Abstract:
A baseline wandering correction device for correcting baseline wandering of signals at a first output terminal and a second output terminal of a receiver includes: a control circuit for outputting a control signal according to voltages of the first and the second output terminals and a second threshold value; a voltage generation unit coupled to the control circuit for outputting a control voltage according to the control signal, the voltages of the first and the second output terminals, and a first threshold value; and a compensation current source coupled to the voltage generation unit for outputting a compensation current to the receiver according to the control voltage to correct the baseline wandering.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to network communications, and more particularly, to baseline wandering correction. 
   2. Description of the Prior Art 
   The phenomenon of baseline wandering at a receiver, in the context of Ethernet network communications or the like, has existed for a long time. It is a problem that those skilled in the art continue trying to resolve. Please refer to Taiwan Patent No. 497,334, Taiwan Patent No. 545,016, and U.S. Pat. No. 6,433,608 for related technology information on baseline wandering correction, the contents of all of which are incorporated herein by reference. 
   According to U.S. Pat. No. 6,433,608, if the goal of baseline wandering correction is to be achieved, certain conditions described by the following equations should be satisfied: 
   
     
       
         
           
             
               
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                             R 
                             o 
                           
                           
                             2 
                             ⁢ 
                             L 
                           
                         
                         = 
                         
                           1 
                           
                             
                               R 
                               x 
                             
                             ⁢ 
                             C 
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           4 
                           ⁢ 
                           
                             R 
                             ⁡ 
                             
                               ( 
                               gmx 
                               ) 
                             
                           
                           ⁢ 
                           
                             I 
                             c 
                           
                         
                         = 
                         
                           V 
                           
                             R 
                             x 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   
                     
                       ( 
                       1 
                       ) 
                     
                   
                 
                 
                   
