Adaptation of baseline wander correction loop gain settings

Abstract

An apparatus includes a first circuit and a second circuit. The first circuit may be configured to receive a signal, where low frequency content of the signal is attenuated due to high pass filtering by a medium carrying the signal and a coupling. The second circuit may be configured to automatically set a gain of a baseline wander correction loop to restore the low frequency content in the signal based upon a sample taken from a first point in a signal pathway of the first circuit.

1 . An apparatus comprising:
 a first circuit configured to receive a signal having low frequency content attenuated due to high pass filtering by a medium carrying said signal and a coupling, wherein said first circuit comprises an error signal generator configured to generate an error signal in response to a sample taken at an input of a detector in a signal pathway of said first circuit and a sample taken at an output of said detector; and   a second circuit configured to automatically set a gain of a baseline wander correction loop to restore said low frequency content in said signal based upon a sample taken from a first point in said signal pathway of said first circuit, wherein said second circuit comprises a gain adaptation circuit configured to set said gain of said baseline wander correction loop in response to a baseline wander correction signal and said error signal.   
     
     
         2 . The apparatus according to  claim 1 , wherein said second circuit further comprises a low pass filter configured to generate said baseline wander correction signal in response to said sample taken from said first point in said signal pathway of said first circuit. 
     
     
         3 . The apparatus according to  claim 2 , wherein said low pass filter comprises at least one of an analog low pass filter and a digital low pass filter. 
     
     
         4 . The apparatus according to  claim 2 , wherein said second circuit further comprises a second low pass filter configured to generate a second baseline wander correction signal in response to said sample taken from said first point in said signal pathway of said first circuit. 
     
     
         5 . The apparatus according to  claim 4 , wherein said low frequency content in said signal is restored by adding a feedback signal to a second point in the signal pathway of said first circuit and said second circuit further comprises a multiplier configured to generate said feedback signal by scaling said second baseline wander correction signal based upon said gain. 
     
     
         6 . The apparatus according to  claim 2 , wherein:
 said low pass filter comprises an analog low pass filter;   said baseline wander correction signal generated by said analog low pass filter is presented to either a latch or an analog-to-digital converter; and   said gain of said baseline wander correction loop is adapted based upon an output of said latch or said analog-to-digital converter and said error signal.   
     
     
         7 . The apparatus according to  claim 2 , wherein said second circuit further comprises a data processing circuit configured to control said low pass filter based upon said sample taken from said first point in said signal pathway of said first circuit. 
     
     
         8 . The apparatus according to  claim 1 , wherein said coupling comprises at least one of an AC coupling capacitor and a transformer. 
     
     
         9 . The apparatus according to  claim 1 , wherein said first circuit comprises a receiver circuit, said signal pathway comprises a receiver chain of said receiver circuit, and said second circuit comprises a baseline wander correction circuit. 
     
     
         10 . The apparatus according to  claim 1 , wherein the first point in the signal pathway of said first circuit from which said sample is taken comprises one of said output of said detector, said input of said detector, an output of a slicer, an input of said slicer, an output of an equalizer, an input of said equalizer, and an input of a summing node of said receiver. 
     
     
         11 . The apparatus according to  claim 10 , wherein said equalizer comprises at least one of a linear equalizer and a decision feedback equalizer. 
     
     
         12 . The apparatus according to  claim 1 , wherein said low frequency content in said signal is restored by adding a feedback signal generated by said second circuit to a second point in the signal pathway of said first circuit. 
     
     
         13 . The apparatus according to  claim 1 , wherein said apparatus is fabricated in an integrated circuit. 
     
     
         14 . A method of correcting baseline wander comprising:
 receiving a signal, wherein low frequency content of said signal is attenuated due to high pass filtering by a medium carrying said signal and a coupling method for communicating said signal to a receiver; and   automatically setting a gain of a baseline wander correction loop to restore said low frequency content in said signal based upon a sample taken from a first point in a signal pathway of said receiver after the coupling, wherein automatically setting said gain comprises (i) generating a baseline wander correction signal in response to said sample taken from said first point in said signal pathway of said receiver using a low pass filter, (ii) setting said gain of said baseline wander correction loop in response to said baseline wander correction signal and an error signal using a gain adaptation loop and (iii) generating said error signal in response to a sample taken at an input of a detector in said signal pathway of said receiver and a sample taken at an output of said detector using an error signal generator.   
     
     
         15 . The method according to  claim 14 , wherein correcting said baseline wander comprises low pass filtering said signal taken from said first point in said signal pathway. 
     
     
         16 . The method according to  claim 14 , further comprising:
 generating a product of a gain value and an output of a low pass filter configured to filter said signal taken from said first point in said signal pathway; and   adding said product to said signal at a second point in said signal pathway after said coupling.   
     
     
         17 . The method according to  claim 16 , wherein the gain value is set based upon a detector error signal and a digital representation of said baseline wander correction signal. 
     
     
         18 . The method according to  claim 14 , wherein said gain for said baseline wander correction loop is automatically adapted based on channel loss and changes in transmitter de-emphasis setting.