Abstract:
An analog and digital auto-gain control method includes the steps of: providing a gain-mapping table; determining an analog gain level according to a power of a far-end transmitted signal; obtaining a gain-mapping value from the gain-mapping table according to the analog gain level; obtaining a digital gain value according to the gain-mapping value; and adjusting a gain of a digital signal according to the digital gain value. A receiver that performs the auto-gain control method is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwanese application no. 096148654, filed on Dec. 19, 2007, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a communications system, more particularly to a receiver of a communications system and to an auto-gain control method of the receiver. 
     2. Description of the Related Art 
     The development of communications systems with high bit transmission rates is inevitable to cope with the explosion of digital information. Although there currently exists a 10 Gbase-Fiber (IEEE 802.3ae) standard, the use of fiber optics as a transmission medium does not meet requirements for low cost transmission. Therefore, a 10Gbase-T (IEEE 802.3an) standard was proposed, which uses a twisted-pair copper wire as a transmission medium in order to promote and make popular the establishment of ultra-high speed Ethernet systems. 
     Referring to  FIG. 1 , in a conventional network transmission environment, each transceiver pair  1  comprises a receiver  2  and a transmitter  3 . In general, the receiver  2  comprises components, such as an analog front end (AFE) unit, an analog-to-digital converter (ADC), a crosstalk suppressing unit, an equalizer, etc. The analog front end unit comprises an analog auto gain controller (AAGC). When establishing a connection, the receiver  2  will first determine signal power of the transmitter  3  before determining an optimum analog gain level of the analog auto gain controller. 
     In general, it is only after the analog gain level has been determined that the receiver  2  converges coefficients of the crosstalk suppressing unit, a feed forward equalizer and a feedback equalizer. Therefore, when the signal power of a far end or near end transmitter  3  changes, the analog gain level of the analog auto gain controller of the receiver  2  changes accordingly, such that the coefficients of the crosstalk suppressing unit, the feed forward equalizer and the feedback equalizer must be converged anew. Taking a 10 Gbase-T Ethernet network that complies with the IEEE 802.3an standard as an example, frequent adjustment of the signal power of the transmitter  3  is necessary when establishing a connection so as to avoid excessive signal power that can result in crosstalk with other receivers  2 . Re-converging of coefficients can easily lead to disconnection and re-connection problems. 
     Therefore, in order to make the process of establishing a connection smoother, there is a need to dispense with re-converging of the coefficients of the receiver  2  whenever the signal power of the transmitter  3  is adjusted during connection establishment. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a receiver and a method for gain control that can overcome the aforesaid drawbacks of the conventional communications system. 
     According to one aspect of the present invention, there is provided a method for gain control that comprises the steps of: providing a gain-mapping table; determining a first analog gain level according to power of a far-end transmitted signal; obtaining a first gain-mapping value from the gain-mapping table according to the first analog gain level; obtaining a first digital gain value according to the first gain-mapping value; and adjusting a gain of a digital signal according to the first digital gain value. 
     According to another aspect of the present invention, there is provided a receiver that comprises: an analog front end (AFE) including an analog auto gain controller (AAGC), the receiver determining a first analog gain level of the AAGC according to power of a transmitted signal transmitted by a far-end device; an analog-to-digital converter (ADC) for converting an output of the AFE into a digital signal; a first digital auto gain controller (DAGC), disposed in a data processing path, for adjusting a gain of the digital signal; and a gain processing unit including a gain-mapping table, the gain processing unit obtaining a first gain-mapping value from the gain-mapping table according to the first analog gain level, and obtaining a first digital gain value of the first DAGC according to the first gain-mapping value. 
