Data path differentiator for pre-emphasis requirement determination or slot identification

Abstract

An apparatus and method is disclosed for generating path length information for two (usually redundant) receive paths in a receiving device such as a server blade so that the proper amount of equalization and/or pre-emphasis may be applied to receiver and driver circuits in the server blade. In one embodiment, the path length information comprises a longer or shorter path determination, and may also include a estimation of the slot location. In another embodiment, the path length information comprises a representation of the length of two receive paths. The path length information generating circuit is connected to the two receive inputs of the receiving device though high impedance elements, and the path length information may be utilized by hardware or a processor to set the equalization or pre-emphasis in the receiver and/or driver.

1 . A communication device comprising:
 a first filter operably coupled to a first receive path;   a second filter operably coupled to a second receive path; and   a path length determination circuit operably coupled to the first filter and the second filter, the path length determination circuit operable to generate path length information according to the first receive path and the second receive path.   
     
     
         2 - 26 . (canceled) 
     
     
         27 . The communication device as recited in  claim 1 , wherein the path length information comprises an identification of which of the first receive path and the second receive path is longer. 
     
     
         28 . The communication device as recited in  claim 1 , wherein the path length determination circuit comprises at least one envelope detector operable to generate a characteristic of a communication signal on the first receive path and the second receive path. 
     
     
         29 . The communication device as recited in  claim 1 , wherein the path length information comprises a magnitude of a difference between a longer and a shorter of the first receive path and the second receive path. 
     
     
         30 . The communication device as recited in  claim 1 , wherein the path length determination circuit comprises a differential amplifier operably coupled to the first filter and the second filter, the differential amplifier operable to generate a voltage representative of a magnitude of a difference between a longer and a shorter of the first receive path and the second receive path. 
     
     
         31 . The communication device as recited in  claim 1 , wherein the communication device comprises at least one equalization circuit. 
     
     
         32 . The communication device as recited in  claim 31 , wherein the at least one equalization circuit is operable to equalize at least one of the first receive path and the second receive path according to the path length information. 
     
     
         33 . The communication device as recited in  claim 32 , wherein the equalization circuit is operable to adapt the equalization according to a change in the path length information. 
     
     
         34 . The communication device as recited in  claim 1 , wherein the communication device comprises at least one pre-emphasis circuit operable to apply pre-emphasis to at least one transmit path according to the path length information. 
     
     
         35 . The communication device as recited in  claim 34 , wherein the at least one pre-emphasis circuit is operable to adapt the pre-emphasis according to a change in the path length information. 
     
     
         36 . A method for operating a communication device, the method comprising:
 filtering a first receive path to generate a first filtered receive path;   filtering a second receive path to generate a second filtered receive path; and   generating path length information according to the first filtered receive path and the second filtered receive path.   
     
     
         37 . The method for operating a communication device as recited in  claim 36 , wherein the path length information comprises an identification of which of the first receive path and the second receive path is longer. 
     
     
         38 . The method for operating a communication device as recited in  claim 36 , wherein the method comprises generating a characteristic of the first receive path and a characteristic of the second receive path. 
     
     
         39 . The method for operating a communication device as recited in  claim 36 , wherein the path length information comprises a magnitude of a difference between a longer and a shorter of the first receive path and the second receive path. 
     
     
         40 . The method for operating a communication device as recited in  claim 36 , wherein the method comprises generating a voltage representative of a magnitude of a difference between a longer and a shorter of the first receive path and the second receive path. 
     
     
         41 . The method for operating a communication device as recited in  claim 36 , wherein the method comprises equalizing the first receive path according to the path length information. 
     
     
         42 . The method for operating a communication device as recited in  claim 41 , wherein the method comprises equalizing the second receive path according to the path length information. 
     
     
         43 . The method for operating a communication device as recited in  claim 41 , wherein the method comprises adapting the equalization according to a change in the path length information. 
     
     
         44 . The method for operating a communication device as recited in  claim 36 , wherein the method comprises applying pre-emphasis to at least one transmit path according to the path length information. 
     
     
         45 . The method for operating a communication device as recited in  claim 44 , wherein the method comprises adapting the pre-emphasis according to a change in the path length information. 
     
     
         46 . A communication device comprising:
 a first filter operably coupled to a first receive path;   a second filter operably coupled to a second receive path;   a characteristic determination circuit operably coupled to the first filter and second filter, the characteristic determination circuit operable to generate characteristic information according to the first receive path and the second receive path; and   a pre-emphasis circuit operable to apply pre-emphasis to at least one transmit path according to the characteristic information.   
     
     
         47 . The communication device as recited in  claim 46 , wherein the characteristic information comprises an identification of which of the first receive path and the second receive path is longer. 
     
     
         48 . The communication device as recited in  claim 46 , wherein the characteristic determination circuit comprises at least one envelope detector operable to generate a path length of a communication signal on the first receive path and the second receive path. 
     
     
         49 . The communication device as recited in  claim 46 , wherein the characteristic information comprises a magnitude of a difference between a longer and a shorter of the first receive path and the second receive path. 
     
     
         50 . The communication device as recited in  claim 46 , wherein the characteristic determination circuit comprises a differential amplifier operably coupled to the first filter and the second filter, the differential amplifier operable to generate a voltage representative of a magnitude of a difference between a longer and a shorter of the first receive path and the second receive path. 
     
     
         51 . The communication device as recited in  claim 46 , wherein the communication device comprises at least one equalization circuit. 
     
     
         52 . The communication device as recited in  claim 51 , wherein the at least one equalization circuit is operable to equalize at least one of the first receive path and the second receive path according to the characteristic information. 
     
     
         53 . The communication device as recited in  claim 52 , wherein the equalization circuit is operable to adapt the equalization according to a change in the characteristic information. 
     
     
         54 . The communication device as recited in  claim 46 , wherein the pre-emphasis circuit is operable to adapt the pre-emphasis according to a change in the characteristic information.