are realized with four different voltage supplies. The controller  510  controls the switches S 1A , S 2A , S 3A , S 4A , S 1B , S 2B , S 3B , S 4B , S 1C , S 2C , S 3C , S 4C , S 1D , S 2D , S 3D , and S 4D  to respectively turn on or off according to the transmitting data. In this way, the transmission lines A, B, C, and D are respectively coupled to one of the voltage supplies V 1 , V 2 , V 3 , and V 4 . The voltage supplies V 1 , V 2 , V 3 , and V 4  can be DC or AC signals. Consequently, the transmission lines A, B, C, and D respectively carry voltage V A , V B , V C , and V D  to the receiving end of the transmission system  500 . The receiving end of the transmission system  500  comprises 6 comparators  521 ,  522 ,  523 ,  524 ,  525 , and  526 , and a decoder  530 . The comparators  521 ˜ 526  are disposed respectively for comparing voltages V A , V B , V C , and V D , thereby generating compared results to the decoder  530 . The decoder  530  decodes the received data according to the compared results of the comparators  521 - 523 . The sum of the voltage differences among the voltages V A , V B , V C , and V D  is 0 (that is, ΔV AB +ΔV BC +ΔV CD +ΔV DA +ΔV DB +ΔV AC =0). 
   According to the present invention, in the transmission end of the transmission system  500 , the number of voltage supplies has to be greater than or equal to the number of transmission lines. And because the sum of the voltage differences among the transmission lines is 0 volts, the data transmission can be completed with better transmission quality. 
     FIG. 6  is a diagram illustrating the transmission of  FIG. 5 . Under the condition that the sum of the voltages of the transmission lines A, B, C, and D is 0 volts, the transmission system  200  can transmit 4.5 bits of data ( 1 - 24 ). It is assumed that the voltage V 1  is +2 volts, the voltage V 2  is +1 volt, the voltage V 3  is −1 volt, and the voltage V 4  is −2 volts, and consequently, the transmission of data  1 - 24  can be achieved as shown in  FIG. 5 . 
     FIG. 7  is a table illustrating the operation of  FIG. 5 . As shown in  FIG. 7 , each transmitting data activates the controller  510  to turn on corresponding switches, and thus the voltages of the voltage supplies V 1 -V 4  are respectively transmitted to the transmission lines A, B, C, and D. For example, when the data “1” is transmitted, the controller  510  turns on the switches S 1A , S 2B , S 3C , and S 4D , and turns off the rest of the switches. In this way, the voltage V A  is +2 volts because the transmission line A is coupled to the voltage supply V 1  through the switch S 1A ; the voltage V B  is +1 volt because the transmission line B is coupled to the voltage supply V 2  through the switch S 2B ; the voltage V C  is −1 volt because the transmission line C is coupled to the voltage supply V 3  through the switch S 3C ; the voltage V D  is −2 volts because the transmission line D is coupled to the voltage supply V 4  through the switch S 4D . The sum of the voltage differences among the transmission lines A, B, C, and D is 0 (or, in other words, ΔV AB +ΔV BC +ΔV CD +ΔV DA +ΔV DB +ΔV AC =1+2+1+(−4)+(−3)+3=0). The voltage V A  is higher than V B  (+2&gt;+1), and thus the comparator  521  outputs a result of “1”; the voltage V A  is higher than V C  (+2&gt;−1), and thus the comparator  522  outputs a result of “1”; voltage V A  is higher than V D  (+2&gt;−2), and thus the comparator  523  outputs a result of “1”; the voltage V B  is higher than V C  (+1&gt;−1), and thus the comparator  524  outputs a result of “1”; the voltage V B  is higher than V D  (+1&gt;−2), and thus the comparator  525  outputs a result of “1”; the voltage V C  is higher than V D  (−1&gt;−2), and thus the comparator  526  outputs a result of “1”. The decoder  530  receives the results “1”, “1”, “1”, “1”, “1”, and “1” respectively of the comparators  521 - 526  and consequently determines the received data is “1”. In this way, the data transmission of the differential signal transmission system  500  is completed. 
   Therefore, in the embodiments discussed above, the transmission system with three transmission lines transmits data  1 - 6 , and the transmission system with four transmission lines transmits data  1 - 24 . Similarly, the transmission system with five transmission lines can transmit data  1 - 120 , which consequently raises the data transmission rate. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made.