     According to yet another aspect of the present invention, there is provided a receiver. The receiver comprises: an analog front end (AFE) for processing an analog signal received by the receiver, the AFE including an analog auto gain controller (AAGC) for adjusting an analog gain of the analog signal according to an analog gain value; an analog-to-digital converter (ADC) for converting a processed analog signal from the AFE into a digital signal; a data processing module for processing the digital signal from the ADC, the data processing module including a first digital auto gain controller (DAGC) for adjusting a gain of the digital signal according to a first digital gain value; and a gain processing unit coupled to the first DAGC for determining the first digital gain value according to the analog gain value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic diagram of a conventional 10Gbase-T network transmission framework; 
         FIG. 2  is a system block diagram of the first preferred embodiment of a receiver according to the present invention; 
         FIG. 3  is a flowchart of the first preferred embodiment of an analog and digital auto gain control method according to the present invention; 
         FIG. 4  is a system block diagram of the second preferred embodiment of a receiver according to the present invention; 
         FIG. 5  is a system block diagram of the third preferred embodiment of a receiver according to the present invention; 
         FIG. 6  is a system block diagram of the fourth preferred embodiment of a receiver according to the present invention; 
         FIG. 7  is a flowchart of the fourth preferred embodiment of an analog and digital auto gain control method according to the present invention; 
         FIG. 8  is a system block diagram of the fifth preferred embodiment of a receiver according to the present invention; and 
         FIG. 9  is a system block diagram of the sixth preferred embodiment of a receiver according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the present invention is described in greater detail with reference to the accompanying preferred embodiments, it should be noted herein that like elements are denoted by the same reference numerals throughout the disclosure. 
     Referring to  FIGS. 2 and 3 , the first preferred embodiment of a receiver  4  according to the present invention is shown to include an analog front end (AFE)  41 , an analog-to-digital converter (ADC)  42 , a first digital auto gain controller (DAGC)  43 , a gain processing unit  44 , an interference canceller  45 , a second digital auto gain controller (DAGC)  46 , a feed forward equalizer (FFE)  47 , a feedback equalizer (FBE)  48 , and a slicer  49 . The first DAGC  43 , the FFE  47 , the FBE  48  and the slicer  49  are disposed in a primary data processing path, whereas the interference canceller  45  and the second DAGC  46  are disposed in an interference cancellation path. The AFE  41  comprises an analog auto gain controller (AAGC)  411 . The gain processing unit  44  comprises a gain-mapping table  441 . 
     At the start, the AFE  41  receives an analog signal, and the AAGC  411  performs analog gain adjustment of the analog signal according to an analog gain value. The ADC  42  converts the analog signal processed by the AFE  41  into a digital signal, which is processed by the first DAGC  43 . The output of the interference canceller  45  is processed by the second DAGC  46 , and the outputs of the first and second DAGC  43 ,  46  are combined for subsequent processing in the primary data processing path. The first and second DAGC  43 ,  46  are controlled by the gain processing unit  44 . 
     In the receiver  4 , the interference canceller  45  disposed in the interference cancellation path is used to remove (cancel) noise, such as an echo, a near end crosstalk (NEXT), a far end crosstalk (FEXT), etc., whereas the FFE  47 , the FBE  48  and the slicer  49  disposed in the primary data processing path are used to process a far end transmitted signal received by the receiver  4 . Since the functions and operations of these components can be readily appreciated by those skilled in the art, further details of the same are omitted herein for the sake of brevity. 
     The first preferred embodiment of the analog and digital auto gain control (AGC) method of the present invention comprises the following steps. 
     In step  51 , before establishing a network connection, the gain processing unit  44  provides a gain-mapping table  441 . It is noted that the gain range of the AAGC  411  can vary among different receivers  4  due to factors, such as manufacturing drift, temperature, operational voltage, degradation of components, etc. Therefore, the gain-mapping table  441  is set before a network connection is established. 
     To set the gain-mapping table  441 , a transmitter (not shown) of a transceiver is used to transmit a test signal, which is received by a receiver  4  of the transceiver. The AAGC  411  is set at a specified analog gain value (or analog gain level) at this time, and output power (recorded as a gain-mapping value) is measured at the output end of the ADC  42 . By repeating the above steps for different analog gain levels, power differences among the analog gain levels of the AAGC  411  can be obtained for setting the gain-mapping table  441  (see Table 1). 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Level of the analog auto gain controller 
                 Gain-mapping value 
               
