Adaptation of baseline wander correction loop gain settings
An apparatus including 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, wherein low frequency content of said signal is attenuated due to high pass filtering by a medium carrying said signal and a coupling; 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 a signal pathway of said first circuit, 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,
said second circuit comprises (i) a first low pass filter, (ii) a second low pass filter, (iii) a multiplier, and (iv) a gain adaptation circuit,
said first low pass filter and said second low pass filter are configured to generate a first baseline wander correction signal and a second baseline wander correction signal respectively, in response to said sample taken from said first point in said signal pathway of said first circuit,
said multiplier is configured to generate said feedback signal by scaling said second baseline wander correction signal based upon said gain of said baseline wander correction loop, and
said gain adaptation circuit is configured to set said gain of said baseline wander correction loop in response to said first baseline wander correction signal and an error signal.
2. The apparatus according to claim 1 , wherein said coupling comprises at least one of an AC coupling capacitor and a transformer.
3. 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.
4. The apparatus according to claim wherein the first point in the signal pathway of said first circuit from which said sample is taken comprises one of an output of a detector, an 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.
5. The apparatus according to claim 4 , wherein said equalizer comprises at least one of a linear equalizer and a decision feedback equalizer.
6. The apparatus according to claim 1 , wherein said first low pass filter comprises at least one of an analog low pass filter and a digital low pass filter.
7. The apparatus according to claim 1 , wherein:
said first low pass filter comprises an analog low pass filter;
said first 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.
8. An apparatus comprising:
a first circuit configured to receive 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; 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 a signal pathway of said first circuit, wherein said second circuit comprises a first low pass filter and a second low pass filter configured to generate a first baseline wander correction signal and a second baseline wander correction signal, respectively, and a gain of the first baseline wander correction signal is automatically adapted based upon an error signal and the second baseline wander correction signal.
9. The apparatus according to claim 8 , wherein said second low pass filter is configured to match a transfer function of said first low pass filter.
10. The apparatus according to claim 8 , wherein adaptation of said gain implements at least one of least mean squares and sign-sign least mean squares.
11. The apparatus according to claim 8 , wherein said second low pass filter comprises a digital low pass filter.
12. The apparatus according to claim 1 , 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.
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 first baseline wander correction signal and a second baseline wander correction signal in response to said sample taken from said first point in said signal pathway of said receiver using a first low pass filter and a second low pass filter, respectively, and (ii) setting a gain of said first baseline wander correction signal based upon said second baseline wander correction signal and an error signal using a gain adaptation loop.
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 said first 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 14 , wherein said gain for said first low pass filter is automatically adapted based on channel loss and changes in transmitter de-emphasis setting.
18. The method according to claim 16 , wherein the gain value is set based upon a detector error signal and a digital representation of said first baseline wander correction signal.