                     
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                       2 
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   where definitions of related parameters and derivations of the equations have been disclosed and therefore can be found in U.S. Pat. No. 6,433,608. Detailed explanations are thus not repeated herein for brevity. 
   However, as the parameters L and Ro in equation (1) respectively represent an inductance value of a transformer and a resistance value of a matching resistor, and as the transformer and the matching resistor are stand-alone components, it is difficult to accurately control values of the parameters L and Ro, and especially the value of the parameter L. When the parameter L or the parameter Ro deviates from nominal value for any particular reason, such variation of manufacturing process or ambient temperature, the condition described by equation (1) becomes difficult to maintain, and therefore the baseline wandering phenomenon can not be effectively corrected. 
   SUMMARY OF THE INVENTION 
   It is an objective of the claimed invention to provide baseline wandering correction devices and methods to alleviate the above-mentioned influences from process variation or temperature variation. 
   It is an objective of the claimed invention to provide baseline wandering correction devices and methods to correct baseline wandering in a real time fashion. 
   According to one embodiment of the claimed invention, a baseline wandering correction device for correcting baseline wandering of signals at a first output terminal and a second output terminal of a receiver is disclosed. The baseline wandering correction device comprises: a control circuit for outputting a control signal according to voltages of the first and the second output terminals and a second threshold value; a voltage generation unit coupled to the control circuit for outputting a control voltage according to the control signal, the voltages of the first and the second output terminals, and a first threshold value; and a compensation current source coupled to the voltage generation unit for outputting a compensation current to the receiver according to the control voltage to correct the baseline wandering. 
   According to one embodiment of the claimed invention, a baseline wandering correction method for correcting baseline wandering of signals at a first output terminal and a second output terminal of a receiver is disclosed. The baseline wandering correction method comprises: outputting a control signal according to voltages of the first and the second output terminals and a second threshold value; outputting a control voltage according to the control signal, the voltages of the first and the second output terminals, and a first threshold value; and outputting a compensation current to the receiver according to the control voltage to correct the baseline wandering. 
   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 
       FIG. 1  is a schematic view of a receiving device according to one embodiment of the present invention. 
       FIG. 2  is a diagram of a voltage signal generator according to one embodiment of the present invention. 
       FIG. 3  is a diagram of the impedance shown in  FIG. 2 . 
       FIG. 4  is a flowchart of a baseline wandering correction method according to one embodiment of the present invention. 
       FIG. 5  is a schematic view of a receiving device according to another embodiment of the present invention. 
       FIG. 6  is a diagram of a voltage signal generator according to another embodiment of the present invention. 
       FIG. 7  is a diagram of the impedance shown in  FIG. 6 . 
       FIG. 8  is a diagram of a voltage signal generator according to yet another embodiment of the present invention. 
       FIG. 9  is a diagram of the impedance shown in  FIG. 8 . 
       FIG. 10  is a diagram of a voltage signal generator according to yet another embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 1 .  FIG. 1  is a schematic view of a receiving device  200  according to one embodiment of the present invention, where operation of the receiver  110  is well known in the art, such as those described in U.S. Pat. No. 6,433,608, and therefore is not explained in detail herein. As shown in  FIG. 1 , the receiving device  200  comprises a baseline wandering correction device  201  comprising a voltage signal generator  210  and a compensation current source  220 . The voltage signal generator  210  comprises a control circuit  212  and a voltage generation unit  214 , where the control circuit  212  outputs a control signal Ctrl 1  to the voltage generation unit  214  and the compensation current source  220  according to a threshold value, which is a reference voltage Voffset in this embodiment, and according to voltages of output terminals Vop and Von of the receiver  110 , and in particular, variations of the voltages of the output terminals Vop and Von. The voltage generation unit  214  outputs a control voltage Vx to the compensation current source  220  according to the control signal Ctrl 1 , the variations of the voltages of the output terminals Vop and Von of the receiver  110 , and another threshold value, which is another reference voltage Vth in this embodiment. The compensation current source  220  then outputs a compensation current Ix to the receiver  110  according to the control signal Ctrl 1  and the control voltage Vx to correct the baseline wandering. 
   In this embodiment, in order to satisfy the conditions described by equations (1) and (2) mentioned above to effectively correct the baseline wandering phenomenon, the control circuit  212  adjusts parameter(s) of at least one of the components in the voltage generation unit  214  and a transconductance value gmx of the compensation current source  220  by utilizing the control signal Ctrl 1 , to control the compensation current Ix outputted by the compensation current source  220 . 