               
                   
                   
               
             
             
               
                   
                 analog gain level 1 
                 Gain-mapping value 1 
               
               
                   
                 analog gain level 2 
                 Gain-mapping value 2 
               
               
                   
                 . . . 
                 . . . 
               
               
                   
                 analog gain level N 
                 Gain-mapping value N 
               
               
                   
                   
               
             
          
         
       
     
     In step  52 , during the process of establishing a network connection, the receiver  4  will first determine the power of a transmitted signal to be transmitted to a far-end device, and the power of a far-end transmitted signal transmitted by a transmitter of the far-end device. The power of a near-end interference signal can be determined from the power of the transmitted signal to be transmitted to the far-end device. Then, the receiver  4  determines a first analog gain level of the AAGC  411  according to the power of the far-end transmitted signal, and a second analog gain level of the AAGC  411  according to the power of the near-end interference signal. 
     In steps  53  to  55 , the gain processing unit  44  obtains a first gain-mapping value from the gain-mapping table  441  according to the first analog gain level, and then calculates a first digital gain value. In an embodiment, the first digital gain value is an inverse of the first gain-mapping value. The first digital gain value is used to set the first DAGC  43 . In a similar manner, the gain processing unit  44  obtains a second gain-mapping value from the gain-mapping table  441  according to the second analog gain level, and then generates a second digital gain value. In an embodiment, the second digital gain value is an inverse of the second gain-mapping value. The second digital gain value is used to set the second DAGC  46 . 
     In step  56 , the coefficients of the interference canceller  45 , the FFE  47  and the FBE  48  can be converged after the step  55 , and need not undergo re-converging. 
     Referring to  FIG. 4 , the second preferred embodiment of a receiver  4  according to this invention comprises the AFE  41 , the ADC  42 , the first DAGC  43 , the gain processing unit  44 , the interference canceller  45 , the second DAGC  46 , the FFE  47 , the FBE  48  and the slicer  49  shown in  FIG. 2 . The functions of these components are similar to those in the first preferred embodiment. The second preferred embodiment differs from the first preferred embodiment in that: The digital signal from the ADC  42  is first processed by the FFE  47  before undergoing processing by the first DAGC  43 . Like the previous embodiment, the output of the interference canceller  45  is processed by the second DAGC  46 , and the outputs of the first and second DAGC  43 ,  46  are combined for subsequent processing in the primary data processing path. The first DAGC  43  and the second DAGC  46  are set by the gain processing unit  44  in a manner similar to that in the first preferred embodiment. 
     Referring to  FIG. 5 , the third preferred embodiment of a receiver  4  according to this invention is disclosed. The functions of the components of the third preferred embodiment are similar to those of the first preferred embodiment. The third preferred embodiment differs from the first preferred embodiment in that: The output of the first DAGC  43  is first processed by the FFE  47 , and the outputs of the FFE  47  and the second DAGC  46 , which is responsible for processing the output of the interference canceller  45 , are combined for subsequent processing in the primary data processing path. The first DAGC  43  and the second DAGC  46  are set by the gain processing unit  44  in a manner similar to that in the first preferred embodiment. 
       FIGS. 6 and 7  show the fourth preferred embodiment of a receiver  4  according to this invention. The functions of the components of the fourth preferred embodiment are similar to those of the first preferred embodiment. The fourth preferred embodiment differs from the first preferred embodiment in that: The output of the second DAGC  46 , which is responsible for processing the output of the interference canceller  45 , is combined with the digital signal from the ADC  42  to result in a combined signal. The combined signal is processed by the first DAGC  43  before undergoing further processing in the primary data processing path. Moreover, the gain processing unit  44  generates the second digital gain value in a different manner. 
     The fourth preferred embodiment of the analog and digital AGC method of the present invention comprises steps similar to those in the first preferred embodiment. The method of the fourth preferred embodiment differs from the first preferred embodiment in the calculation of the second digital gain value. As shown in step  57  in  FIG. 7 , the second digital gain value is generated according to the first and second gain-mapping values. In this embodiment, the second digital gain value is a product of the first gain-mapping value and an inverse of the second gain-mapping value. 
       FIG. 8  shows the fifth preferred embodiment of a receiver  4  according to this invention. The functions of the components of the fifth preferred embodiment are similar to those of the fourth preferred embodiment. The fifth preferred embodiment differs from the fourth preferred embodiment in that: The digital signal from the ADC  42  is first processed by the FFE  47 , and the output of the second DAGC  46 , which is responsible for processing the output of the interference canceller  45 , is combined with the output of the FFE  47  to result in a combined signal. The combined signal is then processed by the first DAGC  43  before undergoing further processing in the primary data processing path. The first DAGC  43  and the second DAGC  46  are set by the gain processing unit  44  in a manner similar to that in the fourth preferred embodiment. 
       FIG. 9  shows the sixth preferred embodiment of a receiver  4  according to this invention. The functions of the components of the sixth preferred embodiment are similar to those of the fourth preferred embodiment. The sixth preferred embodiment differs from the fourth preferred embodiment in that: The digital signal from the ADC  42  is first combined with the output of the second DAGC  46 , which is responsible for processing the output of the interference canceller  45 , to generate a combined signal. The combined signal is processed in sequence by the FFE  47  and the first DAGC  43  before undergoing further processing in the primary data processing path. The first DAGC  43  and the second DAGC  46  are set by the gain processing unit  44  in a manner similar to that in the fourth preferred embodiment. 
     In sum, through processing of the first DAGC  43  and the second DAGC  46 , even though the level of the AAGC  411  changes with the signal power, the coefficients of the interference canceller  45 , the FFE  47  and the FBE  48  are converged during initial setting of the AAGC  411  and need not undergo re-converging. For various applications (such as 10Gbase-T) that involve repeated adjustment of signal power of a transmitter and the receiver  4  when establishing a network connection, the process of establishing the network connection is made smoother accordingly. 
     While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.