   Please refer to  FIG. 2 ,  FIG. 3 , and  FIG. 4 .  FIG. 2  is a diagram of a voltage signal generator according to one embodiment of the present invention, where the architecture shown in  FIG. 2  can be applied to the embodiment shown in  FIG. 1 , and  FIG. 3  is a diagram of the impedance  35   a  shown in  FIG. 2 .  FIG. 4  is a flowchart of a baseline wandering correction method according to one embodiment of the present invention, where the method shown in  FIG. 4  can be applied to the embodiment shown in  FIG. 2 . As shown in  FIG. 2 , the control circuit  310  comprises two comparators  312  and  314 , a charge pump  316 , and a voltage-to-current (V/I) conversion circuit  318 , where the charge pump  316  and the V/I conversion circuit  318  are well known in the related art, and therefore are not explained in detail herein. Similarly, operations of the current sources  31 - 34 , the two comparators  36 - 37 , and the switches  38 - 39  of the voltage generation unit  320  are described in U.S. Pat. No. 6,433,608, and therefore are not explained in detail herein. The control circuit  310  and the voltage generation unit  320  mentioned above respectively correspond to the control circuit  212  and the voltage generation unit  214  shown in  FIG. 1 . Different architecture of the control circuit and the voltage generation unit can be applied to other embodiments of the present invention. 
   Please refer to  FIG. 2  and  FIG. 4 . The comparator  314  outputs a comparison result S_Vdown according to the reference voltage Voffset and a voltage difference of the output terminals Vop and Von of the receiver  110 , where the voltage difference utilized by the comparator  314  can be referred to as (Vop−Von), i.e., the voltage of the output terminal Vop subtracting the voltage of the output terminal Von. In addition, the comparator  312  outputs a comparison result S_Vup according to the reference voltage Voffset and another voltage difference of the output terminals Vop and Von of the receiver  110 , where the voltage difference utilized by the comparator  312  can be referred to as (Von−Vop), i.e., the voltage of the output terminal Von subtracting the voltage of the output terminal Vop. The charge pump  316  outputs an output voltage V 1  to the V/I conversion circuit  318  according to the comparison result S_Vdown and/or the comparison result S_Vup, where the charge pump  316  decreases a value of the output voltage V 1  when the voltage difference (Vop−Von) is greater than the reference voltage Voffset, increases the value of the output voltage V 1  when the voltage difference (Von−Vop) is greater than the reference voltage Voffset, and maintains the value of the output voltage V 1  when the voltage difference (Vop−Von) falls within the range [−Voffset, +Voffset]. 
   In addition, the V/I conversion circuit  318  receives the output voltage V 1  and converts the output voltage V 1  into a control current I 1  to be outputted to the impedance  35   a  of the voltage generation unit  320 . As shown in  FIG. 3 , the impedance  35   a  comprises a capacitor  352  and a current source module  351   g , which are arranged in parallel. In this embodiment, the current source module  351   g  comprises K control current sources  351 - 1 ,  351 - 2 , . . . , and  351 -K, where an input terminal and an output terminal of each control current source are coupled to one terminal of the capacitor  352 , and another input terminal and another output terminal of the control current source is coupled to the other terminal of the capacitor  352 . The control circuit  310  controls the transconductance value gmx of the compensation current source  220  and a transconductance value gm of each of the control current sources  351 - 1 ,  351 - 2 , . . . , and  351 -K according to the magnitude of the control current I 1 . The number of control current sources within the current source module  351   g  can be one or more, when the ratio of an equivalent transconductance value (K*gm) of the current sources  351 - 1 ,  351 - 2 , . . . , and  351 -K that are arranged in parallel to the transconductance value gmx of the compensation current source  220  can be maintained to a predetermined value. 
   An equivalent resistance value corresponding to the equivalent transconductance value (K*gm) mentioned above is equal to the value Rx in equation (2), and the transconductance value gmx of the compensation current source  220  corresponds to a parameter gmx in equation (2). Therefore, if in equation (1), the value of the parameters Ro or the parameter L of the corresponding stand-alone component varies, the control circuit  310  may adjust the control current I 1  according to the variations of the voltage difference (Vop−Von) of the output terminals Vop and Von of the receiver  110 , in order to adjust the equivalent transconductance value (K*gm) of the current sources  351 - 1 ,  351 - 2 , . . . , and  351 -K (i.e., to adjust the value Rx mentioned above) and adjust the transconductance value gmx of the compensation current source  220 , so as to satisfy the conditions described by equations (1) and (2). As a result, the baseline wandering phenomenon can be effectively corrected. In addition, in this embodiment, even if the conditions described by equations (1) and (2) are not completely satisfied, the baseline wandering phenomenon and side effects thereof can be reduced by a significant degree. As a result, the side effects such as data inaccuracy can be prevented. 
   Please refer to  FIG. 5 .  FIG. 5  is a schematic view of a receiving device according to a variant embodiment shown in  FIG. 1 , where the baseline wandering correction device  202  comprises a compensation current source  21  and a voltage signal generator  230  comprising a control circuit  232  and a voltage generation unit  234 . The control circuit  232  outputs a control signal Ctrl 2  to the voltage generation unit  234  according to the reference voltage Voffset and the voltages of output terminals Vop and Von, in order to adjust parameter(s) of at least one component in the voltage generation unit  234 . The voltage generation unit  234  outputs the control voltage Vx to the compensation current source  21  according to the control signal Ctrl 2 , the voltages of the output terminals Vop and Von, and the reference voltage Vth. The compensation current source  21  outputs the compensation current Ix to the receiver  110  according to the control voltage Vx to correct the baseline wandering phenomenon. 
   Please refer to  FIG. 6  and  FIG. 7 .  FIG. 6  is a diagram of a voltage signal generator according to another embodiment of the present invention, where the architecture shown in  FIG. 6  can be applied to the embodiment shown in  FIG. 5 , and  FIG. 7  is a diagram of the impedance  35   b  shown in  FIG. 6 . The control circuit  330  and the voltage generation unit  340  shown in  FIG. 6  respectively correspond to the control circuit  232  and the voltage generation unit  234  shown in  FIG. 1 , where the control circuit  330  comprises the two comparators  312  and  314  as mentioned above and a counter  336 . The operations of the two comparators  312  and  314  have been disclosed in the embodiment shown in  FIG. 2 . The counter  336  is well known in the art, and therefore is not explained in detail herein. Different architecture of the control circuit and the voltage generation unit can be applied to other embodiments of the present invention. 
   As shown in  FIG. 6  and  FIG. 7 , the counter  336  receives the comparison results respectively outputted by the comparators  312  and  314  through an increase control terminal N_up and a decrease control terminal N_down thereof, and outputs the control signal Ctrl 2  (which carries a count value in this embodiment) to the impedance  35   b  according to at least one of the comparison results. The impedance  35   b  comprises the capacitor  352  and a variable resistor (the portion with the equivalent resistance value Rx shown in  FIG. 7 ), which are arranged in parallel. In this embodiment, the variable resistor comprises L switching circuits, where each switching circuit comprises a switch  353 -J and a resistor  354 -J connected in series (J=1, 2, . . . , L). In addition, the control circuit  330  controls the number of switches to be turned on within the switches  353 - 1 ,  353 - 2 , . . . , and  353 -L by determining the count value that the control signal Ctrl 2  carries, in order to control the equivalent resistance value Rx. It is noted that the control circuit  330  merely adjusts the equivalent resistance value Rx without adjusting the transconductance value gmx of the compensation current source  21 . In this embodiment, even though the conditions described by equations (1) and (2) are not always completely satisfied, the baseline wandering and the side effects thereof can still be reduced by a significant degree. As a result, the side effects such as the data inaccuracy can be prevented. 
   In a variation of the embodiment shown in  FIG. 5 , in order to roughly approach or completely satisfy the conditions described by equations (1) and (2), a digital-to-analog converter can be utilized for converting the count value carried by the control signal Ctrl 2  and outputting the converted count value to the compensation current source  21  to adjust the transconductance value gmx of the compensation current source  21 , where the product of the transconductance value gmx of the compensation current source  21  and the equivalent resistance value Rx can as a result be maintained a constant. 
   Please refer to  FIG. 8  and  FIG. 9 .  FIG. 8  is a diagram of a voltage signal generator according to yet another embodiment of the present invention, where  FIG. 9  is a diagram of the impedance  35   c  shown in  FIG. 8 . The control circuit  350  and the voltage generation unit  360  shown in  FIG. 8  are similar to those shown in  FIG. 6 . However, in the control circuit  350  shown in  FIG. 8 , the comparators  312  and  314  are respectively coupled to the decrease control terminal N_down and the increase control terminal N_up of the counter  336 . In addition, the impedance  35   c  comprises a resistor  351  and a variable capacitor (the portion with the equivalent capacitance value C shown in  FIG. 9 ), which are arranged in parallel. In this embodiment, the variable capacitor comprises M switching circuits, where each switching circuit comprises a switch  355 -J and a capacitor  356 -J connected in series (J=1, 2, . . . , M). The control circuit  350  controls the number of switches to be turned on within the switches  355 - 1 ,  355 - 2 , . . . , and  355 -M by determining the count value that the control signal Ctrl 2  carries, in order to control the equivalent capacitance value C. As a result, when the parameter Ro or the parameter L in equation (1) varies, the conditions described by equations (1) can be roughly approached or completely satisfied. 
   Please refer to  FIG. 10 .  FIG. 10  is a diagram of a voltage signal generator according to yet another embodiment of the present invention, where the difference between the embodiments respectively shown in  FIG. 2  and  FIG. 10  is described as follows. The control circuit  310  of the embodiment shown in  FIG. 10  adjusts the current value Ic of current sources  381  and  382  and the current value  21   c  of current sources  383  and  384  to roughly approach or completely satisfy the conditions described by equations (1) and (2), where the current adjustment of the current sources  381 ,  382 ,  383 , and  384  can be implemented utilizing current mirror architecture. 
   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.